THE STOMA.TAL RELATIONSHIPS, LEVELOPl^IENT, AND MATURE STRUCTURE OE SOME AMARYLLIDACEOUS LEAVES.______

An in v e s t ig a t io n has been made o f:

i) Variations in the number and form of the stomata, papillae, and ordinary epidermal cells over the individual leaf. ii) Growth of the leaf with special reference to meristematic activity, and the vascular system. iii) Comparative anatomy of Amaryllidaceous leaves with special reference to the inverted bundle system.

Variations in the water supply to the successive intercalary portions of the leaf cause variations in the degree of expansion of the epidermal cells. This modifies the stomatal freq.uencies (numbers per unit area) as otherwise determined by the index value (proportion of epidermal units converted into stomata). The typical frequency gradients are: i. Increasing gradient from base to­ wards the apex of the leaf, with a secondary decrease at the apex. ii. Increasing gradient from the mid-rib to the margin for broad leaves, and decreasing for narrow leaves. Stomatal indices are more constant than frequencies, but give similar gradients. The basal growth of the leaf-limb is due to: i. Meristematic activity and auxesis of the peripheral tissues forming the epidermis and assimilating tissues. ii. Auxesis only of the central ground-tissue. The extent of mature leaf-limb increases during growth but its water supply is limited by the amount that can be conducted through the extending zone. This supply improves due to the lignification of the immature tracheids present in the dormant l e a f . In only six genera of the Amaryllidaceae are concentric leaves found excluding the Conostylideae. These leaves have adaxial inverted bundles which were found to differ in their mode of connection with the stem system. They may curve round into the sheathing portion of the leaf- base, passing directly to the stem system as in lanthe, or they may be independent, ending in groups of storage tracheids in the upper part of the leaf-base, as in Narcissus roeticus. and Zeohvranthes Candida. It is difficult to harmonise the results from the two latter with the Phyllode theory.

^ THE STOMATAL RELATIONSHIPS, DEVELOPMENT AND MATURE STRUCTURE OF SOME AMARYLLIDACEOUS LEAVES.

by L i l l i a n Mary W icks.

CONTENTS.

General Introduction. Part I. The variations in number and form of the stomata, papillae, and ordinary epidermal eells over the individual leaf as found in the Amaryllidaceae.

Broad Leaves. i. Hae man thus eocoineus,L. ii. Haemanthus rotundifolius, Gawl. iii. Haemanthus albiflos, Jacq. ( a note) iv. Brunsvigia gigantea, Heist. V. Hymenoeallis festalis, ( «Hymenooallis calathina, Nichols, x Elisena longipetala. H erb.)

Narrow Le ave s .

i. Galanthus nivalis, L. ii. Ammo char is falcata, (L^H^rit) Herb. iii. Narcissus poeticus, L .-

Summary.

Description of figures. F ig u r e s .

Part II. The anàtomy of the Dormant Leaf, and of the leaf at various stages of Growth with special reference to meristematic activity and the vascular system. Description for Narcissus poeticus, L. and comparison with N.Elvira ( s N. poeticus,L. var. ornatus, Haw. X N. tazetta, L.) ProQuest Number: 10097160

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Section. 1. Prior to the resting stage. ( N. hulbocodium,L. var. citrinus,BakO 2 . Resting stage. 3 . Half-grown leaf. 4 . Mature leaf. 5 . Comparison of the growth of leaves of Narcissus with those of Galanthus nivalis, L. and Zephyranthes Candida, Herb.. ti 6 . Anatomy and growth of the scale leaf and comparison with that of Haemanthus albiflos, Jacq.

Summary. Description of figures. F ig u r e s .

P a r t. I I I . Comparative anatomy of Amaryllidaceous leaves with special reference to the inverted bundle system.

Section. 1. Anatomy of the bi-facial leaf. 44 2. Extent of the concentric leaf type in the family and its structure. it 3. The origin and significance of the inverted bundle system.

(a) lanthe alba, (linn, fil.) Salisb. lanthe aquatica. (Linn.fil.) W illia m s. (b) Agave americana, L. (c) Narcissus poeticus, L. (d) Zephyranthes Candida, Herb.

Discussion on the Phyllode Theory and the concentric leaf. Summary. Description of Plates and figures.

Plates and figures. Note on Nomenclature. Literature cited. GENERAL INTRODUCT ION.

I. The Interesting results obtained by Salisbury when considering the variations in the stomatal distribution (frequencies) over the Individual leaf suggested the desir­ ability of extending such work to other leaf types. It was also desired to study more fully the interaction of stomatal index (the proportion of epidermal units converted into stomata) and the expansion factor (of the ordinary epidermal cells) in determining the flrequency variations. An attempt has been made to correlate these variations with the variations in water supply during growth. Where papillae are present their mature structure has been described and their distribution considered in the same way as for the stomata, that is, the variation in frequency and index values (the proportion of epidermal units converted into papillae ) have been considered.

II. It has been known for a long time (Steihheil 1837)that many leaves grow for a considerable period due to the activity of a basal zone and that the apex of the leaf-limb is the oldest portion. It was desired to find the extent and period of activity of this meristem and to define the part played by auxesis. If the apex of the leaf is mature and transpiring, the problem arises as to how the water-supply to it is main­ tained through the growing zone, that is, how are the vascular tissues in that zone able to undergo great extension and at the same time conduct an adaquate supply of water to the mature leaf-lim b, which is continously increasing in extent and demand on the water supply. III. The general survey of Amaryllidaceous leaves was under­ taken to find the relationship of the assimilating tissue to the vascular system, and to find how frequent is the occurrence of the concentric type of leaf within the family.

In examining the bases of some leaves with concentric leaf-lim bs inverted bundles were not found in the leaf-base. It soon became obvious that the relationship of this system to the normally orientated one of the stem varied, so a critical in v e s t ig a t io n was made o f a s many d if f e r e n t ty p e s as cou ld be fo u n d . FART I.

THE VARIATIONS IN NUMBER AND FORM OF THE STOMATA, PAPILLAE, AND ORDINARY EPIDERMAL CELLS OVER THE INDIVIDUAL LEAF -

AS FOUND IN THE AIvIARYLLIDACEAE.

A considerable amount of work has been done on the comparison of the structure of the lower and upper leaves of the individual plant. (Zalenski 1904, Yapp 1912, and others). The variations in structure of the leaves belonging to different tiers of a woodland flora have also been invest­ igated in detail (Salisbury 1927). But at present comparat­ ively little detailed work has been done on the variations over the individual leaf. Salisbury (Phil. Trans. Roy. Soc. B. vol. 216,1927 p. 20 - 2 5 ) examined the epidermis of some elongated monocotyledonous leaves and found that the stomatal frequency (the number of stomata per unit area of leaf surface) increases from the base to the apex of the leaf, and from the mid-rib to the margin. He found that these gradients are of ‘‘widespread occurrence,** but are sometimes modified. Thus the leaves of Garex sylvatica show a rapid increase in the frequency values for a short distance from the base of the leaf, followed by a gradual fall towards the apex. Salisbury ( ibid p . 5 0 ) considers the proportion of epidermal units converted into stomata. The numerical relationship he terms the Stomatal Index, for which he gives the formula: I - S/E.t S x 100, where I = the stomatal index, S - the number of stomata per unit area, and E = the number of epidermal cells for the same unit area. Salisbury found that the index values for a given species are more constant than the frequencies which indicates that the variations in the frequency values aie due rather to differences in the degree of expansion of the epidermal cells. Salisbury worked mainly with comparatively small linear leaves. This part of the present investigation is an attempt to extend this work taking other leaf types. For this the large leaves of some Amaryllidaceous species are particularly suitable.

METHOD.

Counts were made of the epidermal constituents, (stomata, papillae if present, and ordinary epidermal cells) at frequent intervals in various parts of the leaf, chiefly along the margins and the median line of the leaf. Gell counts were made with an E. Leitz Wetzlar projection apparatus by means of which the piece of epidermis under observation was re­ flected on a sheet of paper and each cell indicated by mark­ ing the position of its nucleus. At the same time a certain portion of the field was drawn accurately so that the variation in the degree of expansion of the cells could be found. In the first part of the work a large field equal to 2^ sq. mms was usedy while for the narrow leaves considered in the later part a field of I sq. mm was used. The use of a large field minimises the error when considering cells that do not come entirely within the field .

The leaves investigated consist of:- Large broad-leaved forms. Narrow-leaved forms.

All the leaves examined lack sclerenchyma within the tissues and many of them have no definite mid-rib. This is of importance as both factors disturb the normal distribution of the stomata.

B ROAD LEAVES, i HAEMANTHUS COCGINEUS. L.

HaOTanthus coccineus is a mountainous species which produces several erect, Ungulate leaves each year. The elongated bulb is flattened in the upper part, and is composed ’ of the leaf-bases of previous foliage leaves which are distichously arranged, as shown in the two views of the same bulb in Plate I figl. The plant with mature leaves shown in Plate I fig2 was grown in the Bedford Oollege green-house. The leaf examined was cut from this plant and was 14^ inches long and 5 inches broad. The leaf has no definitely marked mid-rib region and is entirely without epidermal papillae.

The frequency values for the margin and median line of both upper and lower surfaces, increase from the base to near the apex of the leaf, where there is a slight fall (fig I). The values for the apical half of the upper surface exhibit a marked fall, followed by a rise to a slightly higher point. This fluctuation within the general gradient is not present in the gradients of the lower surface, and is probably of minor importance as suggested by Salisbury. The margins of the leaf generally have higher frequency values compared with the corresponding points along the median line, especially in the lower half of the leaf (fig 3)* The stomatal frequency variations give a zoned formation when lines are drawn through points with the same values (figs 5 & 6). The steep bends result from the higher values at the margin and the fluctuations for the upper surface are shown by a change in the form of the l i n e s .

The stomatal index gradients are of the same general form as those of the frequencies (fig 2), and the greater uni­ formity of these values is well shown in figs 7 and 8, where the lines of equal values are further apart and more evenly spaced than those of the frequencies.

The influence of another factor is shown by the failure of the frequency curves to correspond exactly with those of the indices (compare figs I & 2). The factor causing the differ­ ences in the two sets of curves is the variation in the degree of expansion of the epidermal cells. Thus at the base of the leaf the epidermal cells are very large, being elongated parallel to the long axis of the leaf as shown in fig 15. Passing towards the apex of the leaf the cells become progress­ ively smaller, when considering either the upper or lower sur­ faces. This is illustrated by figs 15 to 9 for the upper surface. At the apex numerous very small cells occur among the larger ones.

The expansion gradient is thus similar to that of the indices, and the decrease in size of the epidermal cells towards the apex of the leaf results in the closer approximation of the stomata to each other, and so in an increase in the frequency, compared with that determined by the index value.

It is obvious that during development the stomatal frequency gradients are determined firstly by the variations in the index values, and secondly by the degree of expansion of the epidermal cells. In the same way the differences in frequency values for corresponding points on the upper and lower surfaces are due to a lower index value for the lower surface compared with the upper, and to the greater expansion of the epidermal cells of the lower surfaced compared with the upper as is seen by comparing figs 17 and 16. For Haemanthus coccineus the index and expansion factors play about equal parts in determining the frequency values. The variations in the degree of expansion of the epidermal cells is a direct outcome of the variations in the amount of water supplied to the young extending portions of the leaf, mainly the region of auxesis, during growth.

The leaf-base and the apex of the leaf-limb are the first formed parts of the leaf. Increase in the length of the leaf- limb is due to the activity of the tissues at the base of the leaf-limb (see section II). The leaf-base remains within the bulb and acts as a storage organ and so is only of indirect importance in the present consideration. When the tissues of the apex of the young leaf are maturing, the auxesis period, the final extent of the cells depends on the water supply at that period. The apex is dependent upon the amount of lignified xylem in the vascular bundles passing through the the meristematic zone at the base, for its water supply. At this stage only the protoxylem is lignified, and capable of water- conduction, the metaxylem consisting of immature tracheids with considerable cell contents. Thus it is obvious that the amount of water passing to the leaf apex must be small, result­ ing in the production of comparatively small mature cells. During the growing period the metaxylem, passing through the base of the leaf-limb gradually becomes lignifed, and the vascular tissue also increases in amount in the individual bundles. Thus the successive intercalary pieces added to the leaf-lim b, each have a better water supply than the previous ones, which results in a greater expansion of the epidermal cells. Thus the last formed portions at the base of the leaf- limb were formed when the water supply was good, and the epidermal cells are greatly extended longitudinally. This combined with the low stomatal index value, results in a very low frequency value.

In considering the correlation of water relations and frequency distribution over the individual leaf Salisbury (1927 p . 2 4 ) states that the low rate of j water intake by portions of the leaf, remote from the watei^Tavours"high stomatal frequencies As already explained two important factors have to be considered here. F irstly,: whether the region under consideration is mature or not, and secondly, the nature of the conducting tissues. In considering a mature portion of the leaf, it is important to know the nature of the water supply when the tissues were expanding. Thus although the immature apex of the leaf is comparatively near the water supply, the expansion factor is at a minimum owing to the small number of actively conducting elements. 8

Structure of the Stoma.

' The large stomata are sunk below the level of the epidermal cells (figs 18 & 19;. The guard cells are provided with crescent shaped ridges, which partly close the pore above, to the exterior, forming the front cavity, and below to the sub- stomal cavity, forming the back cavity. In the transverse section these ridges appear as horn-like projections with approaching tips which gives the pore an hourglass form. (Wassermann 1924)- A continuation of the cuticle of the leaf surface lines the front and back cavities and the pore-passage as well as the cells bordering the substomal cavity. The large outer horn-like projections (Vbrderhttrnchen) are composed main­ ly of cuticle, having only a small core of cellulose. The inner horn-like projections (HinterHfirnchen) are smaller and strdngly curved, and they are also largely composed of cuticle. To allow for the movements of the stoma the walls of the neighbouring epidermal cells have thin areas where they meet the guard-cells. These areas are termed "hinges" by Haberlandt 1 9 1 4 p .4 4 8. The stomata of the two surfaces are sim ilarly constructed, but those of the lower surface have guard-cells with outer horn-like projections which do not approach so close­ ly at the tips (fig 19).

i i . HAEMANTHUS ROTUNDIFOLIUS, GA^/VL. Haemanthus rotundifolius is a member of the Stellenbosch Flats flora, and contrasts both in habitat and habit with the mountainous species H. coccineus. The bulbs of both species are foliaceous, but those of H. rotundifolius differ in shape, being shorter and distinctly wider in the upper part where flattening takes place. This/sseen by comparing Plate I figs 1 & 3 . A bulb of H. rotundifolius produces only two leaves each year, the leaves being large, suborbicular, and lying closely adpressed to the ground as shown in Plate I fig4 . The leaf examined was a mature one from a young bulb and was 4*4/5 inches wide and 3*1/2 inches long. A larger leaf, with a greater portion of the base present, w ill be examined later as new material has just been obtained.

The epidermis of the upper surface is rough owing to the presence of cells drawn out into papillae. The smoothness of the lower surface is due to the absence of papillae. The papilla frequency (number of papillae per unit area) is highest at the base of the leaf just where it turns into the bulb. These values decrease in all directions to the leaf margin where the lowest values are found (fig 20). It is possible to apply the index formula as in the case of the stomata. It is then found that the papilla index values (the number of epidermal units converted into papillae) show similar gradients to those of the papilla frequencies. structure of the Papilla. The papillae are conical with corrugated sides (fig 22). The apices are complicated, being thrown up into several bulges (fig2 5 ) * The projecting portion of the papilla may be short and broad (fig 2 3 ), or elongated and narrow (fig 24). The thick wall of this part of the papilla consists of a comparatively thin outer cuticularised portion, and a thick inner cellulose portion. The narrowed base of the papilla, which is imbedded in the epidermis between the individual cells, consists of a somewhat thinner cellulose^ which is deeply pitted. ( f i g 2 4 ) The apex of the papilla is mucilaginous and numerous foreign particles are frequently found adhering to it. The mucilage appears to be derived from the chemical alteration of the cut icular portion of the papilla wall. Papillae, mounted in water, and viewed from above have the mucilaginous apical cap preforated with several large holes, (figs 27 and 28) In some cases a single large opening is present as is shown in f i g 2 6 . The papilla contains a well developed protoplast with a large nucleus. The function of the papillae is discussed in the account of sim ilar structures found on the leaves of Brunsvigia gigantea, page 12.

The distribution of stomata.

The stomatal frequencies for the upper surface decrease from the base of the leaf (where it turns into the bulb) out­ wards in all directions so that the lowest values occur around the margin (fig 29). Thus this gradient is similar to that of the papilla frequencies. It is however probable that the values of both decrease rapidly in that part of the leaf-base imbedded in the bulb. The frequency values for the lower surface increase from the base of the leaf outwards towards the margin (fig3 0 ), that is in the opposite direction to the gradient for the upper surface and in the same direction as the gradients of Haemanthus coccineus. The index values are much more constant than those of the frequencies, but definite gradients are present similar to those of the frequencies as shown in figs 31 and 32. The stomatal frequencies for the upper surface range from 65 to 40, and for the lower from 5 to 20 which gives an average difference of 40. For the indices the corresponding figures are3 0 to 25 for the upper surface, and 10 to 25 for the lower, which gives an average difference of 10. It is thus obvious that another factor is at work, and the importance of the expansion factor is evident when corresponding pieces of epidermis are compared from the upper and lower surfaces as in figs 33 to 3 8 ). The cells of the lower surface are frequently seven times as long as those of the upper. This results in very wide spacing of the stomata on the lower surface, and combined with the low index 10 value gives a very low frequency value. The frequency gradient of the upper surface is due almost entirely to the variations in the index values, there being very little difference in the size of the epidermal cells at the base ( f i g 3 8 ) and at the apex (fig 3 4 ) of the upper surface. The epidermal cells of the lower surface from the base of the leaf ( f i g 3 7 ) are considerably larger than those of the apex (fig 33). Thus here the Index and expansion factors combine to form the frequency gradient. Structure of the Stoma.

The stomata have a similar structure to those of Haemanthus coccineus.

Structure of the Epidermis.

The epidermal cells have deeply pitted vertical walls. The very large cells of the lower surface occasionally have two well formed nuclei in each cell. These nuclei are probably formed by the division of the original single nucleus. The small cells of the upper surface never have more than one n u c le u s .

Owing to the sim ilar positions occupied by the papillae and the stomata (figs 3 4 36 3 8 ) it might be possible to con­ sider the papillae as modified stomata or stomatal in itials. In this Investigation the stomatal index values have been found to be more constant than those of the frequencies when com­ paring different parts of the same surface and the lower and upper surfaces. If the papillae are considered as modified stomata then the true stomatal index values for the upper sur­ face are nearly twice as high as those of the lower (Table I). But when considering the papillae as modified epidermal cells the stomatal index values for the upper surface are only slightly higher than those of the lower. For this reason it is believed that the papillae are modified epidermal cells.

T A B L E I. Upper S u rface

Papillae and stomata Papillae calcu­ Index , together taken to re- lated as ordinary values of p rse n t S in the index epidermal cells in 1 th e Lower fo rm u la . the index formula. S u r fa c e .

Apex 3 7 .9 2 1 . 3 2 0 .8

M iddle 4 2 . 1 2 6 .2 2 4 . 0

B ase 4 5 .0 2 2 .6 1 8 .9 11 I

111 HAHIMANTHUS ALBIFLOS, JZCQ. (a note)

The stomatal variations of a leaf from a young bulb of Haemanthus alb iflos, which was obtained from Kew Gardens, were examined. The leaf was Ungulate, 5 inches long, and covered with numerous long silky hairs. Unlike the two species already described the stomatal frequency values are much higher for the lower surface than for the upper. Taking two unit areas for upper and lower surfaces the frequency values are 4 & 1 4 0 respectively (unit area not 1 sq.mm.) The upper surface not only has very few stomata, but a large portion of the apex, a narrow strip along each margin, and the extreme base of the leaf are entirely without stomata as shown in fig 39. In that part of the upper surface having stomata present there is a rise from the base to the middle of the leaf and then a fa ll to the apex in frequency values. The lower surface has no considerable areas without stomata. The frequency values increase rapidly from the base of the leaf to the apex (fig 40). Pigs 41 and 42 show the differences in structure of the upper (A) and the lower (B) surfaces at corresponding points. It is at once seen that the frequency variations are due to differences in the degree of expansion of the epidermal cells as well as to those of index value. Thus stomatal frequency gradients are also a feature of small leaves from young bulbs. i v . BRUNSVIGIA GIGANTEA, HEIST.

Brunsvigia gigantea is a member of the Stellenbosch. Flats flora. The bulb is tunicated in contrast to the foliace­ ous bulbs of Haemanthus coccineus and H. rotundifolius. A large bulb produces six lingulate leaves, which lie adpressed to the ground when mature (Plate II. figs 1 & 2). Thus the habit of this species is similar to that of Haemanthus rotundifolius. The edges of the leaves are ciliated, the cilia being red on the young leaves and brown on the older ones.

A plant grown in Bedford College green-house was found to exhibit considerable movements of its leaves during the growing period. The young leaves do not all move at the same rate, some of them performing a rise to the vertical and a fall to the horizontal once in every two days, and others once in every 48 hours. Thus it frequently happens that some of the leaves are rising while others are falling, or some of the leaves are vertical while others are horizontal. Finally at the end of the growing period movement slows up and finally ceases, all the leaves lying flat on the ground. The leaf examined was cut from a potted plant growing in Bedford College green-house and was 12 inches long, having a maximum width of 4-1/2 inches. 1 2 .

The epidermis. The mature epidermis of the upper surface is composed of ordinary epidermal cells, epidermal cells drawn out into papillae, and stomata. Papillae are absent on the lower sur­ face of the leaf as is seen by comparing figs 52 and 53. The papilla frequency values (number of papillae per unit area) are fairly uniform over the surface of the leaf. The values decrease slightly from the base to the apex of the leaf along the median line (fig 43) and there is a distinct increase from the latter towards the margin. The variations in papilla index values (fig 44) are similar to those of the frequencies ( f i g 4 3 ).

Structure of the Papilla. The papillae occur either singly or in groups of two, three, or four. They occupy a position similar to that of the stomata, that is between the elongated epidermal cells (see fig 56). The papillae of a group may have their pro­ jecting portions quite free or be fused for some distance, which in extreme cases results in double (fig 45) or treble-tipped papilla. All stages can be found from groups of papillae with only the bases of the projecting portions fused, to single papillae with complicated apices. It is possible that the complicated papillae of Haemanthus rontundifolius arose in this way.

The projecting portion of the papilla tends to be cylindrical with a rounded apex (fig 47). The apical portion of the papilla consists of a mucilaginous cap (c) fig 46 with an internal bulge (b). The wall of the projecting portion of the papilla is thick, a comparatively small outer portion of which is cuticlarised. The base of the papilla, which is im­ bedded in the epidermis is thin-walled. In longitudinal section it can be seen that the inner cellulose portion of the wall f orms a chamber at the apex of the papilla by a circular outgrowth (a) within which is found the mucilage plug (b).. This upper chamber is cut off from the lumen of the papilla by a thick cellulose wall (d) in which there is no pore. The papilla has a well developed protoplast with a large nucleus which is most often found in the projecting portion of the papilla (fig 47). A few abnormal papillae were noted on the mature leaf in which the thick cellulose portion of the wall was only developed at the apex (fig 49). Function of the Papillae.

The specialised nature of the papillae on the leaves of Brunsvigia gigantea and Haemanthus rotundifolius suggest that 13 they have a special function. It is possible that they secrete mucilage which aids in the emergence of the leaves and prevents dessication. Mucilage hairs that come nearest in structure to the papilla© described, are those of Gonocaryon pyriforme. described by Haberlandt I9I4“P*488. The bases of these mucilage hairs are thin-walled, while the projecting upper port­ ions are thick-walled. The lumen of the cell connects directly with a mucilage cap which may be washed away by rain (fig. 1 9 3 A) In the papillae described in this Investigation, it is difficult to see how mucilage secreted by the protoplast could pass through the thick cellulose wall to the exterior. It is of course possible that the inner cellulose wall is formed after the papillae have ceased to function, but no evidence could be found for this. An alternative suggestion is that the outer cuticularised portion of the wall at the apex of the papilla becomes mucil­ aginous, absorbing dew, or water from the atmosphere, this water being drawn into the protoplast through the cellulose wall. Irregular swellings of the cuticularised portion of the wall sometimes occur (fig 48), which tend to support this view. The idea of a water absorbing aerial surface is not new. Wolkens, 1887 describes water absorbing hairs on plants from the Egyptian and Arabian deserts. Halket, I9II suggests that the epidermis of certain species of Salicornia absorbs water which is passed through special spiral cells to the assimilating tissue, (see description of spiral cells of Nerine corusca in Part III. ) Marloth, 1926 found water absorbing hairs on the leaves of several South African plants, especially those that grow under semi-arid conditions, that is, the same habitat as for the plants under consideration. Marloth describes water- absorbing hairs on several plants with prostrate leaves similar to those of Haemanthus rotundifolius and Brunsvigia gigantea. The water absorbing hairs of Briospermum pustulatum. Marl.are similar in structure to the papillae of Haemanthus rotundifolius having thick outer walls and pitted bases, as is shown by comparing Marloth’s figure (Tafel X. 6 4 and fig. 24* Marloth describes an Amaryllidaceous genus Gelhyllis which has water absorbing papillae. 6. villosa, G. longistylis, and G. verrucosa (Marloth Tafel XI. 6-15 ) have hair-cells borne on m ulticellular bases, similar to the hairs of Bypoxis villosa (see Part III fig. 201) and Molineria recurvata. (see Part IÏÏ fig. 198.) However it would seem that in the papillae of Haemanthus rotun­ difolius and Brunsvigia gigantea specialisation has proceeded further than in the plants described by Marloth, that is, in the elaboration of the apex.

It Is hoped that it w ill be possible later to conduct some experiments to determine the function of these papillae. 14

Stomatal variations. The stomatal frequency values increase from the base to the apex of the leaf and from the median line to the margin for both surfaces (fig 50). There is no fall at the apex as in Haemanthus coccineus. The values for the upper surface are much higher and more uniform than the corresponding values for the lower. The index values are much more constant than those of the frequencies but fehe gradients are similar in form, as is well shown by comparing figs5 0 and 51* At the apex of the leaf the epidermal cells of both surfaces are smaller than in the centre of the leaf. The decrease in size of the epidermal cells, see fig52 for the upper surface, and 53 for the lower, causes the closer approximation of the stomata and so higher frequency values. At the base of the leaf the frequency values remain surprisingly high when compared with Haemanthus coccineus. This is especially so for the upper surface fig 5 0 and is due partly to the high index value but more especially to the small size of the epidermal cells and the occurrence of very small cells (fig 56 ) . The great narrowing of the epidermal cells at the base of the lower surface (fig 57) sim ilarly causes a higher frequency value than would be expected. Variations in venation. The parallel veins are not evenly spaced in all parts of the leaf. They tend to be crowded together at the base, along the margins, and at the apex of the leaf. They are furthest apart in the centre of the leaf some distance from the base. These pecularitiea can be correlated with the shape of the leaf, the varying expansion of the tissues, and the thickness of the leaf. The number of transverse commissures per unit area varies in different parts of the same leaf. Thus they are more numerous at the margins than in the centre of the leaf. From the base there is a decrease, followed by an increase at the apex. These pecularities are illustrated by the following table for a mature leaf of Brunsvigia gigantea. TABLE 2 .

Apex No. of Main Veins per No. of transverse com­ o f u n it a r e a . missures per unit area. l e a f , C entre Margin C entre Margin 6 12 15 19 5 9 13 13 5 7 II 16 Base 7 10 23 23 15

Thus the apex and margins of the leaf have more vascular tissue per unit area than the centre and base. HYMSNOCAms FESTALIS. = H. calathina, Nichols. X Elisena longipetala. Herb. Rymenocallis festalis has lingulate leaves. The leaf examined was obtained from Kew Gardens and was 14 inches long and had a maximum width of Iv inches. The leaf has a thick­ ened median region on the lower surface; the ridges dying out towards the apex of the leaf. The stomata are not evenly distributed over the surface of the leaf. Thus the median portion of the lower surface is almost entirely without stomata, especially the ridges already mentioned. Here the epidermal cells are greatly elongated longitudinally, parallel to the long axis of the leaf. The wings of the leaf-lim b have numerous stomata and the epidermal cells are smaller and have rounded ends, as seen in surface view, in shaip contrast to the cells occuring in areas lacking stomata. Counts were made near the median line of the leaf, avoiding the areas without stomata, and along the margins. The frequency values, for both surfaces increase from the base to near the apex where there is a distinct fall as in Haemanthus coccineus. The stomatal index values are more uniform than those of the frequencies, but a distinct gradient of increasing values from the base to the apex of the leaf is found as for the frequencies. The epidermal cells are largest at the base of the leaf and decrease In size towards the apex.

NARROW LEAVE 3 . 1. GALANTHIJ3 NIVALIS.L. The bulb of Gal ant bus nivalis produces only two leaves each season, these being lingulate or linear and much smaller than the leaves already considered, the leaf examined being only three inches long. The material was grown in the Bedford College gardens. The stomatal frequency values for the lower surface (L.S.) are much higher than those of the upper (U.S. ) as seen in fig 58. At the apex of the lower surface there is a considerable area (about 2 sq. mms) entirely without stomata, and along either 16

margin there is a narrow strip (about five cells wide) also without stomata. For the upper surface stomata extend to the apex of the leaf, but there is a comparatively wide strip along either margin (about ^ mm.) w ith o u t stom ata. The l e a f o f Haemanthus albiflos also has no stomata along the margin of the upper surface. An interesting feature of the leaves of Galanthus nlvalifl is the distinct banding of the upper surface. This banding consists of areas with a few stomata very widely spaced and in these areas the epidermal cells are greatly elong­ ated parallel to the long axis of the leaf, followed by areas with numerous stomata and short epidermal cells. Counts were made in a band with numerous stomata, near the median line of the leaf and near the margin. The frequency curves for both surfaces show a rise from the base of the leaf followed by a fall anf rise in the middle and a sharp fall at the apex, (fig 58) These curves are similar to those described by Salisbury 1927 p. 22 for the elongated axes of Juncus effusus. The index values are more constant than those of the frequencies, (fig 58) but the curves have the same general form. At the base of the leaf the epidermal cells are small especially those of the lower surfacè. (fig 6 5 ) There is a gradual increase in size of the cells towards the apex, as is seen by comparing figs6 4 (base), 62. and 60 (near apex) for the upper surface and figs 65 (base), 6 3 , and 61 (near apex) for the lower surface. Thus the high frequency values at the base of the leaf are due to high index values and the small degree of expansion of the epidermal cells causing the close approximation of the stomata. At the apex of the leaf the sharp fall in frequency values is due to the fall in index values, and the comparatively great degree of expansion of the epidermal cells near the apex of the leaf causing the wide spacing of the stomata. At the apex of the lower surface the epidermal cells become very small but no stomata are present. On the upper surface however the stomatal frequency curve continues to fa ll inspite of the small size of the epidermal cells owing to the rapid fall in index values. The frequency values decrease from the median line of the leaf towards the margins and is due to a falling index gradient and decreasing size of the epidermal cells in the direction indicated, as shown in Table III.

TABLE III.

Upper surface. M argin C en tre M argin Stomatal frequencies across leaf. 0 ^ 3 8 ^ 87 78 69 ! 0 1 ...... ! “part of marginal area without stomata included. 17

The Stoma. The stoma Is of the typical Monocotyledonous type. The horn-like projections from the guard-cells as seen in transverse section are not so large as those of the stoma of Haemanthus coccineus. (compare figs 59 & 19) Also the inner and outer horn-like projections are similar in size unlike Haemanthus c o c c in e u s.

11. AimOGHARIS FALCATA (L'HERIT) HERB. Ammocharis falcata produces numerous distichous pro­ strate leaves. The material examined was collected in South Africa. The leaf examined was 6^ inches in length and ip of an inch in width. The stomatal frequency values for both the upper and lower surfaces are surprising high and uniform when c ompared with similar values for Haemanthus coccineus as is shown by t a b le IV. TABLE IV.

Upper surface Lower surface b a se apex d i f f . b ase apex d i f f . Ammocharis f a lc a t a 149 143 6 98 105 r 7

Haemanthus c o c cin eu s 4 43 39 2 42 40 ...... _ . j Thus Ammocharis falcata has no w ell marked frequency gradients. For the upper surface (U.S.) there is a fall in values for a short distance from the base followed by fluctuations about the same mean to the apex (fig 66). For the lower surface (L.S.) there is a similar fall at the base followed by a gradual rise to the apex. The index values for both surfaces are remark­ ably constant except for a slight fall at the apex (fig 67). Considering the variations in expansion of the epidermal cells (figs 68 - 75) there is an increase in size from the base to near the middle of the leaf followed by a decrease to the apex. Thus the fa ll in frequency values towards the middle is due to the increase in size of the epidermal cells as the index values are practically constant. In the same way at the apex of the leaf the increase in frequency values is entirely due to the decrease in size of the^idermal cells causing the closer approximation of the stomata, as the index value tends to fa ll. Thus the expansion factor modifies very considerably the fre­ quency curve as would be determined by the variations in index values alone. 18

The combined action of falling index values and decrease in size of the epidermal cells causes a marked fall in the fre­ quency values from the median line of the leaf to the margin as in the narrow leaf of Galanthus nivalis (see Table V).

Ammocharis falcata. TABLE V.

Stomatal frequencies.

Upper surface Lower isurface Base Near apex Base Near apex Margin 135 125 126 124 36 86 81 82 Centre 137 134 131 135 88 87 84 89

i i i . NARCISSUS POETICUS. L. Narcissus poeticus has a linear leaf with a thickened median area marked by four ridges on the lower surface except at the apex of the leaf where they die out as in Hymenocallis festalis. The leaf examined was 11 inches long and ÿ an inch wide. The material was grown in the Bedford College garden. Counts were made near the median line of the leaf avoiding the ridges on the lower surface as these cause marked irregularities in stomatal distribution; the ridges having very few stomata and elongated narrow epidermal cells.

The frequency values for both surfaces increase from the base of the leaf to near the apex where there is a sharp fall as shown in fig 7 6 . The values also increase from near the mid-rib to the margin as in Haemanthus coccineus and in con­ trast to the other narrow leaves described. The index values are much more constant than those of the frequencies, the irregularities of the latter being almost entirely due to the variations in the expansion of the epidermal cells. This is shown in the figs 77 - 80 for the upper surface, passing from the apex to the base of the leaf. Table VI gives the diff­ erence between the large and small cells at the base and apex of the leaf. 19

Harclaaus poeticus TABLE V I. 1 BASE APEX:

Large c e l l Sm all c e l l Large cell 1 Small cell Upper .6 3 X ,03 ,2 5 X ,0 3 , 1 3 X ,02 ,03 X ,02 su r fa c e

Lower . ,63 X ,03 - ,25 X .02 ,2 2 X .02 .12 X ,02 su r fa c e mms.

Prom the table it w ill be seen that increase in the size of the cells is due almost entirely to longitudinal expansion parallel to the long axis of the leaf, comparatively little change taking place in width as seen in surface view.

Variation in the size of the stoma The stomata show very little variation in size over the individual leaf for all the seven leaves examined. The most noticeable feature is a change in shape when comparing stomata at the apex and base of the leaf for both surfaces. Thus at the apex the stoma tends to be circular as seen in surface view and at the base elliptical. The stomata in the leaves examined are all orientated with the long axis of the pore parallel to the long axis of the leaf. Thus the change in shape of the stoma at the base of the leaf can be correlated with the great longitudinal expansion of the epidermis. 20

SUMMARY.

(I) All the leaves examined showed a stomatal frequency gradient increasing from the base to the apex of the leaf. The gradient may be steep (Haemanthus coccineus) or very slight (Ammocharis f a l c a t a ) . (II) , This gradient is frequently modified by a secondary fall in values at the apex of the leaf for both surfaces. (Haemanthus coccineus. Narcissus poeticus, Galanthus nivalis, Hymenocallis festalis.) In the case of Haemanthus rotundifolius this fall at the apex covers nearly the whole area of the upper surface, the fall in values towards the base prob­ ably occurs in that part of the leaf within the bulb. Marked fluctuations may take place within the general gradient from base to apex as in Haemanthus coccineus and Galanthus nivalis. In other cases there may be a fluctuation about a mean value as in Ammocharis falcata.

(III) A gradient of increasing frequency values from mid-rib to margin is found in the broad leaves examined. In narrow leaves it may occur also (Narcissus poeticus) but more frequently the gradient is reversed, and there is a decrease towards the margin as in Ammocharis falcata and Galanthus nivalis. (IV) The stomatal index values were found in every case to be more uniform than those of the frequencies, but the same general gradients are found, that is an in­ crease in values from the base to the apex of the leaf where there is frequently a marked fa ll, and an increase in values from mid-rib to margin for broad leaves and some narrow ones, and a reverse gradient for other narrow ones,

CV) The stomatal frequency gradients result from the action of two factors:

i. Variation in the proportion of epidermal cells becoming stomata as expressed by the index value. ii. Variation in the degree of expansion of the epidermal cells. 21

Generally the smallest epidermal cells are found at the apex of the leaf and they Increase in size more rapidly along the median line of the leaf compared with the margin as the base is approached. At the base the cells are somewhat smaller than a short distance from the base as, although they are greatly elongated, they have become very narrow. The decrease in the size of the epidermal cells towards the apex and a lesser degree towards the base of the leaf causes an increase in the frequency values as the individual stomata are not so widely spaced as in the centre of the leaf where the expansion factor is a t a maximum. (VI) The expansion factor can be correlated with the water supply to the leaf while it is growing. The base and apex of the leaf are formed first and growth is intercalary. Successive pieces that are added to the leaf-limb each receive a better water supply as the vascular system developes, with the result that the epidermis undergoes greater expansion and so the frequency values fa ll more rapidly than would be ex­ pected from the fall in index values. In the mature leaf the apex and margin of the leaf have undergone less expansion than the mid-rib area and base and this results in a greater extent of vascular tissue per unit area in the former parts.

(VII) Epidermal papillae were found on the upper surface of the prostrate leaves of Haemanthus rotundifolius and Brunsvigia gigantea. The papilla frequency values give similar gradients to those of the stomata. The index formula can also be applied to the papillae in which case the gradients are found to be more constant than those of the frequencies as in the case of the stomata. It is obvious that if the expansion factor affects the stomatal frequency it must also affect the papilla frequency in the same way. The structure of the papillae is described, and their function discussed (VIII) The laws found by Zalenski (1904) for leaves of different tiers of the plant can be applied to the different parts of the individual leaf. Thus the apex and margin of the leaf resemble the leaves of the upper tiers in their small degree of expansion, and the median area and base of the leaf resemble the leaves of the lower tiers.

In the present investigation the gradients found by Salisbury (1927) were confirmed, and have also been found in other leaf types. 22 Description of Figures.

F ig s 1-19* Haemanthus cocoineus. I. Stomatal frequency curves. L. C. ■ Median line of lower surface. L. M. - Margin of lower surface. U. 0. ■ Median line of upper surface. U. M. *- Margin of upper surface, x 2. Stomatal index curves, letter­ ing as in fig I . X f . 3. Stomatal frequencies across leaf at 6 ins. from the base. U. S. = Upper surface. L. S. » Lower surface, x 4* Stomatal indices across leaf as in fig 3. x 5-6. Lines drawn through points with the same stomatal frequency values. 5. Lower surface, x 2 * 6. Upper surface, x 2 * 7-8. Lines drawn through points with the same index values. 7» Lower surface, x i. 8. Upper surface, x 2 . Variations in the epider­ mis of the upper surface from the apex fig 9 to the base of the l e a f f i g 1 5 . X 200. Differences between the epidermis of the upper and lower surfaces. 16. Upper surface. 17- Lower surface, x 200. Structure of the stoma. 18. Upper surface. 1 9 . Lower surface, x 680.

F ig s 2 0 - 3 8 . Haemanthus rotundifolius. 20. Papilla fre­ quencies for the upper surface. Natural size. 21. Papilla in­ dices for the upper surface. Natural size. Figs 22 - 3 0 Structure of the papilla x 680. 22. Papilla in the solid, 2 3 . Longitudinal section of short papilla. 24. Same for a long p a p illa , p ■ p i t t s . 2 5 - 2 6 . Apex of the papilla in the solid. 2 7 - 28. Openings in the apex of the papilla. Figs 29 - 32. 2 9 . Stomatal frequencies for upper surface. Natural size. 30. Same for the lower surface. Natural size. 31. Stomatal index values for the lower surface. Natural size. 3 2 . Same f o r th e upper surface. Natural size. Figs 33 - 38. Variations in the size of the epidermal cells, x 200. 33, 35, 37. Apex centre, and base respectively for the lower surface. 34, 36 38. The same for the upper surface.

F ig s 3 9 - 4 1 . Haemanthus albiflos. young leaf. 3 9 . Stom atal frequencies for upper surface. Shaded areas with stomata, blank areas without. 40. Same for lower surface. No areas without stomata. Natural size. Figs 41 - 42. Epidermis in surface view. X 6 8 0 . 4 1 . Epidermis from "A”, upper surface. 42. Epidermis from "b ", lower surface.

F ig s 4 3 - 5 7 . Brunsvigia gigantea. 43. Papilla frequencies for upper surface, x f . 44. Papilla indices for upper surface, x Figs. 45, - 49. Structure of the papilla, x 680.^ 4 5 . Double - tipped papilla in the solid. 46. Papilla in longitudinal section, a « ring of cellulose, b - mucilage plug, c = apical cap of altered cuticle, d - cellulose wall at apex of papilla. 48. Papilla with peculiar lateral bulge. 49. Abnormal papilla. 23

50. Stomatal frequencies shown as curves for the margin of the upper surface (U.M. ), median lin e of the upper surface (U.O# ), margin of the lower surface (L.M.), and the median line of the lower surface (L.G^), x 51 • Stomatal indices, lettering as in figs 50. X t* Pi63 52, 54, 56. Portions of the upper epidermis passing from the apex to the base of the leaf, x 2 0 0 . Figs 53, 55, 57, the same for the lower surface. % 200.

Pigs 58 - 65. Oalanthus nivalis. 58. Stomatal frequency and index curves for the upper surface (U.S.), and the lower surface (L.S.). Natural sizb. 59. Stoma from the lower surface, x 680. Pigs 60, 62, 64, successive pieces of epidermis of the upper surface from the apex to the base of the leaf, x 200. Figs 61, 63, 65* the same for the lower surface, x 200.

Pigs 66 - 75. Ammocharis falcata. 66. Stomatal frequencies for the upper (U.S.J and lower (L.S. ) surfaces. Natural size. 6 7 . Same f o r th e sto m a ta l i n d i c e s . N a tu ra l size. Pigs 68, 70, 72, 74* successive pieces of the lower epidermis from the base to the apex of the leaf, x 200. Pigs 69* 71, 73* 75* same for the lower surface, x 200.

Pigs 76 - 80. Narcissus poeticus. 76. Stomatal frequencies and indices for the upper (U.S. ) and (L.S.) surfaces, x Pigs 77* 78 , 79 * 80, successive pieces of the upper epidermis from the apex to the base of the leaf, x 200.

Pigs. 81 - 108. The Stoma. Variations in the stoma at the apex and base of the leaf for both upper and lower surfaces, x 3 8 O. 81 - 8 4 . Haemanthus coccineus. 8 5 - 8 8 . Haemanthus rotundifolius 8 9 - 9 2 . Narcissus poeticus. 93 - 96. Hymenocallis fas tails. 97 - 100r Brunswigia gigantea. 101 - 0 I 4 . Ammocharis falcata. 1 0 5 - 108. G-alanthus nivalis. First vertical column, ffigs 8 1 , 8 5 * 89* 93* 97* 101, 1 0 5 * ) stomata from 6pex of leaf, upper surface. Second vertical column, stoma from base of leaf, upper surface. Third vertical column, stoma from apex of the lower surface of the leaf. Fourth column, stoma from base of lower s u r f a c e . 2 4 HAEMANTHUS COCCINEUS Stomatal frequencies to so

U.M.

MO u.c.

30

— »■*'

/3 iBa.% of leof. Distance in inches. F ig .l.

Stomatal indices 40i

50

/o

JBose ofleaf Dis ha nee in inches. /Apex of leaf. F ig .2 . Stomatal frequencies Stomatal indices

4.0

So

, - 3 ÂTTTns / 2 3 SETTHns) »eft rnargrin F ig.3. left rrartjtn F i g , 4 . right mon^n 25

HAEMANTHUS COCCINEUS.

Stomatal frequencies.

Lower surface. Upper surface.

F ig . 5 F i g . 6; 26

HAEMANTHUS COCCINEUS

Stom atal in d ic e s

Lower surface Upper surface

m

50 -

25/

I5Z 129 KO 2lé

K>l

57 HZ

/•8

Fig.S Apex_. HAEMANTHUS C QC CINEUS 1 2.

13.

13. 29 15.

16. Upper surface.

1 7. -JLjOwer_ g i ] ^ f a G A 30 HAEidANTHUS COCCINEUS

Upper surface

Lower surface.

F i g . 19. 31

HAEMANTHUS ROTUNDIFOLIUS

Papilla frequencies

Upper surface

F i g . 20.

Papilla indices

zo F i g . 21. 32

HAEMANTHUS ROTUNDIFOLIUS.

r

F i g .24.

ig .2 5 . F ig.26 F ig.27, F ig.28 HAEMANTHUS ROTUNDIFOLIUS 33

Stomatal frequencies.

Upper surface

F i g . 29

Lower surface

20 2 0

20 zo

F i g .30. 34 HAEMANTHUS ROTUNDIFOLIUS

Stomatal index.

Lower surface.

20t

F i g .3 I .

Upper surface.

F ig .3 2 3 0 35

HAEMANTHUS ROTUNDIFOLIUS.

Apex. Lower surface.

F i g . 33.

Apex. Upper surface.

F i g . 34. 36

HAEMANTHUS ROTUNDIFOLIUS

Centre. Lower surface.

F ig .3 5

Centre. Upper surface

F ig .3 6 . 37

HAEMANTHUS ROTUNDIFOLIUS.

Base, Lower surface.

Base, Upper surface

F ig ,3 8 . 38 HAEMANTHUS ALBIFLOS

Stomatal frequency.

Upper Lower s u r fa c e s u r fa c e

Iko

F i g . 39. F i g . 40.

A B

F ig .41. F ig .42. 39

BROTSVIGIA GIGANTEA

PAPILLAE.

Freguencies. Indices.

8 2, /o s 8 6 /o o

9-8

F i g . 43 F i g . 44 40

BRUUSVIGIA GIGANTEA.

pa pilla e

F i g . 48

P i g . 45.

F i g . 47 F i g . 4 9 . 41

BRUNSVIGIA GIGANTEA

Stomatal frequencies.

A.0 / /

l.M.

20

V)

JO j^istance i-n inches. Apex.

Stomatal indices. 4 0

UÆ

B ase /o F i g . 51 Distance in in ch es. 42

BROTSVIGIA GIGANTEA

Base. Apex.

F i g . 56. F i g . 54 F i g .52

0

F ig .55 F ig .53 43

GALAHTHUS HIVAIIS.

Utû

/20 i.S. /JO F i g . 60.

F i g . 61. as.

60

F i g . 62.

F i g . 63. Distance in cm s. Apex. F i g . 58.

F ig .59 F i g . 65. 44 AMMOCHARIS FALCATA.

Stomatal frequencies.

m

U.3.

CO

l>stQ ncc in i nc he s

Stomatal indices.

X>istanee in Inches. 45 AMMOCHARIS FALCATA

:E

F i g . 68, F i g . 69.

F i g , 70. F i g . 71.

F i g . 72. F i g , 73.

F i g .74. F ig .75 46 NARCISSUS POETIC US.

60

40

IS ij.a

Base é 8 /o^ ^ Distance in inches, (^a/c //n^ F i g . 76.

Upper surface.

F i g . 77. F i g . 79.

F i g .78. F ig ."80. 47 THE STOMA

Haemanthus coccineus.

81 82. 83 84.

Haemanthus ro:undifolius.

85 86 . 87. 88 Narcissus poe

89 90. 91 92 Hymenocallis festalis

93 9 4. 95. 96 Brunsvigia gigantea.

98 99 ICO Ammocharis falcata.

ICI 102 103 104

Galanthus nivalis

105. 106. 107. [08 48

PART II.

THE ANATOMY OF THE DORMANT LEAF, AND OF THE LEAF AT VARIOUS STAGES OF GROWTH WITH SPECIAL REFERENCE TO MERISTEMATIC ACTIVITY AND THE VASCULAR SYSTEM.

NARCISSUS POETICUS. L.

&

COMPARISON WITH N. ELVIRA.

Introduction.

If* "bulbs of Narcissus poeticus.L..are examined in the early spring, when the leaves are an inch or so above the ground, it is obvious that the tips of the leaves are mature, and that subsequent growth causing elongation of the leaves takes place in that part of the leaf which is hidden in the bulb, and protected by a large number of closely packed fleshy scales. Careful marking of the leaf surface above the ground w ill show that very little increase in the size of the exposed surface occurs, and transverse sections of the leaf show that all the tissues are mature.

Brief reference to this basal growth is made by Arber 1 9 2 5 in her book, "Monocotyledons" p. 92. Only a general statement is given that "there is often a strong tendency to cell division towards the adaxial surface of the leaf-base , and petioles, and a slight tendency to the same activity towards the abaxial surface."

In the present investigation a study has been made of the anatomy of the mature leaf and of the growing zones in the lower portion of the emerging leaf. Special attention has been given to changes which occur in the epidermis and mesophyll during the change from the meristematic condition to maturity, and differentiation of the vascular bundles in the growing zone during the elongation and maturation of the leaf have been part icularly studied. 49

In the following account the structure of the leaf in its dormant condition ( in the resting bulb) will be described first. The resting bulb consists of a series of fleshy con­ centric scales, developed from bases of foliage and scale leaves, enclosing a shoot which is from 3 0 mms. to 4 5 mms. in length (fig 109/. The shoot is composed of two to three scale leaves which never develop normal leaf-lim bs, and three to five foliage leaves, four being the usual number. These foliage leaves, although completely covered by fleshy scales, have green tips, the lower portions being yellowish or white. The leaves are distichous, and each consists of a linear, parallel-veined lamina (called by Arber a "Pseudo-lamina. " ) with a well defined mid-rib, and a sheathing leaf-base. The sheathing leaf-bade of the outer leaf encloses the bases of all the inner leaves, and in the same way each of the inner leaf-bases encloses the lower portions of a ll the leaves within it, except the innermost leaf which is non-sheathing and bears in its axil the flower for the current year. The bud that gives rise to next year's scale and foliage leaves and flower, is terminal on the stem axis as shown in fig I3 I. See also Irmisch 1850 and Goebel 1905, vol I I p . 299.

SECTION I . PRIOR TO THE RESTING STAGE.

The development of the young leaf prior to the resting stage was followed in Narcissus bulbocodium. L.var. citrinus and Haemanthus alb iflos. Jacq.

The leaf prlmordia appear in acropetal succession on the meristematic stem apex and are distichous in both plants ex­ amined. The apex of the leaf-limb is formed first by a local bulge on one side of the stem apex. Later the leaf-base is formed by the extension of the meristematic tissue to encircle the stem axis (amplexical). Meristematic activity ceases first in the apex of the leaf-lim b and this proceeds bas ipet ally, but involves only the central tissues of the base of the leaf-limb, the peripheral tissues remaining meristematic. Auxesis also proceeds bas ipet ally but very little extension of the tissues of the lower half of the leaf-limb takes place before the resting stage. In the leaf-base meristematic activity ceases prior to the resting stage and considerable auxesis follows. With the cessation of meristematic activity comes the laying down of starch within the tissues, that is, in the mesophyll of the leaf- base, and the central mesophyll tissues throughout the leaf- limb. The greatest accumulation of storage starch is found in the leaf-base, and the base of the leaf-limb.

A procambial strand is differentiated early in the elong­ ated leaf primordium before the leaf-base has been formed. 50 After the tissues of the leaf-base have been laid down a few narrow elongated annually and spirally thickened tracheids are formed in the leaf-lim b. The tracheal tissue continues with­ out interruption to the stem system but the tracheids become short and more numerous especially in Haemanthus albiflos where at this stage the leaf has a total length of 2 mms. In Narcissus bulbocodium var. citrinus lignifled tissues were found in a young leaf only 1 mm in length.

Before the leaf passes into the resting stage the tissues at the apex of the leaf-lim b have differentiated and are mature. This is followed by a extensive zone at the base of the leaf- limb consisting of immature tissues. The small leaf-base is non-merlstematic but the individual cells are very small.

SECTION I I . THE DORMANT LEAP.

The outer foliage leaf of a well formed shoot removed from a bulb in the resting condition measured 3 0 mms. in length. This is small for the main shoot from the central bulb of a "mother group." The leaf w ill be considered in three portions, namely, the leaf-base, the growing zone at the base of the leaf-lim b, and the mature upper portion of the leaf-lim b. The completely sheathing leaf-base was about 9 mms. in length, ( f i g s 109 & n o ) . That portion of the leaf-base which con­ tinues up into the leaf-limb is termed In this account the LEAF-BASE PROPER. The portion of the leaf-base which completes the sheath is termed the SHEATHING PORTION. It becomes thin in the upper part where it terminates in a crescent-shaped ridge 3 mms. in length. The leaf-limb consists of a basal growing zone about 1 4 mms. in length, and a small mature apical portion about T mms. in le n g t h .

The leaf-base. (i) The Epidermis.

The epidermal cells at the lower end of the sheathing leaf-base are elongated parallel to the long axis of the leaf, being three or four times as long as broad, seen In surface view, (fig 112). The cells of the epidermis covering the adaxial and abaxial surfaces of both leaf-base proper and sheathing portions are similar in size and shape. There is no cell division at this level, but auxesis is contlnously taking place from the time growth commences. The cell walls are thin, the protoplasm contains relatively large vacuoles, and the nuclei are comparatively small. Starch is never found in the epidermis at any stage except in mature guard-cell s. In the centre of the leaf-base the epidermal cells are hexagonal with only a slight tendency to become elongated, as seen in surface view, (fig II3 ) 5L

The nuclei are large, the protoplasm is dense, (Contrast the two cells drawn in detail in figs 1 1 2 and I I 3 respectively), and only a few cell divisions take place. In the upper part of the leaf-base the adaxial and abaxial epidermis of the leaf- base proper (that part which continues up into the growing aone) is composed of small meristematic cells (fig II5 ) . The cells have thin walls, large nuclei, and dense granular pro­ to p la sm .

The epidermis of the sheathing portion is also small- celled in the upper part, especially that of the crescent-shaped ridge, but comparatively little cell division takes place.

(ii) The ground-tissue of the leaf-base. The cells of.the ground-tissue are rounded as seen in transverse section with large air spaces between the individual cells. In longitudinal section the cells are rectangular, a few being elongated parallel to the long axis of the leaf as in fig 114* The cell walls are thin, the nuclei small, and the protoplasm is scanty. These cells are densely packed with storage starch. No cell divisions take place but there is a certain amount of auxesis. Rows of elongated cells are present which contain raphides.

Towards the upper part of the leaf-base proper a change takes place in the cells of the peripheral ground tissue. The starch grains become smaller and fewer in number, and some cell divisions take place (fig 116). This tendency increases until the true meristematic region of the growing zone is reached. This is most clearly seen in the two sub-epidermal layers of the adaxial and abaxial surfaces.

The Growing Zone at the base of the leaf-lim b.

( 1 ) The E p id erm is. At the base of the growing zone the adaxial and abaxial cells are meristematic, but in the dormant leaf cell division has been suspended. The cells however have all the character­ istics of meristematic tissues. The cells are small with thin walls and ciortain dense granular protoplasm with only a few small vacuoles. The nuclei are large in proportion to the size of the cells. Between 10 and 12 mms. as measured from the base of the shoot, cells divisions result in the production of daughter cells of similar size, but at 1 3 mms. c e r ta in sm all narrow cells are readily distinguishable, both in surface view and longitudinal section (figs1 1 7 & 1 1 8 ). 52

These small cells are the stomatal initials. From this level cell division ceases, (except in the case of the stomatal initials) and is followed by extensive auxesis. The epidermal cells increase in size chiefly by elongation parallel to the long axis of the leaf (fig. 119). The stomatal initials which have also increased in size, becoming practically square as seen in surface view, now divide by longitudinal walls parallel to the long axis of the leaf, so that two guard-cells are formed (fig 121). This does not take place in all the initials simultaneously, but in a transition zone at the upper end of which all the Initials have divided but those Initials that are in advance of the others have the guard-cells greatly increased in size. The guard cells bulge into the neighbouring epidermal cells as they mature. The median portion of the middle lamella between the two guard-cells now dissolves away and a pore is formed. No signs of starch could be found in the guard-cells prior to the formation of the pore. At 25mms from the base of the shoot the epidermal cells and stomata are mature, the epidermal cells being about ten times the length of the original meristematic cells and two to three times as wide (fig 1 2 3 ). The mesophyll.

Meristematic activity in the mesophyll of the growing zone is confined to the three or four sub-epidermal layers of the adaxial and abaxial surfaces. The central mesophyll undergoes no cell division, and contains abundant storage starch. Thus the statement in Arber's "Monocotyledons" 1925 , that as a rule cell division affects the mesophyll only needs modifying as it affects only the peripheral mesophyll in the plants investigated in Part 11.

(ii) The palisade forming zone. The sub-epidermal cell layer of both the adaxial and abaxial surfaces gives rise by meristematic activity to the palisade. The cells divide by walls in two planes only, that is in the plane of the longitudinal section and at right angles to it (fig 118). In the upper part of the growing zone cell divis­ ion ceases and is followed by auxesis of the individual cells. At the level of fig 124 the palisade cells have nearly reached their full size. These cells are somewhat modified as they occur in the narrowed and rounded apex of the leaf.

(iii) The sub-palisade zone. A layer about two cells deep beneath the palisade of both surfaces shows some meristematic activity at the base of the growing zone. Passing hijgher up this soon ceases and is follow­ ed by expansion of the cells which become elongated parallel to 53 the long axis of the leaf (fig 124). These cells have less chlorophyll content than the palisade. (ivi The ground tissue of the growing zone.

At the hase of the growing zone the ground tissue is composed of small thin-walled cells packed with storage starch and similar to the ground tissue of the leaf-base. Proceeding up­ wards the cells become larger, being rectangular and elongated parallel to the long axis of the leaf, as seen in longitudinal section (fig 126). The cells increase in size by auxesis so that in the upper part of the growing zone they are three to four times the dimentions of the original cells.

The mature upper portion of the leaf.

The mature portion of the leaf-limb is small consisting of the apical five to seven, mms.

(i) The epidermis.

In longitudinal section the elongated epidermal cells can be seen to have thick walls especially the outer ones and those abutting on the palisade. The cuticle is comparatively thin and smooth (fig 124) # The stomata are sunk below the surface of the epidermal cells. The overarching of the ridges from the guard-cells gives the pore an hourglass form as seen in trans­ verse section (Wassermann 1924)*

(ii) The palisade layer. The palisade cells are similar at both surfaces, being rectangular, and only showing a small degree of expansion at right angles to the surface owing to the rounding of the apex of the leaf, while the subsequent intercalary portions of the leaf- limb have larger palisade cells. The small expansion of the mesophyll and epidermal cells at the apex of the leaf compared with the rest of the leaf-limb can be correlated with the reduced water supply compared with the mature leaf (see Part 1 page 7).

(iii) The sub-palisade layer. The cells are small and rounded as seen in transverse section and contain gome chlorophyll, but much less than the palisade. Inspite of their small size these cells are mature.

(iv) The central ground tissue. The ground tissue is composed of rectangular cells as seen in longitudinal section. The cells are rounded as seen in 54

transverse section. They contain some starch (fig 127) but no further expansion takes place, as these cells do not collapse in the mature leaf, as they are in the apex of the leaf.

The vascular system. A large number of vascular bundles (about 30) pass from the stem of the bulb into each leaf as shown in fig 131, those passing into the sheathing portion of the leaf-base die out at the apex of the sheath, those passing into the leaf-base proper continue through the limb of the leaf to the apex. At the base of the leaf-limb the vascular bundles pass through a region of the leaf which w ill later undergo great elongation, during the growing period when the tissues are rapidly expanding. In this region the xylem has only one or two protoxylem elements d iff­ erentiated in the form of annular or spiral tracheids, thus being capable of water conduction to the maturing leaf apex and allowing at the same time of expansion during the elongation of the immature zone. At the leaf apex (fig 130) and in the leaf- b a se ( f i g 1 3 2 ) the metaxylem is also lignified, these regions undergoing very little subsequent expansion. The metaxylem of the immature zone (zone of expansion) is unlignified, (figs 133 & 1 3 4 ), the young tracheids containing at this stage considerable cell contents, and being unable to conduct water, as can readily be demonstrated by placing leaves in eosin.

The inverted bundle system.

The dormant leaf has a system of inverted bundles just below the adaxial surface of the leaf-limb. This system con­ tinues from the leaf apex into the upper part of the leaf-base, where it ceases abruptly. The inverted bundle system does not therefore connect directly with the vascular system of the stem, and its only connection with the normal vascular system (which does connect directly with the stem system via the leaf-base) is by means of commissures rising from the dorsal and ventral sur­ faces of the leaf and connecting the two systems. In the dormant leaf the inverted bundles have very little differentiation (figs 128 & 1 2 9 ), the xylem is unlignified, the phloem undiff­ erentiated, but a few s cl ere nchy matous elements are present.

In the dormant leaf the bundle systems are connected by undifferentiated transverse commissures passing from the phloem of the individual bundles (fig 128). This allows great exten­ sion in growth without rupture of any tissues. 55

SECTION 3. THE HALF-CROWN LEAF.

Throughout the growing season the leaf is continously increasing in length due to auxesis of the tissues laid down in the dormant leaf, and to the meristematic activity of the epidermis and peripheral mesophyll at the base of the leaf- limb. The rate of elongation is not equal in all parts of the leaf. The outer leaf of a half-grown shoot was 183'mms. in length, that is, 5 times the length of the dormant leaf. The sheathing base was 20 mms. in length, that is, a little more than twice the length of that of the dormant leaf, and the leaf- limb was about 163 mms. in length, or six times the length of that of the dormant leaf.

The mature portion of the leaf-lim b which appears above ground transpires at a considerable rate. Two plants of Narcissus Elvira (= Narcissus poeticus, L. var orna tu s X N. tazetta, L. ) whose leaves had reached about half their final length were set up in the laboratory and the rate of trans­ piration obtained by weighing. Each plant lost on an average 0.8 grms. of water per 100 sq. cms. of leaf-surface in 24 hours (see Table VII).

TABLE V I I . Transpiration of water by half-grown leaves of Narcissus Elvira.

Total area of leaves ' Amount o f w ater t r a n s ­ for both surfaces. pired by 100 sq. cms. of leaf surface in - 2 4 h o u r s .

P la n t A. 1 4 6 . 5 s q . cms. • 8 8 5 grm s.

P la n t B. 2 8 4 .2 5 " • 995 ”

The extensive mature portion of the leaf-limb during the growing period depends entirely on the small number of lig ­ nif ied tracheids passing through the extensible immature zone for its water supply. 56

The Leaf-base.

( i ) The Ep Iderml s . The epidermal cells continue to increase in size by auxesis, mainly in the direction of the long axis of the leaf. Cell division does not take place.

(ii) The Ground-1issue.

The cells of the ground-tissue of the leaf-base are small as in the dormant leaf (compare figs 142 & 125) and in both cases are densely packed with storage starch. In transverse section the large air spaces which occur between the cells are con­ spicuous (fig 135).

The Growing Zone at the base of the Leaf-limb. 4 As in dormant leaf this zone consists of a small basal meristematic region, followed by an extensive zone of auxesis which gives place higher up to mature tissues. Meristematic activity affects the peripheral tissues only, the central mes­ ophyll responding to elongation by auxesis of the individual cells which were laid down in the dormant leaf.

(i ) The -Epidermis.

The meristematic activity in the epidermis is mainly confined to the formation of stomatal in itials, and their sub­ sequent division into two guard-cells. However some divisions take place independently of this, increasing the number of epidermal cells as shown in fig 136. About the same proportion of stomatal Initials are found in both the adaxial and abaxial epidermis (figs I3 8 & 1 3 9 ). The region with stomatal initials is followed by a trans­ ition region in which the initials divide to form two guard-cells as in the dormant leaf. The epidermal cells continue to undergo auxesis. The outer walls become greatly thickened, a compar­ atively small portion of the wall becoming cuticularised, as is shown by comparing figs 4 I 0 and I 4 I.

(ii) The palisade layer. Meristematic activity in the sub-epidermal layer starts in the upper part of the leaf-base and continues for about 15 mms in the base of the leaf-lim b. The divisions are rapid and the cells formed are narrow with no air spaces between them (figs 1 3 8 & 1 3 9 ). Auxesis takes place slowly (fig I4 0 ), the palisade cells develop rounded ends as seen in longitudinal section and large air spaces are formed between the individual cells and beneath the stomata (fig 141)* 57

(111) The suh-pallsade zone. A few cell divisions take place at the base of the leaf- limb in this zone (fig 1 3 9 ), but these cells keep pace with the palisade mainly by auxesis. The cells are rectangular as seen in longitudinal section becoming elongated parallel to the long axis of the leaf as they mature (fig 1 4 4 ). (iv) The ground-tissue.

The auxesis that takes place in the central ground- tissue from the base of the growing zone to the mature upper part of the leaf-limb is conspicuous in the half-grown leaf. Comparison of figs 143 and 145 shows that there has been a linear increase parallel to the long axis of the leaf equivalent to ten times the length of the cells in the storage region. As already stated the leaf-limb of the half-grown leaf is six times the length of the leaf-limb of the dormant leaf. Thus it is obvious that the central tissues can keep pace with the elongation of the leaf by auxesis of the individual cells that composed the dormant leaf. In passing from the base to the upper part of the growing zone starch gradually disappears in the cells of this tissue.

The mature apical portion of the leaf-lim b.

(i) The epidermis.

The elongated epidermal cells have regular walls. The outer walls are strongly thickened.

(ii) The palisade.

Comparison of figs I3 8 and 14% show the great extent of auxesis of the meristematic cells that takes place in the formation of the mature palisade cells. The individual cells may be elongated parallel to the long axis of the leaf (fig 147) with large air spaces between them, or have their greatest elong­ ation at right angles to the leaf surface. This is also seen in the palisade cells of similar portions of the leaf-limb of N. Elvira (fig 149)# Frequently the palisade cells are oblique with respect to the epidermis (fig I4 8 ) instead of at right angles. Similar palisade is described by Meyer (1923) in Das Tropische Parenchym pages 7 and 8. (iii) The ground-tissue.

The cell layers beneath the palisade consist of rect­ angular cells elongated parallel to the long axis of the leaf as seen in longitudinal section. In transverse section large air spaces are seen between the individual cells. Many of the thin-walled cells of this central tissue collapse (fig I4 6 ) w hich 58

results in the reduction in thickness of the leaf. No starch is present anywhere in the ground-tissue at this level.

The vascular system.

In the leaf-base the vascular system is similar in the half-grown leaf to that of the dormant leaf, that is, the small and large bundles all have lign if ied xylem but the phloem is not differentiated (fig 150). Undifferentiated transverse comm­ issures connect the phloem of the individual bundles. The xylem is extensive as is shown for the bundle illustrated in fig I5 0 . P assing into the extending zone the amount of xylem becomes reduced (fig 151 ) but the phloem is fully differentiated. The tracheids have a linear arrangement as seen in transverse sect­ ion in contrast to the xylem of the bundles in the leaf-base, and mature leaf-lim b. The tracheids have annular or spiral thickenings and so are capable of extension and at the same t ime of conducting water to the mature leaf-limb. The extent of lignified tissue in the growing zone of the half-grown leaf is much greater than in the dormant leaf (compare figs 5 II & 1 3 3 ) enabling a more efficient supply of water to the much greater extent of mature leaf-lim b.

Passing out of the growing zone the amount of xylem in the vascular bundles increases. The tracheids that are the last to be formed differ in character (fig 152) being smaller in cross section and hexagonal in form (Arber 1925 p. 81). Accompanying this is the development of a certain amount of secondary phloem.

Similar changes in the vascular bundles from the leaf- base to the leaf tip are found in half-grown leaves of Narcissus Elvira. In the leaf-base there is a elongated taass of xylem as seen in transverse section (fig 155) # Passing into the base of the leaf-limb only part of the xylem is lignified, at least half of the xylem consisting of short tracheids with some cell contents and normal"nuclei (fig 156). There is no sign of development of secondary tracheids at this level. In the upper part of the growing zone all the metaxylem tracheids become lignified and small secondary tracheids are formed as in N. poeticus (fig 1 5 7 ). In the mature upper part of the leaf-limb there is a series of small inverted bundles beneath the adaxial surface, these are fully differentiated (fig 154). As these bundles pass into the growing zone only one or two traclfel elements are lignified, and the phloem is undifferentiated (fig 153) • The inverted bundles pass into the upper part of the leaf-base where they die out in the general mesophyll. These inverted bundles are connected with the normal system by transverse commissures which are without lignified tracheids in the base of the leaf- limb. Thus the inverted bundle system cannot be concerned in the conduction of water from the stem throughout the leaf and 59 so probably functions as a water resevoir at least until the leaf is fully grown.

In the mature upper part of the leaf-lim b the two vascular systems are connected by transverse commissures containing lignified tracheids, in contrast to the immature connections in in the growing zone and the leaf-base.

SECTION 4 . THE mTURE LEAF.

The meristematic activity in the base of the leaf-limb of the half-grown leaf is considerable but oubaoquont in subsequent growth this activity declines and finally ceases being replaced in the last stages of growth by expansion of the tissues at the base of the leaf-limb. The leaves finally reach a length of about 350 mms., that is, ten times the length of the dormant leaf. The leaf-base has then reached a length of three times that of the dormant leaf (compare figs 109 & 158) and the leaf- limb twelve and a half times the length of that of the dormant l e a f . N. Elvira differs from N. poeticus in that the leaf-base does not increase greatly in length until the leaf-limb begins to wither and the base is about to form a bulb scale. Thus when the leaf is fully mature the base is only one and a half times that of the dormant leaf while the leaf-limb is about thirteen and a quarter times that of the dormant leaf. All the leaves so far described were the outer leaves of the shoot. The bases of the inner leaves are progressively smaller as seen in figs 159 to 161. The crescent-shaped ridge of tissue of the outer leaf reaches a final length of 12 mms. ( f i g 1 5 8 ) while in the case of the second leaf it only reaches 4 mms. in length. In the third leaf it is absent, the apex of the sheathing portion being concave. The innermost leaf is non­ sheathing, having only a ridge of tissue along either margin (fig 161). The tissues of the mature leaf need no separate description as they have already b^"described in dealing with the mature portions of the half-grown leaf. A portion of the peripheral tissues is shown in transverse section in fig 162. The epidermal cells have very thick inner and outer walls. The stomata are similar in structure to those of Haemanthus coccineus described in Part I p.8. The palisade is similarly developed all round the leaf-limb consisting of a single layer of elongated cells. At the apex of the leaf the mesophyll cells are nob so large as in the rest of the leaf-limb and the palisade layer is not clearly differentiated from the two sub-palisade layers. The central mesophyll is small in amount and not disturbed or compressed as in the rest of the leaf-lim b. Large vascular bundles occur mid-way between the 6 0 upper and lower epidermis as sedn in transverse section, of these the median one is the most pro minant (fig 164/. Somewhat nearer the abaxial surface are smaller bundles, while beneath the adaxial surface are small bundles showing inverted orientation. In all these bundles the xylem is well differentiated and second­ ary tracheids are present which are smaller in diameter than the primary ones. The phloem consists of sieve-tubes and companion cells, both of which have thick cellulose walls (fig 164). Each bundle has a conspicuous starch sheath. Areschoug (1873-8) gives a detailed description of the mature leaf of N. poeticus in his "Ofver Bladets Anatomi". This account is illustrated by eleven text figures.

SECTION 5 . COMPARISON OF THE GROWTH OF LEAVES OF NARCISSUS WITH THOSE OF GALANTHUS NIVALIS,L. AND ' ZEPHYRANTHES CANDIDA, HERB.

Galanthus n ivalis and Zephyranthes Candida resemble Narcissus poeticus in that the increase in length of the leaf- limb from the resting stage to maturity is due to the activity of tissues at the base of the leaf-limb. This is made possible by the protection of the immature tissues by the bulb scales, only the fully mature upper parts of the leaf-lim bs emerging from the bulb, and appearing above ground. As in Narcissus the growing zone consists of a relatively small portion at the base where the peripheral tissues are meristematic, followed by an extensive zone of auxesis, where the cells reach their full size. The central ground tissue keeps pace with the peripheral tissues by auxesis of the cells laid down in the dormant leaf, with the result that the cells of this tissue are large in the mature leaf, As in Narcissus the growing zones have no clearly marked lim its. Above, it fades out as the mature tissues of the leaf-limb become established and below, it dies out in the upper part of the leaf- base. In Zephyranthes Candida adaxial inverted bundles are pres­ ent as in Narcissus, but they are absent in Galanthus nivalis. The changes that take place in the vascular bundles in passing through' the growing zone are similar in Zephyranthes Candida (figs 323 to 325), and Galanthus nivalis to those described for Narcissus. In the greater part of the leaf-base the xylem is lignified, but towards the upper end the last formed metaxylem tracheids are unlignified. In the growing zone of a leaf a few inches in length, only the protoxylem elements are lignified, the metaxylem consisting of large cells with thin cellulose walls and considerable cell contents. 61

As the mature tissues of the leaf-lim b are reached the meta­ xylem becomes lignified and the vascular bundles are found to be fully mature throughout the rest of the leaf-limb. During growth the xylem in the growing zone gradually becomes lig ­ n i f i e d .

The growth of leaves of Brunsvigia gigantea is entirely confined to the base of the leaf-lim b as was found by marking young leaves and measuring at frequent intervals. The mode of growth is probably very similar to that described for Narcissus p o e t ic u s .

SECTION 6 . ANATOMY AND GROWTH OF THE SCALE LEAF AND COMPARISON WITH HAEMANTHUS ALBIFLOS.

The outer three or four members of the shoot of Narcissus poeticus are scale leaves, each of which consists of a flask-shaped base the lower part of which remains enclosed in the bulb and contains abundant storage starch while the upper part appears above ground and is found sheathing the bases of the foliage leaves. In the mature scale the leaf-limb rudiment is indicated by the convex form of the upper part and the curvature of the main veins towards the centre as shown in f i g 1 7 0 for N. Elvira. The upper part of the scale has some chlorophyll located mainly in the mesophyll above the main veins and in approximation to the stomata which results in the position of the stomata being vis able with the naked eye as green dots. At the end of the season the leaf-limbs of the foliage leaves and the upper parts of the scale leaves become cut off by absciss layers.. The portions thus cut off wither, but do not separate cleanly from the living tissues of the leaf-base, pieces of dried tissue remaining attached (fig 171). Usually several absciss layers are formed one below the other so that only the lower part of the base of each member forms a bulb scale. Absciss layers with cork formation were described by Parkin 1898 for Nar cissus pseudo-narcissus, and N. poeticus also for Galanthus nivalis and two species of Leucojum.

In Haemanthus albiflos, Jacq. only foliage leaves are present. Each season two foliage leaves are produced (fig 173 a & b). At the end of the season the leaf-limbs are cut off by absciss layers (figs 174 & 175) and the leaf bases form inner bulb scales, which contain abundant storage starch (fig1 7 3 c & d). Towards the end of the second season, a second absciss layer is formed lower down in these scales, and is circular in contrast to the former. After the upper portion of the scale has fallen away a circular scar is left. The scale then forms an outer bulb scale in the third season (fig 1 7 3 e & f ) . Starch quickly disappears from its tissues and towards the end 62 of that season it begins to wither. Finally in the fourth season it becomes brown and membraneous quickly fallin g away from the bulb (fig 173 g). In Narcissus the bases of the scales and foliage leaves of the previous season form the chief bulb scale members fbr the current season when they contain abundant starch. In the following season they are found towards the outside of the bulb and contain very little starch. In the fourth season they be­ come brown membraneous scales and soon fa ll away form the bulb.

The development of the scale leaf. If a bulb is examined when the tops of the foliage leaves have started to wither the vegetative bud that w ill form next year's shoot w ill be found to be about 18 mms. long (fig 166). The conspicuous outer members of the bud are scale leaves, the innermost encloses a hump of tissue about 2 mms. in length that will give rise to the foliage leaves. The outer scale leaf of the bud examined consisted of a flash-shaped base 11 mms. in length, and a rudimentary leaf-limb 7 mms. in length. Later, development takes place in the base, so that when the scale has reached its greatest size the rudimentary leaf-limb can only be recognized by the shape of the apex. The young scale leaf prior to the resting bulb stage.

(i) The epidermis.

The epidermis consists of rectangular cells elongated parallel to the long axis of the scale as seen in surface view. In the epidermis of the upper part of the scale fully formed stomata are present (fig 167)# (ii) The ground-tissue.

The ground-tissue consists of small rounded cells with large air spaces between them. These cells are densely packed with storage starch (fig 168). During the growing season the cells expand and the starch becomes used up. This is later re­ placed when preparations are made for the formation of a bulb scale. Fig 169 shows cells of the scale base when the apex has started to wither and here the individual cells and starch grains are much larger than those of the immature scale leaf.

(iii) The vascular system. Only normally orientated bundles are present in the scale leaf. No inverted bundles are ever found in the scale leaves at any stage of development. A vascular bundle with lignified tracheids from a young scale leaf is shown in fig 172. 63 SUMMARY

I. The growth of leaves of Narcissus poetlcus, L. Is described, and compared with the growth of those of N. E l v ir a .

II. A brief description is given of the leaf prior to the resting stage for Narcissus bulbocodium, L. var. citrinus Bak. and Haemanthus alb iflos, Jacq.

III. A detailed description is given of the dormant leaf of Narcissus poeticus. The leaf consists of a completely sheathing leaf-base, a growing zone at the base of the leaf-lim b, and the mature apical portion of the leaf-lim b.

IV. The leaf-base of the dormant leaf consists of an epidermis of elongated cells, which do not divide but undergo auxesis, and mesophyll tissue of small cells con­ taining abundant storage starch.

V. In the upper part of the leaf-base there Is a gradual change to the immature growing zone at the base of the leaf-lim b, where the following regions can be dis­ tinguished.

(i) The epidermis is meristematic at the base of the growing zone, but in the upper part of this zone auxesis of the cells is dominant. Stomatsil in it­ ials are formed in the meristematic portion, and these divide to form two guard-cells.

(ii) The sub-epidermal layer is meristematic at the base of the growing zone and the palisade cells are formed with undergo extensive auxesis at a higher level. (iii) The two sub-palisade layers show less meristematic activity than the palisade layer. (iv) The general ground tissue at the base of the grow­ ing zone is similar to that of the leaf-base, that is, the cells are small and contain abundant starch, and are not meristematic. At a higher level the cells of this tissue undergo extensive auxesis to keep pace with the combined meristematic and auxesis activity of the peripheral tissues. The central ground tissue shows no meristematic act­ ivity in any part of the leaf, from the stage of the dormant leaf.

VI. A small portion of the apex of the dormant leaf is mature, and here the epidermis has thickened outer walls and sunk stomata of the typical monocotyledonous type. 64 The palisade is fully differentiated, but the individual cells are small owing to the rounding of the apex of the leaf. The central ground tissue consists of fully developed cells which contain a few very small starch g r a in s .

VII. In the leaf base, and the apex of the leaf-limb of the dormant leaf the xylem in the vascular bundles is fully lignified. In the growing zone at the base of the leaf- limb only the protoxylem is lignified and capable of con­ ducting water, the metaxylem consisting of immature tracheids with thin walls and considerable cell contents. VIII. The inverted bundle system consists of strands of procambium except at the apex of the dormant leaf where differentiation takes place. The transverse commissures are undifferentiated in the leaf-base and growing zone,

IX. The half-grown leaf shows the same regions as the dormant, leaf with the following differences : -

(i) The extent of mature leaf-limb is much greater, and the rate of transpiration has increased.

(ii) The meristematic activity of the peripheral tissues in the. growing zone is not so great.

(iii) In the growing zone the vascular bundles have more lignified tissue to supply the greater extent of mature leaf-lim b. (iv) In the intercalary portions of the leaf-limb, added after the dormant leaf stage, secondary xylem and phloem is present in the vascular bundles. The secondary xylem tracheids are smaller than those of the primary.

X. A brief description is given of the mature leaf.

XI. Similar growing zones, adding intercalary portions to the leaf-lim bs, are found in the leaves of Zephyranthes Candida and Galanthus n ivalis.

XII. The anatomy of the young and mature scale leaves is described and compared with the scale leaves (= bases of foliage leaves) of Haemanthus albiflos. The scale leaf consists of a leaf-base with a tiny leaf-limb rudiment. The cells of the mesophyll of the leaf-base contain abundant starch grains, which become very large in the mature scale leaf. 65

DESCRIPTION OF FIGURES.

Figs.109-134. The Dormant Leaf. (figures unless otherwise stated are of Narcissus poeticus,!. throughout the whole section). Fig.109-111. Shoot from a resting bulb in three different views. Natural size. Figs. 112-124. Structure of the leaf, x 680. Figs 112, 113, 115, 117, 119, 121, 123 are of successive pieces of the abaxial epidermis at the base, and at 5, 10, 13, 15, 20, and 25 mms. respectively from the base of the shoot. Figs 114, 116, 118, 120, 122, 124, are of successive longitudinal sections at 5, 10, 13, 15, 20, and 25 mms. resp ectively from the base of the leaf. Figs 125-127 are of the central mesophyll at 5, 15, and 25 mms. respectively from the base of the leaf, x 155. Figs 128- 129 The inverted bundle, x 680. 128. Inverted bundle with trans­ verse commissure connecting another inverted bundle and a normally orientated one. 129. Undifferentiated inverted bundle at 9 mms. from the base. 130. Media n vascular bundle at 25 mms. from the base. X 680. 131. Transverse section of base of shoot, x 14. 132. Median vascular bundle at 5 mms. from the base, x 680. 134. Median vascular bundle at 10 mms. from the base, x 680.

Figs 135-157. The Half-Grown Leaf. Figs 135-141. X 680. 135. Transverse section at 10 mms. from the base. 136-137. Longitudinal sections at 13 and 15 mms respective­ ly from the base. 138-139. Longitudinal sections at 20 mms. from the ba se for the abaxial and adaxial surfaces respectively. 140. Longitudinal section a t 80 mms from the base. Figs 142-146 are of successive pieces of the central mesophyll at 5, 20, 30, 80, and 160 mms respectively from the base of the leaf. Fig 147. Long­ itudinal section at 160 mms. from the base of the leaf, x 680. Figs. 148-149. Narcissus Elvira. Longitudinal sections at 50 mms. from the base of the leaf, x 680. Figs.150-154. Figs. 150-152 The median vascular bundle at the base, 15, and 80 mms. respectively from the base, x 680. Figs 153-154. Inverted bundles at 10, and 80 mms. respectively from the base.x680. Figs.155-157. Narcissus Elvira. The median vascular bundle fet 5, 10, and 200 mms. from the base of the leaf, x 680.

Figs. 158-164. The Mature Leaf. Figs 158-161. Natural size. 158. Base of outer leaf. 159. Base of second leaf. 160. Base of third leaf. 161. Base of innermost leaf. Figs. 162-164. X 680. 162. Transverse section of leaf at 200 mms. from the base. 163. Longitudinal section at 200 mms. 164. Median vascular bundle at 200 mms. 66

Figs. 166-175. The Scale Leaf. 166. Narcissus Eltira. Shoot with scale leaves prior to the resting stage, 18 mms. in length, x Ej. 176. Scale leaf of N. poeticus from a resting bulb, natural size. Figs 167-170 N. Elvira.. 167. Epidermis from a-daxial surface of rudimentary leaf limb, of scale leaf 18 mms. in length, x 680. 168. Trans­ verse section of mesophyll cells from scale leaf 18 mms. in le n g th . X 680. 169. Similar cells from mature scale when the apex has started to wither, x 680. 170. Mature scale spread out, showing venation, natural size. 171 Narcissus poeticus Mature scale leaf when apex has started to wither, natural size. 172. Narcissus Elvira Vascular bundle from scale leaf 18 mms. long. X 680. Figs. 173-175. Haemanthus albiflos. 173. Young plant, natural size, a and b foliage leaves of current year, c and d inner bulb scales, e and f outer bulb scales, g re­ m ains 0 f old bulb scales. Figs.174-175. Two views of the inner bulb scale. Natural size. NARCISSUS POETICUS THE DORMANT LEAF 67

F ig . 109 F i g . n o . F i g .I I I .

F i g . 112 F i g . 113 F ig .H 4

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OoC>o° cz°%°o3% F i g . 116. F i g .118. F ig .117. F i g .115. 68

O

F i g .119 F i g .120

F i g . 124 69

F i g .128,

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F ig .129. ©

© 71 THE HALF-GROWN LEAF.

f i g . 136

F ig .137

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(jj IM foJIÆ j 0)010 I 6 ~

F ig .138

F ig .140.

F ig .141 72

4% F ig .142 F ig .143

F ig .144. F ig .145.

F ig .146. F ig .147

F ig .149. 73

□

F i g .152 o a

F ig .151, F ig ,154, F ig ,153, NARCISSUS ELVIRA

F i g .155

F i g .157 75 THE MATURE LEAF.

Fig.158. Fig.159. Fig.160. Fig.161.

Q ÜO

F ig .164

F ig .165. 76

— ^ ^ ^ C A 1 E LEatt.

N .E lv ir a . Heamanthus albiflos

F T g\l71.

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i g .l 7 2 . 0

F ig,169 F ig ,170 77

PART III

COMPARATIVE ANATOMÏ OP AMARYLLIDACEOUS LEAVES WITH SPECIAL REFERENCE TO THE' INVERTED BUNDLE SYSTEM.

In the following description of the anatomical structure of Amaryllldaceous leaves the classification given In Engler’s Pf 1 anz enfami lien (1930) has been used. The subdivisions of the family are:- (I) AmaryllIdoIdeae containing 5 5 genera. (II) Agavoldeae containing 7 genera. (Ill') Hypoxldoldeae containing 2 2 gen era. (Iv) GampynematoIdeae containing 2 genera. SECTION I ANATOMY OF THE BIFACIAL LEAF.

All the leaves of the plants belonging to the Amaryllld- oldeae and HypoxldoIdeae are bifacial except those given In Table IX. The Agavoldeae has only Doryanthes with bifacial le a v e s . (l) The AmaryllldoIdeae. The Amaryllldoldeae Is characterised by bulbous plants In which the radical leaves arise from the shortened stem axis, and are mostly distichous. The leaf consists of a completely sheathing leaf-base (except the Innermost leaf bearing the flower In Its axil as In Narcissus, ) and a leaf-llmb of simple outline. In a few cases the base of the leaf-llmb narrows suddenly and becomes petlolar as In Calllphurla Hartweglana, Herb, (fig 186) , Eucharls M astersll. Bak. and Baemanthus Katharlnae, Bak. The margin of the leaf-llmb Is entire but may be dilated as In Biphane clllarls, (L) Herb. The leaves are mostly erect but are prostrate In Brunsvlgla glgantea. Heist, and Baemanthus rotundlfollus, Cawl. The leaf-llmb Is typically bi-facial In structure (dorslventral Goebel 1913 p.293), that Is, the two surfaces differ anatomically, the chief assimilating tissue being concentrated at the upper surface, and a single series of parallel vascular bundles being present. The only two exceptions to this are Narcissus and Zephyr ant he s which w ill be described l a t e r . The palisade Is not well developed as Is characteristic for monocotyledons, consisting of a single adaxlal layer of cells 78 of no great depth as In Haemanthus cocolneus, L. (fig 177 )» Nerine corusea (- Kerin© sam ienels (L) Herb. var. corusca^ and Olivia nobllls, Llndl. (fig.181). Haemanthus rotund If ollug, Gawl. Is exceptional In that there Is a well developed palisade two cells deep as shown In fig 178. In many leaves a palisade layer Is not developed as In Eucharls Mastersll. Bak. The palisade cells are frequently of considerable width, expanded parallel to the long axis of the leaf as well as at right angles to It. This results In a considerable reduction of wall area compared with a palisade of narrow cells. To Increase the area Infoldlngs of the wall have been formed In some cases, similar to those of the mesophyll cells of leaves of Plnus. However all the Infoldlngs are orientated at right angles to the leaf surface which results In what Is termed *arm-pallsade." Meyer ( 1 9 2 3 ) states that this Is of frequent occurrence In mono- cotyledonous leaves; Das troplsche Parenchym p. I7 . In Sprekella formoslsslma. Herb, these Infoldlngs are found main­ ly In the poorly developed adaxlal palisade where they often ext­ end to the centre of the cells (fig 1 8 5 )» but they are also found In some of the ab axial sub-epidermal cells which are elongated parallel to the long axis of the leaf. Where the wall Is bent Inwards to form a fold an air space (fig 185)(a), is formed as the two sides of the fold never touch. Where the mesophyll Is of considerable thickness the chioropy1 1 Is confined to the peripheral portions, that In the median part of the leaf being colourless, consisting of large thln-walled cells with extensive air spaces between them. In Narcissus poetlcus, L. part of this central tissue becomes com­ pressed and distorted, while In Gllvla nobllls. Llndl. the great rigidity of the leaves Is due almost entirely to the plates of thickened cells (fig 181 t .) which occur between the vascular bundles especially towards the margins of the leaf. Along the median line of the leaf these cells remain unthlckened. The thickened cells have deeply pitted walls (fig 181 p.) and large air spaces between them. These plates of thickened cells are not present In Gllvla mlnlata. Regel. In many leaves the thin walled ground tissue between the main veins breaks down and elongated vavltles result which run throughout the length of the leaf only being Interrupted where a transverse commissure connects two main veins. In transverse section the leaf has a glrder- llke appearance with the main veins In the webs as In Brunsvlgla Parker 1. var. alba.( =Amaryllls parkerl = A. Bella dona L.var. blanda Eer-Gawl x Brunsvlgla Josephlnae Ker-Gawl). (fig 180). Other genera with this feature are Ammocharls, Buphane, Nerine, Haemanthus, Vallota, Gyrtanthus, Sternbergla, Sprekella, Hlppeastrum, Hymenocallls, Amaryllis and Leucojum. This feature Is not constant throughout each genus as was found when exam­ ining the elaren species of Nerine given In Table VIII. Of these species all have cavities In the leaves except N. filiforme. The extent of break down of the thln-walled cells to form these cavities also varies In the different species of Nerine. 79

In G-alanthus nivalis L. there are definite areas of thln-walled cells hut these do not tend to break down. Mucilage cells are abundant especially In the chlorophyll containing mesophyll. The Individual cells are of great length running parallel to the length of the leaf (fig 178 c). These mucilage cells sometimes contain raphides. In Nerine corusca elongated spirally thickened cells are present but they have no connection with the vascular bundles (fig 189 & 1 9 0 ). These cells are most numerous In the meso­ phyll bordering the cavities that result from the breakdown of thecentral tissue. The closely wound spiral bands are composed entirely of cellulose, no trace of lignification could be found. E.de Pralne (1913) describes similar structures In the leaves of Sallcomla. Duval-Jouve (1868) considered these spiral cells as an a e r a tin g system w h ile Warming (1901) con sid ered them as water-storing structures. For Sallcomla Halket (1911 ) suggests that they facilitate the passage of water from the absorbing epidermis to the aqueous tissue. In N. corusca the spiral cells are probably primarily water-storing but may also function to prevent the collapse of the adjourning mesophyll Into the cavities of the centre of the leaf. Not all the species of Nerine have spiral cells present as Is shown by the following table.

TABLE: V III.

Spiral cells present Spiral cells absent.

Nerine flexuosa, Herb. Nerine undulata (L) Herb. Nerine sam lensls, (L) Herb. Nerine pudlca, Hook.f. Nerine curvlfolla (Jacq.) Nerine flllfolla, Bak. Herb. Nerine excellens. Moore. Nerine crispa. Hort. Thorburn. (= N.flexuosa x N. humllls var. major.) Nerine tardlflora. Hort. Nerine Bowdenll, W. Watts. Van. Tubergen. (= N.excellens major tardl- f o l l a . )

I Nerine corusca. (=N.samlensls (L) Herb. var. corusca.) 80

The leaf-llmb Is traiaersed by a series of parallel vascular bundles which are connected by transverse commissures. In transverse section the main bundles can be seen to form a single system (figs 180 182 & 18?), and all the bundles are normally orientated. At the apex of the leaf of Gllvla nobllls Llndl. the marginal veins Join on to the more median ones which end blindly In the mesophyll but a main vein may end In the centre of a transverse commissure, or end blindly In the meso- phyir as shown In fig 184* In the leaf-limbs with narrow petlolar bases the parallel vascular bundles are crowded together In the base where they have the appearance of an open arc as seen In transverse section. Passing Into the expanded portion of the leaf-llmb the peripheral bundles curve sharply outwards while the median ones maintain their direct course, see fig 186. The leaves never reach any great thickness so that no part of the mesophyll Is remote from the vascular system. As the vascular bundles are nearer the upper surface than the lower In many cases, the upper surface with the greatest amount of assimilating tissue has a better connection with the vascular system. (II) Agavoldeae. In the Agavoldeae Doryanthes excelsa, Correa. Is the only species that was found to have bi-facial leaves. The leaf of this species resembles the concentric leaf In general structure, but differs In that the small adaxlal bundles are normally orientated. ( I I I ) The Hypoxldo Id ea e. (a) The Alstroemerleae. The Alstroemerleae Is characterised by leafy aerial shoots In contrast to the bulbous plants of the Amaryllldoldeae. The alternate leaves have short petlolar bases which In many species are twisted so that the lower surface becomes the upper surface as Is fr e q u e n tly found In woodland g r a s s e s . Owing to the In­ version of the lamina the palisade Is developed at the morpho­ logically lower surface which has become the physiologically upper surface as In Bomarea caldaslana. Herb. In contrast to this the vascular system remains passive so that the Individual bundles appear to be Inversely orientated, that Is, with the phloem to­ wards the upper surface which Is actually the lower surface as shown In figs 191 and 194- Czapek (1898 p. 429) gives the following explanation of this phenomena for the leaves of Alstroemerla. The leaves assumed a profile position and became radial In structure (similar at both surfaces) as a protection against conditions of Intense Insolation and transpiration. With the change^again In the conditions a further twist took place through 90 and the leaf came to have an Inverted dorslventral s tr u c tu r e . 81

The epidermis Is thln-walled, acting as a water storage tissue, as the Individual cells are often very large. The stomata are small, slightly sunk and without subsidiary cells (fig 192). The mesophyll Is generally spongy In type but a rather Indefinite palisade may be formed (fig 193). Large mucilage cells are of frequent occurrence. A single system of parallel vascular bundles traverse.the leaf. Thus the leaves of this group are bl-faclal as In the Amaryllldoldeae. (b) The H ypoxldeae. A considerable amount of work has been done on this group by Baker (1888), Scharf (1893), Schulze (1893), Nel (1914). The radical leaves arise from a rhizome or a shortened stem axis (frequently a corm), and are linear, entire, plicate or folded about the mld-rlb. The leaves are all bl-faclal except for some species of the genus lanthe which will be described later. A constant feature throughout the group Is the presence of four subsidiary cells In connection with each stoma (fig 196) as described by Scharf. The large thln-walled epidermis may act as a water storage tissue as In Gurcullgo Sumatrana, Roxb. described by Scharf, and Hypoxls vlllosa, Llnn.f. (fig 201 & 202) Mollnerla recurvata,(Dryand) Nel. has a plicate leaf with a petlolar base resembling the palms. The rigidity of the leaf Is due almost entirely to long hypodermal sclerotic cells as In figs 197 and 199,s. The mesophyll Is compact but a palisade of comparatively short cells may be present (fig 199). A typical type of hair Is present which has a multlcellular base and Is crowned by large thln-walled cells, only one of which Is shown In fig 198. Nel (1914) criticises the developmental stages described by Scharf (1893) and describes the stages he found. There Is a single series of parallel vascular bundles of which the larger ones are located In the ribs (fig 195). In the genus Hypoxls,worked out In detail by Nel,the leaves are lanceolate, folded about the mld-rlb and typically bl-faclal In structure. The chief variations found are In the number and arrangement of the strong veins which Nel Illustrates In his paper, fig 2. page 269. The long silky hairs of Hypoxls vlllosa, Llnn.f. (fig 201) are similar In structure to those of Mollnerla recurvata (Dryand) Nel, but the terminal hair cells are thlck-walled and lie parallel to the surface of the leaf. (c) Gonanthereae. For this group only herbarium material could be obtained for Gyanella gapensls, L. which has small bl-faclal leaves (fig 203J. An examination of the literature of this group suggests that the leaves of all the species are bl-faclal. 82 (d) Gonostylideae. The plants of this group are characterised by linear or equitant leaves. Schmidt (1893) cites four genera as having equitant leaves which are concentric in type and said to re­ semble those of Iris. For this group only herbarium material could be obtained of the bi-facial linear leaves of Lanaria plumosa, (L) Alt. As Scharf gives a good description of this species only brief reference will be made to It here. The epidermis consists of a mixture of sclerotic and thln-walled cells. The mesophyll Is compact and no palisade Is organised ( f i g 2 0 4 ). Large thln-walled cells, lacking chlorophyll, occur between the main veins. In each half of the lamina there are five large vascular bundles with consplclous sclerenchymatous sheaths. The median bundle , and two marginal ones are smaller Between these large bundles are numerous small ones, the greater number being towards the abaxlal surface. These small bundles are all normally orientated (fig 205).

SEGTION 2 . GONGENTRIG LEAVES. The object of this general survey of the anatomy of Amaryllldaceous leaves was to ascertain how frequently the con­ centric type of structure occurs. Of the 34 genera examined only six contain species with concentric leaves besides the Conostylldeae, see Table IX.

T ABLE IX. !"■ - . - - - 1. Zephyranthes ( - Amaryllis)x Amaryllldoldeae 11. N arcissu s

la n th e . Hypoxldoldeae Gonostylls% Iv . Conostylldeae. B lan coa^ . # Anagozanthus^ Phlebocarya^

V. Agave.X Agavoldeae vl. Beschornla. v l l Fourcroya.

Those genera cited by Arber (1918) are marked w ith an a s t e r is k . m 83 The Conostylldeae were examined by Schmidt (1893), and Arber confirms his work on Anagozanthus. Unfortunately no material of any of these genera could be obtained. However It seems certain that In the genera cited by Schmidt the leaves are concentric. The proportion of species with concentric leaves In any given genus varies. Thus In Narcissus all the species except two have concentric leaves, Arber (1921), while In lanthe only two species were found with truely concentric leaves. The concentric leaf (Including the radial leaf of Goebel ( 1 9 1 3 ) p . 2 9 3 ) has the assimilating tissue similarly developed all round the leaf (that Is at the upper and lower surfaces when the leaf Is flattened.) The vascular system Instead of having a linear arrangement as seen In transverse section (bl-faclal leaves) Is circular or elliptical as In stems. This means that a certain number of the bundles must show Inverted orientation, that Is, with phloem orientated towards the upper surface. Goebel (1913) Introduced the term "Unlfaclal" for those leaves where the concentric structure Is obtained by the loss of the upper surface and the resultant fusing of the edges of the lower surface as In Iris, Juncus and lanthe. More frequently however the concentric structure Is obtained without the loss of the upper surface as In Zephyranthes, Narcissus, Beschornla, Agave, and Fourcroya. lANTHE. The genus lanthe w ill be described first as some species produce a series of leaves on the Individual plant, the outer ones being bl-faclal while the Inner ones pass through transitional forms to a concentric type. The leaves are all radial, few In number (two to seven) and arise from a corm which Is clothed with a tunic of fibres. lanthe stellata (Linn f11.) Williams var. Gawlerl Bak. lanthe ovata (Linn fll.) Sallsh. lanthe flacclda Nel. lanthe curcullgoldes (Bol) Williams.

These species have linear bl-faclal leaves, frequently folded about the mld-rlb. The mesophyll Is compact In lanthe flacclda and spongy with large air spaces In lanthe stellata var. Gawlerl. Mucilage cells are of frequent occurrence and In addition to these there are mucilage ducts In connection with the vascular bundles, each bundle having a single large duct at the protoxylem end. The duct Is lined with a small-celled epithelium similar to that of the resin ducts characteristic of 84 some Gymnosperms. (Scharr 1893). A single series of normally orientated vascular bundles run throughout the length of the leaf, the bundles having a linear arrangement as seen In trans­ verse section. In lanthe ovata the apices of the leaves occasionally end In cylindrical points, and here there Is an approach to the concentric leaf type, (unlfaclal). The adaxlal surface becomes reduced and at the same time the vascular bundles appear In a deep IT as seen In transverse section. lanthe curcullgoIdes has narrow linear leaves which are triangular In transverse section. Three vascular bundles are present, arranged In an arc open to the adaxlal surface.

lanthe minuta, (Llnn.f.) Williams, lanthe Schlechterl, (Bbl.) Williams.

- In these species there Is a strong tendency to produce a concentric leaf, the leaf-llmb becoming reduced to a solid tapering rod. lanthe minuta. In this species the leaves on an Individual plant form a series, the outer ones being relatively broad, membraneous and bl-faclal In structure, while the Inner ones are cylindrical, somewhat fleshy, and approach the concentric type In structure (figs 225 to 228). The adaxlal surface of the Inner leaves Is much reduced but never becomes eliminated In this species.(figs-231 to 235). These leaves have a well developed palisade, two to three cells deep, but It never becomes complete­ ly concentric as beneath the adaxlal epidermis colourless parenchyma cells form a strip extending the whole length of the leaf-llmb. In the second leaf of the series, which Is transit­ ional In form, the palisade extends all round the leaf, as seen In transverse section except for a small portion of the centre of the adaxlal surface (fig 2 3 0 ). At the apex of this leaf the adaxlal surface becomes reduced and at the same time the extent of adaxlal palisade tissue (fig 231). In the third leaf the adaxlal surface Is greatly reduced at the base of the leaf-llmb ( f i g 2 3 2 ) and no palisade Is present In relation to this surface. At the apex of the third leaf the position of the adaxlal sur­ face Is Indicated by two or three colourless cells (fig 234). Similar distribution of the assimilating tissue was described by Adamson (1925) p.608-9 for the leaves of Juncus squarrosus. The vascular bundles have a linear arrangement In the membraneous outer leaf as seen In transverse section, (fig 229). In the second leaf they form an open arc, while In the third and fourth leaves they are arranged In a deep U open to the adaxlal surface (figs 231 to 235). Thus although the Inner leaves approach the concentric type, a truely concentric leaf Is not developed. 85 lanthe Schlecherl. All the leaves produced on the individual plant are similar In this species, being of a transitional type resembling the Inner leaves of lanthe minuta. Each leaf con­ sists of a completely sheathing, membraneous leaf-base which encloses the bases of the Inner leaves and a solid cylindrical leaf-llmb, flattened along the adaxlal surface, and tapering at the apex, (fig 264) The mesophyll of the leaf-base lacks chloroï^iyll, and the smallest cells are found towards the abaxlal surface. At the base of the leaf-llmb a palisade be­ g in s to form at the abaxlal surface (fig 259) but soon becomes concentric. Throu^out the leaf-llmb there Is a well developed palisade, three to four cells deep and equally developed on all sides. The mesophyll In the centre of the leaf contains very little chlorophyll and consists of thln-walled cells with large air spaces between them (figs 261 to 2 6 5 ). At the lower end of the sheathing leaf-base the vascular bundles are numerous, but after running parallel for a short distance they fuse In groups of three or four so that the upper part of the sheath Is traversed by a relatively small number of bundles (fig 2 6 4 ). In transverse section the bundles are found to have a linear arrangement (fig 258). Passing Into the base of the leaf-llmb the bundles become arranged In an arc ( f i g 2 6 0 ) which gradually deepens to a ü open to the adaxlal surface, and this condition Is preserved throughout the leaf- llmb, even in the narrowed apical portion, (fig 2 6 3 ) At the apex of the leaf where the bundles are few In number and re­ latively close together two or more of the mucilage ducts In connection with the protoxylems may fuse. lanthe alba (Linn fll.) Sallsb. In lanthe alba a series of leaves are produced on each plant similar to that of lanthe minuta, but with the Important difference that the Inner leaves are truely concentric (figs 236 to 2 4 4 ). Transitional leaves are of frequent occurrence where the lower portions are broad and membraneous while the upper portions consist of long, tapering, solid points (fig 237). In these solid apices there Is an approach to unlfaclal structure, see p . 9 2 . The cylindrical Inner leaves have a well developed con­ centric palisade while the central tissue consists of thln- walled spongy tissue with scanty chlorophyll (fig 257). In transverse section the vascular bundles are arranged In a circle at the periphery of the spongy tissue (figs 253 & 254). Several large bundles are present with smaller ones between them but lying somewhat nearer the assimilating tissue. When the vascu­ lar bundles become concentrically arranged at the base of the 86 leaf-llmb the adaxlal surface is not affected and so is present in all the leaves although it is reduced in the con­ centric ones. Thus the bundles lying directly beneath the adaxlal surface have Inverted orientation,that Is, with the phloem uppermost (figs 253 & 254)• The origin of these bundles w ill be traced later. lanthe aquatlca, (Linn fll.) Williams. In this species the leaves are all of one kind and resemble those of lanthe Schlechterl In appearance (fig 265 & 2 6 4 ) but differ In two Important respects In structure:

( I ) The vascular bundles become concentrically arranged at the base of the leaf-llmb.

( II ) The adaxlal surface becomes eliminated at the same tim e. Thus the leaf Is unlfaclal In structure In contrast to lanthe alba. A well developed concentric pallsdde Is present Xflg 265). Just within the peripheral assimilating tissue are the vascular bundles which have a similar arrangement to those of lanthe alba. The central ground tissue of the leaf Is com­ posed of a network of colourless cells owing to the development of large air spaces (fig 269). This Is a characteristic feature of water plants. (Arber,"#Ater Plants.")- 1920. An examination of several species of the genus lanthe suggests that the bi-faclal leaf Is primitive and that the con­ centric leaf Is the secondary or derived form. This would make lanthe aquatlca the most advanced species. The tendency is to­ wards the formation of a unlfaclal leaf as In the genus Juncus. Comparing the two genera many sim ilar forms can be found so that considerable parallel development must have taken place.

NARCISSES. The genus Narcissus Is characterised by linear concentric leaves having the adaxlal surface present. The leaves vary considerably in form, being cylindrical with flattened adaxlal face as In N. Jonquil 11a var. jonqullloldes, Wlllk. (fig 208) or flattened with a definite mld-rlb area as In N. poetlcus. L., N. tazetta, L., (Arber 1921) and N. trlandus, L.. (fig 209). The concentric palisade Is a single cell deep, the Individual cells being greatly elongated at right angles to the surface. Beneath the palisade are rounded cells with considerable chlorophyll content. Only these peripheral tissues contain chlorophyll, the vascular bundles being Imbedded In an extensive colourless, thln-walled tissue which may become compressed and broken down locally, as In fig 209. The arrangement of the vascular bundles l3 typical for the genua. The largest bundles occur across the 87 centre of the transverse section while near the abaxlal surface. Just outside the assimilating tissue, are numerous small bundles. Both the large and the small bundles are normally orientated. Beneath the adaxlal surface Is a series of small bundles showing Inverted orientation (figs 209 & 208) This is true for all the species except the two nearly allied forms, N.bulbocodlum, L., and N.monophyllus. T.Moore. (Arber 1921) In these leaves the two sets of normally orientated bundles are present but the Inverted bundles are absent (fig 210).

ZEPHYRANTHES.

Zephyr anthes Atamasco, Herb, produces several linear. concentricir lc lleaves. e A well developed palisade, a single cell deep. Is present as seen In transverse section (fig 2 0 7 ) . The central mesophyll lacks chlorophyll and forms a water storage tissue. A single series of large normally orientated vascular bundles are present and about eight small Inverted bundles as shown In the transverse section, (fig 206). There are no small abaxlal bundles unlike Narcissus. Z. tublspatha, (Ker.) Herb., Z.verecuna, Herb., Z.carinata, (Spreng.) Herb., and Z. Candida, Herb (Inner leaf, fig 286) resemble Z.Atamasco, Herb. In structure. ~Z. rosea (Spreng.T Llndl. has very narrow leaves which have no adaxlal bundles and so resemble N. bulbocodlum. In the two genera. Narcissus and Zephyranthes, the con­ centric structure Is correlated with a tendency for the leaves to become distinctly fleshy as Is also shown to a lesser degree In the genus lanthe. (11) AgavoIdeae. The leaves of the five genera of the Agavoldeae examined all had an adaxlal Inverted bundle system except Doryanthes excelsa, Correa. In this species the small adaxlal bundles are normally orientated. Apart from this exception the leaves of the Agavoldeae are of the usual concentric type. The leaves are linear or lanceolate and are arranged In a rosette on a shortened stem axis. A characteristic feature of this group Is the fleshy nature of the leaves which are often slow growing and reach a great size as In Agave americana, L. Correlated with the thickness of the leaf Is a great Increase In the amount of vascular tissue compared with thin leaves of equivalent surface areas. This Increase usually takes the form of stratification of the parallel vascular bundles as seen In transverse section, several lines of vascular bundles are found In the ground-tissue between the upper and lower epidermis. These bundles can readily be divided Into two distinct systems: 88

Ci) The dominate system consists of normally orientated bundles and occupies the lower three-quarters of the transverse section. (11) Beneath the upper epidermis Is a small area occupied by the second system. This consists of small Inverted bundles, except In Doryanthes excelsa, Correa., where they are normally orientated. The separation between the two systems Is sharp even In Doryanthes excelsa. Correa, as the largest abaxlal bundles come next to the small adaxlal ones. The peripheral mesophyll Is similarly organised at both surfaces, that Is, where a definite palisade Is formed It Is concentric. The vascular bundles are Imbedded In a thln-walled, water-storage tissue with large air spaces between the cells, and completely lacking In chlorophyll content.

Agave amerIcana L. Agave dlsceptata, Drummond.

, , The.leaves,of.Agave amerIcana have sheathing leaf-bases, and broad fleshy leaf-îlmba "tâperlhg at the aplcesT Stout teeth occur at Intervals along the margin. The leaves of Agave dlsceptata are small and linear with ciliated margins. This species belongs to the small section Plllferae of the genus Agave, characterised by the leaf edge splitting Into distinct threads.(Baker 1888). The two species are similar In structure. The epidermal cells have very thick cuticle, and the stomata are sunk deeply below the level of the epidermal cells. The mesophyll Is compact, and the peripheral layers are organised as a palisade about four cells deep (fig 213). Certain of the marginal bundles become surrounded by 8 cl ere nchymat ous cells and become cut off from the rest of the leaf by the formation of cork. The portion of the leaf margin thus cut off dries, and splits away, forming a white marginal thread (figs 211 & 212). Wlesner and Baer (1914) describe other species having similar marginal threads. The normally orientated vascular bundles occupy the greater part of the section (fig 211). Across the centre of the transverse section but somewhat nearer the adaxlal surface Is a line of large vascular bundles with extensive fibrous sheaths. The fibrous sheaths In connection with the phloem Is more extensive than those In connection with the xylem. The marginal bundles have phloem fibres only. 89

Towards the lower epidermis the vascular bundles become progressively smaller. They have fibrous sheaths In connection with the phloem, that Is, on the abaxlal side of each bundle. In the adaxlal portion of the transverse section there Is a much weaker system of Inverted bundles. These small bundles have phloem fibrous sheaths, thus the fibres are on the adaxlal side of each bundle. In some cases simple strands of fibres are present not In connection with the vascular bundles. Some of the bundles are not completely Inverted but are placed obliquely or parallel to the epidermis^ the xylem pointing either right or l e f t . Beschornla Juccoldes, Hook. The leaves of Beschornla Juccoldes, Hook, are lanceolate frequently ending In solid points and differ from those of Agave In that only the petlolar bases and median portions of the leaf-limbs are thickened. The mesophyll Is compact, and a con­ centric palisade Is present which Is two cells deep (fig 220^. The thin portions of the leaf, that Is, the lamina and petlolar wings, have a single series of vascular bundles (figs 217& 2 1 8 ). These bundles are all normally orientated and consist of strong bundles with small ones between them. At the base of the leaf the vascular bundles are organised In a similar way to those of Agave amerlcana (compare Agave dlsceptata fig 211 & Beschornla Juccoldes fig 219). Beneath the adaxlal surface Is an Inde­ finite line of small Inverted bundles. The rest of the section Is occupied by normally orientated bundles which become smaller towards the abaxlal surface. The smallest bundles are In close approximation to the abaxlal surface and are numerous. In some cases strands of fibres only are present. The bundles have small sheaths In connection with the phloem while the large bundles have small xylem and phloem sheaths. Passing from the petlolar base Into the thickened median portion of the leaf- llmb the number of vascular bundles becomes reduced. In the centre of the leaf there are three lines of vascular bundles present In the thickened median portion. The central llnè, contlnous with that of the lamlna-wlngs, consists of large normally orientated bundles. Towards the abaxlal surface there Is a line of smaller, normally orientated bundles, while beneath the adaxlal surface are four small Inverted bundles (fig 218). Towards the apex of the leaf the peripheral bundles die out and only the median line Is left (fig 217). The apex of the leaf frequently ends In a solid point where the vascular bundles be­ come arranged In a horse-shoe form and the adaxlal surface tends to disappear (figs 216 215 & 214). Small bundles however always Indicate the position of the adaxlal surface after It has dis­ appeared (fig 214). 90

Fourcroya oubensls, Haw, var. inermis. Baker. Fouroroya cubensis, Haw. var. Lindenli. Jacobi.

The leaves of Fourcroya resemble those of Beschornla Juccoldes In structure. In the petlolar base there Is an ex­ tensive series of vascular bundles. The small Inverted bundles are numerous although the leaf examined was a young one. (fig 224) Certain of these bundles belonging to the Inverted system were obliquely placed or were orientated parallel to the epidermis. Both series of peripheral bundles disappear In the lamina wings. In the thickened mld-rlb region they also die out towards the leaf apex leaving the single series of strong bundles. Doryanthes excelsa, Correa. In Doryanthes excelsa the mesophyll Is compact and a palisade layer Is orgalnsed (fig 223). The leaf has a similar structure to those of Fourcroya oubensls and Beschornla Juccoldes but the adaxlal bundles present In the thickened portions of the leaf are all normally orientated. Extensive sheaths of phloem fibres are present In connection with all the bundles except the adaxlal ones while the corresponding xylem sheaths are much smaller. The adaxlal bundles have large sheaths of xylem fibres which are orientated towards the adaxlal epidermis and very small sheaths of phloem fibres (fig 221). In the Agavoldeae the leaves are concentric with a system of adaxlal Inverted bundles which may die out before the apex of the leaf Is reached. The leaf-limbs of Beschornla Juccoldes, Fourcroya oubensls, and Doryanthes excelsa frequently end In long solid points. In these points the normally orientated bundles only are present. When they become concentrically arranged, some of them become Inverted, but these Inverted bundles are distinct from those of the Inverted bundle system present In the lower part of the leaf. From the structure of these solid apices Arber (1922) Infers that, as for Tullpa, the leaf-llmb Is equivalent to the leaf-base only of dicotyledonous leaves, the solid apex representing the vestigial petiole, the arrange­ ment of the bundles In a circle determining Its petlolar structure. But according to the phyllode theory the presence of Inverted bundles In the lower part of the leaf would Indicate that the entire leaf was petlolar, and not a leaf-base structure. Thus the structure of these leaves allows of the application of both parts of the phyllode theofy which means that the leaf Is morphologically: (a) a leaf-base, and (B ) a petiole, which of course Is Impossible. 91

SEGTION 3 . THE ORIGIN AND SIGNIFICANCE OF THE INVERTED BUNDLE SYSTEM.

Work on the Inverted bundles has been up to the present confined to descriptions of the arrangement and structure found in th e mature le a f-lim b s except Adamson ( I 9 2 5 ) for the genus Juncus, and lonay (1902) for Omithogalum. They describe the changes that take place from the bl-faclal to the unlfaclal parts of the leaf. When the course of the Inverted bundles Is followed down Into the leaf base It Is found that they do not always join on directly to the stem vascular system as do those bundles show­ ing normal orientation. In the upper part of the leaf-base the Inverted bundles either become diverted to the system of normally orientated bundles or end blindly, the bundles dying out In the ground tissue. From the examination of various genera three distinct types of Inverted bundle systems were found:

( 1 ) The la n th e ty p e. The simplest type Is that found In the genus lanthe. (also Juncus (Adamson) and Ornlthogalum (Lonay) ). Here certain bundles showing normal orientation In the bl-faclal part of the leaf curve round and enter the concentric part as In­ verted bundles. In lanthe this tàkes place In the transition region from the bl-faclal sheathing leaf-base to the unlfaclal leaf-llmb.

( II ) The Agave type. In Agave amerlcana special branches given off from the normally orientated bundles become the Inverted bundles. These branches move towards the adaxlal surface, curve sharply and take a vertically upward course becoming Inverted In the p r o c e ss. (III) The Narcissus type. In Narcissus the Inverted bundles pass down from the leaf-llmb Into the upper part of the leaf-base where they die out In groups of storage trachelds. The Inverted bundles are connected Indirectly with the normal ones by numerous trans­ verse commissures. In Zephyranthes a combination of two of these types forms the Inverted bundle system. The four or five median bundles 92 resemble Narcissus, each bundle ending In groups of storage trachelds. The two marginal Inverted bundles are derived from the normally orientated ones as In lanthe. (a ) THE ORIGIN OF THE INVERTED BUNDLES IN THE GENUS lANTHE. lanthe alba (Linn f .) Sallsb.

A general description of this plant has already been given, page 85- The change from bl-faclal to concentric can be traced In two different parts, In these leaves: (l) In the trans­ itional leaves where the membraneous portion passes over to the solid apex and (11) at the base of the cylindrical Inner leaves.

In the transitional leaves the change from membraneous to solid Is accompanied by a change In shape of the section. The adaxlal surface becomes deeply grooved (fig 246) and gradual­ ly dies out higher up so that the edges of the abaxlal surface j o i n . ( f i g 2 5 2 ). The adaxlal surface appears as a small notch In the section just before It disappears (fig 249). At the sa time the arrangement of the vascular bundles changes gradually from a broad arc to a deep U. Finally this U , which Is open to the adaxlal surface closes, and the vascular bundles become arranged In a circle as seen In transverse section (figs 246 to 2 5 2 ).

In the cylindrical Inner leaves all the bundles present In the membraneous bl-faclal, sheathing leaf-base pass Into the solid leaf-llm b, the marginal ones curving strongly and taking an oblique course, so that they come to lie beneath the adaxlal surface as shown In the series of sections, 256 to 253. These bundles become Inverted, and the adaxlal surface never disappears unlike the transitional leaves. lanthe aquatlca (Linn f.) Williams. The change from bl-faclal to concentric Is located In the transition region between the sheathing leaf-base and the leaf- llmb. The peripheral bundles of the sheath curve round and become adaxlal. Inverted bundles In the leaf-llmb as In lanthe alba, but accompanying this Is the loss of the adaxlal surface ( f i g s 2 6 6 to 2 6 8 ). Thus the leaf-llmb Is unlfaclal In lanthe aquatlca arid resembles the axes of Juncus effusus In this respect as described by Adamson (1925). In Ornlthogalum caudatum, Alt. described by Lonay (1902), two types of leaves are present as described for lanthe alM . In the embryonic leaf Lonay finds three distinct parts: (ij a bl-faclal leaf-llmb which Is termin­ ated by a unlfaclal apex, (ll) and a sheathing leaf-base, (111). In the mature leaf all these parts are not present, the leaf-base passing directly to the unlfaclal leaf-llmb. The vascular bundles become concentrically arranged so that In the mature 93 form the leaf resembles that of lanthe aquatlca. (b) THE ORIOIM OF THE INVERTED BUNDLES IN AGAVE AMERIGAM.L.

Several young offshoots from a plant growing at Kew were examined. The leaf Is formed by an extensive merlstematlc zone, ( f i g 2 7 0 f ) just outside the complicated stele of the stem axis. This cylindrical merlstem forms the ground tissue of the leaf on the outside. The abaxlal tissues are formed first and develop­ ment proceeds until the adaxlal epidermis Is formed and the leaf becomes free from the stem at that level. The margins of the leaf become completed first, and for a considerable distance the leaf has a median attachment only to the stem as shown In the outer leaf, fig 270, a. The vascular bundles pass out obliquely from the stem Into the base of the leaf Interrupting the merlstematlc tissue. The bundles pass out In séries. At the base of the merlstematlc zone, where only a little abaxlal leaf tissue has been formed, a series of small bundles pass out as shown In the Inner leaf, fig 2 7 0 ,b. These bundles have large sheaths of fibres In connect­ ion with the phloem. Higher up a rather Indefinite series of larger bundles pass out and they occupy a position mid-way be­ tween the lower and upper epidermis. Finally the main series of large bundles pass out just before the leaf becomes detached. Those at the margin pass out first and there Is a gradual pro­ gress towards the centre. These bundles are all normally orientated but In the median portion of some leaves when the last of the vascular bundles are passing out, there were two small bundles present, one of which showed Inverted orientation, (fig 2 7 0 c) and the other partially Inverted orientation (fig 270 dT, the xylem being at about 45^ to the vertical as seen In trans­ verse section, fig 2 7 1 , 1. For a considerable distance (about 1 cm) after the leaf has become free from the stem, no Inverted bundles are found In the leaf-base (except for the two axial Inverted bundles In some of the leaves.) In this part of the leaf-base the large normally orientated bundles, which passed out last Into the leaf, gradually recede from the adaxlal epidermis and then proceed to give off the Inverted bundles. These are formed by traces which curve out towards the adaxlal epidermis and In doing so become Inverted. These traces then turn vertically upwards and run throughout the leaf-llm b, dividing up Into several separate bundles which become arranged In several planes, parallel to the surface. In older leaves. This Is brought about by certain branches curving towards the centre of the leaf and others to­ wards the adaxlal surface so that In transverse section more than one line of vascular bundles Is found. In fig 271 there are two median axial Inverted bundles present and a third Inverted bundle Is about to be given off by one of the large bundles. A portion of the phloem has moved round at right angles to that of the large bundle while the xylem Is separating Into two groups.(fi|.2 7 2 ). 94 The small bundle so formed sweeps round towards the adaxlal sur­ f a c e ( f i g 2 7 3 ) and becomes Inverted (fig 274). The other large bundles give of Inverted bundles In the same way. The order of the appearance of these bundles In the leaf examined Is shown In f i g 2 7 5 , at which level the median axial bundle has divided.

Thus In many leaves of Agave amerlcana the Inverted bundles have only an Indirect connection with the stem system while In other leaves only two of the many Inverted bundles have direct connection. In the latter case the only difference appears to be that the two Inverted bundles In question are given off much earlier than the others, that Is, before the leaf has entirely separated from the stem.

(o ), THE ORIGIN OF THE - INVERTED BUNDLES IN NARCISSUS POSTICUS.L .

As already mentioned In connection with the growth of the leaf. Narcissus poetlcus has a system of Inverted bundles which die out In the upper part of the leaf-base. This system is complicated and difficult to trace owing to the occurrence of numerous transverse commissures connecting the individual bundles among themselves and with the normally orientated systwn.

The bases of two leaves of a nearly mature shoot were ex­ amined. A circle of normally orientated bundles, as seen in transverse section, pass Into the leaf-base. Those passing Into the leaf-base proper run straight through the leaf to Its apex, while those passing Into the sheathing portion die out In the crescent shaped ridge of tissue at Its apex. Thus there is no curving of the bundles of the sheath into the base of the leaf- llmb as In lanthe aquatlca.

In sectioning the shoot adaxlal bundles first appear in the inner leaf about six mms. from its junction with the stem. At this level the sheath is complete and all the normally orien­ tated bundles are present in the sheathing portion. As the base of the leaf is not mature (growing shoot) the adaxlal bundles consist of strands of procamblum In the leaf-base (fig 277)» these strands appear to have been formed by the late division of parenchyma cells, sim ilar to the peripheral bundles In the leaf- base of Omithogalum caudatum, A lt. described by Lonay (I9 0 2 ). The original procambial strands divide, and at a higher level differentiation takes place. The median bundle has numerous small llgnlfled storage trachelds (fig 278) which become reduced at a hi^er level to one or two trachelds, as seen In transverse section. The procambial strand on the right of the median one is pecular In that the lignlfied trachelds first appear some distance from It, being separated by three or four large paren­ chyma cells( fig 2 7 9 ). The tracheal group moves towards and finally joins the procambial strand. Adaxlal bundles appear at a higher level In the outer leaf as it is more developed. 95 The first bundle to appear Is a marginal one which ends In a single long tracheld (fig 281). This is followed by a group of about ten small storage trachelds, at which level a transverse commissure passes down from one of the normally orientated bundles (fig 280 )> Above this junction the tracheal mass divides Into two and undifferentiated phloem cells appear on the adaxlal side of each xylem group, which determines the Invented orientation. One of the two bundles now divides again so that three are present. Near the othef margin of the leaf another Inverted bundle appears but It Is Impossible to show that It Is Independent before the transverse commissure joins It. This bundle also divides Into three as described above. Other Invert ed bundles appear In rapid succession most of them having trans­ verse commissures (from normally orientated bundles) which pass down obliquely and join on to their bases.

An examination of mature shoots confirms the independent origin of the inverted bundles, which end blindly in the general mesophyll of the upper part of the leaf-base, in groups of storage tracheids. From these groups single tracheids frequent­ ly pass further down and end blindly in the mesophyll.

(d) THE ORIGIN OF THE IN^RTED BUNDLES IN ZEPHYRANTHES QANDIDA.

A bulb of Zephyranthes Candida, Herb, produces three leaves each year. The outer two have completely sheathing, flask-shaped bases which are fleshy owing to storage starch in the mesophyll. (fig 282). The innermost leaf bears in Its axil the flower of the current season, and has only a partially sheathing leaf-base . (f ig 284) # This leaf is usually much smaller than the other two, even when fully mature. The two out­ er leaves have typically concentric leaf-1im bs.(see page 8?). The innermost leaf has a concentric palisade, but the greater part of the leaf-limb has no inverted bundles.

A single series of normally orientated bundles passes from the stem into the leaf-base. Those passing into the thin sheathing portion die out in the upper part of the sheath, while those passing into the leaf-base proper continue into the leaf- llmb. No inverted bundles are present in the greater part of the leaf-base. The inverted bundles first appear in the trans­ ition zone passing from the leaf-base to the leaf-limb. The two marginal inverted bundles are derived from the normally orientated ones by incurving of the bundles of the sheathing portion of the leaf-base as in lanthe. The four to six median inverted bundles end blindly in groups of storage tracheids in the transition region and do not connect directly with the normal sy ste m .

A mature shoot was examined, which had three foliage leaves To trace the origin of the inverted bundles a shoot was sectioned 96 at three different levels: (i) The highest level on the shoot was the transition region of the outer leaf, i.e. the upper part of the leaf-base, and the lower part of the leaf-limb. (ii) The next was the similar transition region of the second leaf , which was at a lower level, (iii) The last was the base of the shoot to the level of the mature leaf-limb of the third leaf.

A section taken in the centre of the sheathing leaf-base shows a circle of normally orientated vascular bundles of which nine large bundles are present in the leaf-base proper and four or five small ones in the thin sheathing portion (fig 285) • It is only in the upper part of the leaf-base that the inverted bundles begin to appear. In the outer leaf of the shoot examin­ ed, the first inverted bundle appears in the median part of the adaxial surface of the leaf-base proper (fig 285). This is followed by an inverted bundle on the left of the median one (fig 286) and then one on the right (fig 289). The fourth appears on the right of the third (fig 293). These inverted bundles are all similar in structure. At the extreme base there are one to three tracheids (fig 290), without any phloem present. These tracheids are short and frequently elongated at right angles to the long axis of the bundle (fig 294). The xylem increases rapidly in amount until six to ten tracheids are present in the thickest part of the storage base (figs 287, 291, & 295). The phloem now begins to organise on the adaxial side of the xylem and so determines the inverted orientation of the bundles. At higher levels the bundles decrease rapidly in size. The phloem becomes organised as a group of small cells and the xylem becomes reduced to one to four tracheids (figs 288, 292, & 296). This is the general form of the inverted bundle throughout the leaf- limb. By dehydrating material in alcohol and clearing in xylol it becomes sufficiently transparent for the inverted bundles to be seen in the solid and the details of their bases drawn. Figs 320 and 321 are of the ends of two bundles, drawn from material treated in this way. When the thin sheathing portion of the leaf dies out all the bundles except two die out with it. Fig 298 is of the end of one of the bundles just before it dis­ appears . The two peripheral bundles of the sheath become divert ed, curving into the base of the leaf-limb (figs 300& 3 0 1 ). The sheath usually dies out more quickly on one side than the other and one peripheral bundle is also in'advance of the other. During this curvature the two peripheral bundles become inverted (fig 302). They are thus exactly similar to the inverted bundles, found in lanthe alba and lanthe aquatica. In some leaves a variation was found in that the two marginal inverted bundles are formed by two branches given off by the two marginal normally orientated bundles of the leaf-base proper. In either mode of origin the peripheral inverted bundles are derived from the system of normally orientated bundles, in contrast to the rest of the inverted bundles.

The second leaf of the shoot examined differed from the 97 outer in two ways: (i) the two marginal inverted bundles appear first, and (ii) all the rest of the inverted bundles appear in the base of the leaf-lim b. These variations are simply due to the different level at which the sheath dies out. The two marginal inverted bundles are represented by strands of pro- cambium (fig 3 1 1 ) which only become differentiated in the centre of the leaf-lim b. The order of the appearance of the five median inverted bundles is shown in figs 3 0 6 3 0 7 3 0 8 3 0 9 & 3 1 0 . The arrangement is not identical with that found in the outer leaf, also an extra bundle is present here. These bundles consist of strands of procambium at the base (fig 3 I 3 ) . Above this, groups of storage tracheids are found, and finally the bundles become greatly reduced in size, usually a single tracheid being present (fig 312). At the level of fig 286 the inner leaf is cut in the centre of the leaf-limb. Here all the bundles are differentiated into xÿlem and phloem. There are nine normally orientated bundles as in the outer leaf, and seven small inverted bundles the whole forming a concentric system.

In the non-sheathing base of the third leaf, seven vascular bundles are present, all of which have lignified xylem ( f i g 3 1 4 ). At a higher level four adaxial procambial strands appear which represent four inverted bundles. These strands end blindly in the general mesophyll at the base of the leaf, so resembling the median inverted bundles of the sheathing leaves. At the level of fig 3 1 5 the four adaxial strands and the two marginal bundles of the normally orientated system consist of undifferentiated procambial strands. The rest of the normally orientated bundles have only two or three proto­ xylem elements lignified. The metaxylem is undignified and resembles that found in the growing region at the base of the Narcissus leaf (fig 324). Proceeding higher up in the leaf the adaxial bundles die out, and the normally orientated bundles become fully differentiated (figs 316 to 319). At the level of f i g 3 I 8 all the bundles are differentiated including the two inverted ones. A concentric palisade is present at this level. In the upper half of the leaf-limb no inverted bundles are present as shown in fig 319. A summary of the results described above isshown in f i g 3 2 2 which was drawn from material cleared in xylol as already explained. The inverted bundles are shown in heavy black continous lines, and the normally orientated ones in broken lines. This is typical for all the leaves except the innermost nonsheathing one as already explained. 98

DISCUSSION.

De Candolle (1827) based the phyllode theory entirely on external morphology. Arber (1918) accepted the theory and put it on an anatomical basis, finding further support in the pres­ ence of inverted bundles. The theory considers the monocot- jrledonous leaf as equivalent to the leaf-base and petiole or the leaf-base only of the dicotyledonous leaf. The flattening of a petiole with a circle of vascular bundles, as seen in trana- verse section, would give rise to a concentric leaf-limb in which the adaxial bundles would be inverted. (Where the petiole has an open arc of bundles flattening would result in a bi-facial leaf, as in the case of Oxalis bujbleurifolia which has a phyllode without inverted bundlesT) If the concentric leaf were formed in this way it would be expected that the normally orientated, and inverted bundles would be sim ilar in arrangement and extent differing only in orientation as in the phyllodes of Acacia. In all the leaves examined in this investigation, the inverted bundle system was found to be much less extensive than the normal, and to differ from it in character. Arber explains this as due to a tendency to reduce the inverted bundle system. Peters (1927) points out that the presence of inverted bundles is not absolute proof of phyllodic structure. He examined the first leaves produced by young plants of Acacia cuneata and A.cyanophylla. These consist of a petiole and a rhachis bearing two leaflets. He found inverted bundles in the rhachis although the latter never forms part of the phyllode. On the other hand it is possible to have phyllodic structure without inverted bundles, as already mentioned, and Arber suggests that here the phyllode is formed by the flattening of a petiole with an arc of ' • ' " bundles instead of a circle, which results in a linear arrangement and absence of inverted bundles.

It would be expected that the inverted bundles would pass through the leaf-base and join on directly to the vascular system of the stem, as is found in petioles. The first point brought out by the present investigation is that there is no uniformity in the relationship of the two svstems. In the first type of inverted bundle system (lanthe type) there is a direct connection of this system with that of the stem. In Adamson’s ( 1 9 2 5 ) opinion the condition found in some species of Juncus do "not seem to afford any evidence for or against the phyllode theory." Even if it is admitted that this type does not offer any ohstancle to the phyllode theory, it is difficult to see how other types can be made to harmonize with it. Can the in­ verted bundles of Zephyranthes Candida, Herb. and Narcissus poeticus, L. which end in storage tracheids, be considered as forming part of an ordinary petiolar system? In considering 99

the leaves of the Agavoldeae, Arber infers that they are morphologically leaf-bases, the solid apex having petiolar structure, see page 90. But how are the inverted bundles found in the lower portion of the leaf to be explained in re­ lation to this theory?

It is possible to consider the evolution of the monocotyledonous leaf from a very different point of view. The Inverted bundle system can be considered as secondary, arising relatively late in the evolution of these leaves. The simple linear bi-facial leaf would then be primitive. fossibly two lines of evolution have taken place: (ij The leaf remained bi-faoialand evolved along lines similar to those in the Dicotylédones so that a lamina, petiole and sheathing leaf- base were differentiated. Unlike the Dicotylédones the venation of the primitive leaf was maintained with little modification in the modern form. (ii) The leaf became unifacial due to the introduction of an accessory adaxial inverted bundle system to supply the increasing extent of palisade tissue which had become concentrically arranged. In this case the inverted bundle system was formed to fu lfil a physiological need and does not result simply from the flattening of a primitively, cylindrical petiole, as the phyllode theory states. Further evolution along this line resulted in the production of a lamina petiole and leaf-base, all with inverted bundles present.

Secondary origin of vascular bundles has been described for Ornithogalum eaudatum. Ait by Lonay (1902). According to Lonay the peripheral bundles of the leaf-base are formed from procambial strands, each of which arises from a single mesophyll cell, after the general vascular system has become differentiated^ the increase i n vascular tissue of the leaf-base being necessary owing to the presence of bulbils. Thus the secondary origin of inverted bundles suggested in this account is not u n iq u e . 100

SUMMARY.

I. A description is given of the bi-facial leaf in which an adaxial assimilating tissue is in relatively close approximation to the single series of parallel vascular bundles owing to the relative thinness of the l e a f . II. The occurrence of cavities In the mesophyll, run­ ning parallel to the vascular bundles, are described.

III. The thickened plates in the mesophyll of leaves of Olivia nobilis are described. r\T, Spiral, non-lignified cells present in the mesophyll of leaves of Nerine corusca are described.

V. Only six genera of the Amaryllidaceae, besides the Conostylideae which were not investigated, have con­ centric leaves.

VI. A description is given of the mature structure of the concentric leaf in these genera. A detailed description is given of eight species of lanthe aé the evolution of the concentric leaf is indicated in transitional forms.

VII. In the genus Agave the Increase in the thickness of the leaf Is correlated with an increase in the amount of vascular tissue. The peculiar white hairs on the margins of leaves of Agave disceptata are described.

VIII. A comparision is given between Fourcroya cubensis and Beschornia Juccoides with Inverted adaxial bundles and Doryanthes excelsa with normally orien­ tated adaxial bundles.

IX. In Fourcroya cubensis and Beschornia Juccoides Inverted bundles are present in the thickened por­ tions of the base and mid-rib region of the leaf. The apices of the leaves frequently end in long solid points. Here only normally orientated bundles are present but these become concentrically arranged so that some are inverted. However these are dis­ tinct from the inverted bundles in the lower part of th e l e a f . 101

X. The behaviour of the inverted bundles at the base of the leaf, and their connection with the stem were found to vary. Three types are described:

(i) The lanthe type.

In the genus lanthe the inverted bundles are formed by the incurving of bundles of the sheathing portion of the leaf-base into the base of the leaf-limb. This may be accompanied by the loss of the adaxial surface when the leaf becomes unifacial.

(ii) The Agave type.

In Agave americana the inverted bundles are formed by branches from the normally orientat­ ed bundles. These branches move towards the adaxial surface, curve sharply and proceed vertically upwards as inverted bundles. In some leaves the median inverted bundles are derived from the stem vascular system. (iii) The Narcissus type.

In Narcissus poeticus the inverted bundles pass down from the leaf-lim b into the upper part of the leaf-base where they die out, end­ ing in groups of small storage tracheids. XI. In Zephyranthes Candida, Herb, a combination of the first and last types is found. The four or five median inverted bundles resemble those of Narcissus poeticus, each bundle ending in a group of storage tracheids. The two marginal inverted bundles are derived by the incurving of two of the normally orientated bundles of the sheathing portion of the leaf-base as in lanthe aquatica.

XII. A discussion of the Phyllode theory is given. 102

NOTE ON NOffiNCLATURE.

Certain of the specific names at present in use for the Hypoxideae are in point .of fact invalid. However it is impossible to discuss revision here, as this is not a taxomic paper. The nomemclature given in Nel*s paper (1914) in Engler^s Yahrbttcher - "Die afr ikanischen Art en der Amaryll idaceae- Hypox ideae Bd LI p.287, has been used.

(i) lanthe minuta (Linn fil) Williams. (ii)^ lanthe alba (Linn fil) Salisb.

(iii) lanthe aquatica (Linn fil) Williams.

(iv) lanthe stellata (Linn fil) Wiliams. .

(v) lanthe ova ta (Linn fil ) Salisb.

(vi) lanthe Schlechter-i (Bbl) Williams.

(vii) lanthe curculigoides (Bol) Williams.

The first five species appeared under the generic Hypoxis, Linn., in Linn fil. Suppl. 197-8, while the other two were placed by Bolus in the same genus. Hook Ic. t. 2259 A&B.

(viii) lanthe flaccida, Nel.

(ix) Hypoxis villosa, Linn fil.

ACKNOWLEDGEMENTS.

I should like to thank Mr. S. Garside for material collected in South Africa and for the five photographs, Plate I figs 2-4, and Plate II figs 1 & 2.

I should like to thank Mr. Golding for photograph, Plate I fig I, which was taken in London. The directors of the Royal Botanic Gadens, Kew and the Chelsea Physic Gardens have most kindly supplied me with m a t e r ia ls . 103 DESCRIPTION OP PLATES.

P la t e I f i g s 1 -2 HAEMANTHUS COCCINEUS. F ig 1 . B ulbs and inflorescence stalks. Stellenbosch Iffis. Pig 2. A plant with foliage leaves, growing in Bedford College green-house. P ig s . 3 - 4 . HABMANTEÎUS ROTUNDIPOLHrS. P ig 3- B u lb s, S t e lle n - bosh Plats. Fig 4. Leaves in nature, Stellenbosch Plats.

P la t e I I . P ig s 1& 2 . BRUNSVIGIA GIGANTEA. Leaves in n a tu re, Stellenbosch Plats, and Kirstenbosch, South Africa, respectively.

DESCRIPTION OF PK^RBS.

Pigs 177-180. 1 7 7 . Haemanthus coccineus. Transverse section of leaf, a - mesophyll broken down to form cavities, b = adaxial palisade, c s mucilage cell, x 155. 178. Haemanthus rotundifolius. Transverse section of leaf, lettering as in fig 1 7 7 . X 1 5 5 . 1 7 9 . Abaxial surface of same. x 155. 180. Brunsvigia Parkeri var. alba. Transverse section of leaf. X 33 VTT

Figs 181-184. Clivia nobilis. 181. Transverse section of leaf, t a plates of thickened cells, p « pltts. x s calcium oxalate crystals, x 4 O8 . 182. Diagrammatic transverse section of leaf, lettering as in fig 181. x 33 1/3. 183. Longitudinal section showing details of central thickened cells, x 408. 184. Apical portion of leaf showing venation, natural size.

Figs 185-188. 185. Sprekelia formosissima. Longitudinal section of leaf showing arm-palisade, adaxial surface, a s air space. X 408. 186. C alliphuria Hartwegiana. Leaf showing venation, X I 8 7 . Part of transverse section in median part, x 33 1/3. 188. Eucharls M astersii. Transverse section of leaf, x 408.

Pigs 189-190. Nerine corusca. 189. Transverse section , and 190 longitudinal section of leaf, showing details of spiral cells. X 4 O8 .

P ig s 1 9 1 - 1 9 4 . Bomarea caidasiana. 191. Transverse section of l e a f . X 3 3 1 / 3 . 1 9 2 . Detail of transverse section, x 408. 1 9 3 . Longitudinal section.x408. 194. Transverse section show­ ing a vascular bundle with xylem towards physiological lower sur­ face. X 408.

Pigs. 195“ 199* Mblineria recurvata. 195. Diagrammatic trans­ verse section, x 3 3 1 / 3 . I 9 6 . Stoma with subsidary cells, x 408 1 9 7 . Detail of transverse section, x 408. 198. Detail of long­ itudinal section of base of hair, x 680. 199.Detail of longit­ udinal section, s a sclerotic hypodermal cells, x 408. 104.

Pigs. 200-202. Hypoxis villosa. 200. Transverse section, with large epidermal cells shown diagrammatîcallÿ. x 33 1/3. 201. Longitudinal section showing detail of base of hair, x 408. 202. Transverse section showing detail of stoma, x 408.

P ig . 2 0 3 . Cyanella capensls. Transverse section of leaf, x 33 1 / 3 . P ig s 2 0 4 - 2 0 5 . Lanarla plumoaa. 204. Portion of trans­ verse section, x 4 O8 . 205. Diagrammatic transverse section. X 33 1 / 3 .

P ig s 2 0 6 - 2 0 7 . Zephyranthes At amas co. 20^. Transverse section of leaf. 33 1/3. 207. Detail of portion of epidermis and p a lis a d e . X 408. Figs 208-210. Narcissus. 208. Transverse section of leaf of N. Jonquillia var. jonguilloides. x3 3 1 /3 . 209. Transverse section of leaf of Ü. trlandus. 33 1/3• 210. Transverse section of leaf of N. Bulbocodium var. citrinus. X 33 1 / 3 .

P ig s 2 1 1 - 2 1 3 . Agave disceptata. 211. Transverse section of l e a f . X 33 1/3. 212. Detail of margin. x 408. 213. Detail of epidermis and peripheral mesophyll. x 4 O8 .

P ig s 2 1 4 - 2 2 0 . Beschornia Juccoides. 214-219. are of successive transverse sections from apex to base of leaf, x 3 3 1 / 3 . 220. Detail of peripheral tissues at level of fig 218. x 408.

Pigtt 2 2 1 - 2 2 3 . Doryanthes excelsa. 221. Transverse section of mid-rib, in the centre of the leaf, x 3 3 1/3. 222. Transverse section of portion of lamina wings, x 33 1/3. 223. Detail of peripheral tissues of transverse section, fig 222. x 408. P ig 2 2 4 . Fourcroya cubensis var. inermis. Transverse section of petiolar base, x I 4 .

P i g s . 2 2 5 - 2 3 5 . lanthe minuta. 225-228. Series of leaves from a single plant, natural size. 229. Transverse section of outer l e a f , 2 2 5 . X 33 1 /3 . 2 3 O. Transverse section of second leaf, 2 2 6 . X 9 0 . 2 3 1 . Transverse section of apex of second leaf. X 33 1 / 3 . 2 3 2 - 2 3 4 . Transverse sections of third leaf,227. x 33 1 / 3 . 2 3 2 . C en tre. 2 3 3 . Near apex. 234- Apex. 2 3 5 . Med­ ian portion of fourth leaf, 228. x 33 1/3•

P ig 2 3 6 - 2 5 7 . lanthe alba. 236-239. Series of leaves from a single plant, natural size. 2 4 O-2 4 4 . A similar series from another plant, natural size. 245. Transverse section of median portion of outer leaf,2 3 6 . x 9 0 . 2 4 6 -2 5 2 . x 3 3 1/3. Series of transverse sections from base to apex of solid tip of second l e a f , 2 3 7 . 2 5 3 - 2 5 6 . X 33 1/3. Series of transverse sections a t base of leaf, 243, 253. At base of leaf-1 imb to 256. in sheath­ ing leaf-base. 257. Details of peripheral mesophyll of median portion of leaf, 243. x 90. 105.

Figs 258-264- lanthe Sohlechter1. 264* Outer leaf of plant natural size. 258. Transverse section of part of sheathing leaf-base. x 33 1/3- 259-263- x 33 1/3. Series of transverse sections from the base of the leaf-lim b, 259 to the apex, 263.

F ig s 2 6 5 - 2 6 9 . lanthe aquatica. 265- Outer leaf, natural size. 2 6 6 - 2 6 8 . Transverse sections of the sheathing base, the base of the leaf-lim b, and the centre of the leaf-limb respectively, x 2 3 . 2 6 9 . Detail of transverse section at level of fig 268. x 9 0 .

F ig s 2 7 0 - 2 7 5 . Agave americana. 270. Transverse section of base of young shoot. a a outer leaf, b a inner leaf, c s inverted bundle. d = partially inverted bundle, e = root, f a meristem- atic zone, x 14- 271. Section at base of outer leaf. 272- 2 7 5 . X 3 3 1 / 3 . 'The formation of the third Inverted bundle. 2 5 7 . Transverse section .of upper part of sheathing leaf-base show­ ing the order of the appearance of the Inverted bundles, x 33 1/3#

Figs 276-281. Narcissus poeticus. 276. Transverse section of base of young shoot with two leaves shown, x3 3 1 /3 . 277. P ro - cambial strand' at the base of inverted bundle, x 408. 2 7 8 . B a s­ al tracheal mass of inverted bundle, x 408. 279. Inverted bundle, differentiated, at level of fig 2 7 6 . x 4 O8 . 280. Trans­ verse commissure passing from normal bundle to tracheal mass of inverted bundle, b, in fig 2 7 6 . x 4 0 8 . 281. Single tr ache id at base of inverted bundle, b , in transverse section, x 4 O8 .

F ig s 2 8 2 - 3 2 5 . Zephyranthes c^dida. 282-284- x 1^. 282. The base of a shoot with three foliage leaves. 283. Base of second l e a f . 2 8 4 . Base of third or innermost leaf. 285, 286, 289, 297, 2 9 3 , 3 0 0 , 3 0 1 , 3 0 3 , 3 0 4 are a series of transverse sections show­ ing the appearance of the inverted bundles in the transition r e g io n , x 2 3 . 287- Tracheal mass at base of inverted bundle No. 2 . X 4 O8 . 288. Inverted bundle No.2 at a higher level, x 4 O8 . 2 9 0 - 2 9 2 . Inverted bundle No.3 base, tracheal mass, and upper part, respectively. 294-296 . x 408. Inverted bundle No.4 base, trach­ eal mass, and upper part, respectively. 298. Detail of upper part of bundle in the sheathing portion of the leaf-base, a in f i g 2 9 7 .x 4 0 8 . 2 9 9 . Detail of marginal bundle of sheathing portion, b in fig 297. x 4 O8 . 302. Detail of same bundle, b at level of fig 3 O I. x 4 O8 . 305- Same b u n d le, b s N o.5 a t l e v e l o f f i g 3 0 4 . X 4 0 8 . 3 0 6 - 3 1 0 . X 2 3 . Similar series of transverse sections of transition region of second leaf. 3 II. Procambial strand at base of inverted bundle No.I. x 4 O8 . 312. Inverted bundle No.3 differentiated, x 4 O8 . 313- Pro cambial strand at base of inverted bundle No.4 . 314-319. Similar series of transverse sections of third leaf, from base to centre of leaf-lim b.x 3 3 I / 3 . 3 2 3 - 3 2 5 . Transverse sections of median vascular bundle of the third leaf at thè base, in the immature zone, and in the mature part of the leaf-limb, respectively, x 408. 3 2 2 .Diagrammatic representation of the vascular system, in the transition region . continuous black lines - inverted bundles, broken lines = the normal bundles. 320-321 .Ends of two Inverted bundles, a and b in The solid, x 155- 106 PLATE I.

HAEMANTHUS COCOINEUS.

nàCnAMTtiUS

F i g . l . F ig ,2 . HAEMANTHUS ROTUNDIFOLIUS

F ig .3 . F ig .4 . 107 PLATE I I ,

BRUNSVIGIA GIGANTEA,

i fa g # _ i'

F i g . l . F ig .2 ED

1 i

F ig .178.

F ig .179.

Fig.ISO.

F i g .177. CLIVIA NOBILIS.

MSmPwpîTIÏÏ^

F ig .1 8 2 .

6 V I © F ig .1 8 3 .

F ig.184. 110

F i g .185

F ig .188.

F ig .186 I l l

F ig.190. 112

BOMARIA CALMS IANA.

F ig .191.

F ig .193.

F ig .192.

F ig .194. 113

F i g .195

F i g .196.

F i g . 197.

F ig. 199

F ig .201. F ig .202. 114

CYANELLA CAPENSIS.

LANARIA PLUMOSA

F i g .205. 115

F i g . 206.

a DD

F i g . 207.

F i g .268

üiiminuu

F ig .209.

F ig .210. 116 AGAVE DISCEPTATA.

F ig.211 es

F ig.213. Q o

Qp O

F ig .212. 117 BESCHORNIA JUCCOIDES.

% ■c£

F ig .220. .216.

%

F ig .215

& F ig .218.

F ig .219. F ig .224, I ANT HE MINUTA. 119

Fig. 225 226.

0

F ig .234. F ig .233

F ig .232.

F ig .235. 120 lANTHE ALBA.

237. 238. 239.

F i g .245

F i g . 247 F i g .248

F i g . 252 F i g .249 F i g . 250 F i g ,251

ê F ig .254 F ig .253 121

%

F i g . 255.

lANTHE SCHLECHTERI

F i g . 258.

F i g .257

&

F i g .259.

F ig. 264. b

«'I

F ig .262. F ig .261. F ig .263 lAKTHE AQUATICA.

(9

y Winitf,,

F ig .268.

F ig ,269. 123

AGAVE AMERICANA.

F ig .270. 124

F ig .271.

Qn

F ig .272

F ig .273

F ig .274 125

F i g .275

X

a>.

10 KARCISSUS POETICUS.

0

F ig .280. F ig .276. 127 ZEPHYRANTHES CANDIDA

F i g .285.

ig .2 8 7

F ig .288.

291.

F ig .292. & D

%

F i g .300. 129

F ig .302.

F ig .303.

F ig .305. 130

F ig .30

311. 312.

F ig .313.

F ig .314. F ig .308.

F ig .315 F ig .309 131

miirn77Mniiiii(iiMiirTTrn

F ig .323. F ig .325.

F ig. 319.

F ig .320. F ig .321. F ig .322. 132 LITERATURE CITED IN TEXT.

Adamaon. R.S. On the leaf structure of Juncus. A. B. vol. (1925) xxxix. p .599 - 612. 1 9 2 5 . Arber. A. The Phyllode Theory of the Monocotyledonous ( 1 9 1 8) Leaf with special reference to Anatomical Evidence. A. B. vol. xxxii. 1918. Arber. A. Water plants, A study of Aquatic Angiosperms. ( 1 9 2 0) Cambridge. 1920. Arber. A. Leaves of certain Amaryllids. Bot. G-az. vol. ( 1 9 2 1) Ixxii. p.102 - 5* 1 9 2 1 . Arber. A. On the Leaf-tips of certain Monocotyledons. (1 9 2 2 ) Linn. Soc. Journ. Bot., vol. xlv. p.467 - 76. 1 9 2 2 : Arber. A. Monocotyledons, a morphological Study. (1925) Cambridge 1925. Areschoug. P.ÏÏ.C. Jemfflrande undersflkningar flfver Bladets Anatomi. (1873 - 8) K. Pysiog. SSlla. Lund. Minnessk. Art. 9. Hafniae. 1873 - 8. Baker. J.G. Handbook of the Amaryllideae, including the (1888) Alstroemerieae and Agaveae. London 1888. Candolle. A.P.de Organographie végétale. 2 vols. Paris 1827. (1827) Czapek Studien fiber die Wirkung Susserer Ruzkrâfte (1898) auf die Pflanzengestalt. I Flora Ixxx. 1898. I Duval-Jouve. J. Des Salicornia de l ’Hérault. Observations (1868) anatomiques et morphologiques. Bulletin de la Soc. Bot. de France, tom xv. p. 132 - 40. 1868. Engler.A. - Natürlische Pflanzen - Familien. 2. Auglage. Prantl.K . Band 15a. 1930. (1930) Fraine.E.de. Anatomy of the genus Salicornia. Linn. Soc. (1913) Journ. Bot., vol. xli. p.317 - 48. 1913* Goebel.K. Organographie der Pflanzen. vols I & II. 2 (1913) A uflage. Jena. 1913* 1 3 3

H alk et• A*G. Some experiments on the absorption by the (1911) aerial parts of certain salt-marsh plants. New Phyt. vol. x. No.4* 1911. Haberlandt. G. P h y sio lo g ica l P lant Anatomy. Translated from the (1 9 1 4 ) fourth German e d itio n by Montagu Drummond. London. 1914. Irmisch. T. Zur Morphologie der monokotylischen Knollen - (1850) und Zwiebelgewâchse. Berlin. 1850. Linsbauer. K. Handbuch der Pflanzenanatom ie. I. Abt. 2. T e il. Histologie. Bd. iv. Berlin. Das Tropische Parenchym. Fr. J. Meyer. 1923. Meristeme. Otto Schflepp. 1926. Die Epidermis. K. Linsbauer. 1930. 2 Teil. Hautgewebe. Die Pflanzenhaare. Fr. Netolltsky. 1932. Lonay. H. Recherches Anatomiques sur les feuilles de (1 9 0 2 ) l ’Omithogalum caudatum. Ait. M8m. de la Soc. Roy. des S ci. de Liège. Ser I I I . v o l. iv . No.9. p. 1 - 8 2 . 1 9 0 2 . Marloth. R. Weltere Beobachtungen fiber die Wasseraufnahme (1926) der Pflanzen dureh oberirdische Organe. Sonde rabdruck au s der B erichten der Deutschen Bot. Gesells. Jahrg. Bd. xliv. Heft 7. 1926. Meyer. Fr.J. See Linsbauer. (1 9 2 3 ) N el. G. Studien fiber die Amaryll idaceae - Hypoxideae (1 9 1 4 ) unter besonderer Berflcksicï-htigung der afrikanischen Art en. Erg. Bot. Jahrb. Bd. li. p. 287 - 3 4 0 . 1 9 1 4 . Netolltsky. Fr. See Linsbauer. (1 9 3 2 ) Parkin. J. On some points in the Histology of Monocoty­ (1898) led on s. A.B.V01. x i i . p . 1 4 7 - 1 5 3 - 1898.

P eter s. T. Uber die Bedeutung der Inversen Leitbflndel fflr ( 1 9 2 7 ) die Phyllodien - Theorie. Zeitschr. Wiss. Bid. Abt. E. Planta. 3 (i) P. 90 - 99. 1927. 134 Salisbury. E.J On the Causes and Ecological Significance of (1927) Stomatal Frequency with special reference to Woodland Flora. P h il. Trans. Roy. Soc. B’. vol. 216. p.l - 65. 1927. Scharf. W, BeitrEge zur Anatomie der Hypoxideen und (1893) einiger verwandter Pflanzen. Bot. Tracts, x. 1893. Schmidt. 0. Uber die Blattbau einiger xerophilen Liliiflor* (1891) en. Bot. Centralb. Jahrg. 12. Bd. xlvii. 1891. Schüepp. 0. See Linsbauer. (1926 )

Schulze. R. BeitrEge zur vergleichenden Anatomie der (1893) Liliaceen, Haemodoraceen, Hypoxidoideen und Velloziaceen. Engler’s Bot. Jahrb. Bd. xvii. p. 295 - 394. 1893. S te ln k e il. Observations sur le mode d’accroissement des (1837) feuilles. Annales des Sciences Naturelles. Sér 2. viii. p. 289.- 1837. Volkens. G. Die Flora der Aegyptische - Arabischen Wflste. (1887) Berlin. 1887. Warming. E. Oecology of Plants. , (1909) Wassermann. J BeitrEge zur Kenntnis der Morphologie der (1924) Spaltflffnungen. Bot. Archiv. Bd. v. Jan-MErz. p.20 - 69. 1924. Wiesmer & BeitrEge zur Kenntnis der Anatomie des Agave- Baer. B la t t e s ., lin Sitzungber. Akad. Wien. I. Abt. (1914) c x x i ii . 1 9 1 4 . Yapp. See Maximov. ( 1912)

Z alenskl. See Maximov. (1904) Zinke. W. Ueber der Assimilationsgewebe der Monocotylen (1924) und seine Verwendung in der Frage ihres systematischen. Bot. Archiv. Band v. Jan. - MErz. p. 7 4 - 9 1 . 1 9 2 4 e