Proc. indian Acad. sci., Vol. 81 B, No. 4, 1975, pp. 174-180

Floral sclereids in some

A. M. BENDRE School of P&nt Morphology, Meerut College, Meerut 250001 MS received 21 August 1974; after revision 8 January 1975 (Communicated by Prof. V. Purl, F.A.SC.)

ABSTRACT

Sclereids have been described in the floral organs of Strychnos samba Duvign., Anthoeleista schweinfurthii Gilg., A. vogelii Planch., congesta R. Br. and spinosa Ruiz et Pay. of the 33 taxa of Loganiaceae examined. In this paper distribution, structure and ontogeny have been described. The importance of floral sclereids in the taxonomic evaluation of the family Loganiaceae has been pointed out.

INTRODUCTION

THE presence of sclereids has been reported from various organs belonging to close as well as distantly related families. Incessant inquiry into sclereid morphology and ontogeny has resulted in considerable litera- ture on the sclereids. However, only the foliar sclereids have received much attention while those occurring in other plant organs have remained ignored. Only a few studies have appeared on the floral sclereids 1-7. Taxonomic significance was assigned to the floral sclereids in Fagraea 1 wherein three species were separated on the basis of distribution and structure of the floral sclereids. The present study extends to other species of the family wherein floral sclereids were found to occur.

MATERIALS AND METHODS

The materials examined consisted of the following 33 taxa, viz.,* Gelsemium rankinii Small, G. sempervirens (L.) Jaume Saint-Hilaire, Mostuea batesii Bak., M. hirsuta (T. Anders ex Benths. et J. D. Hook.), Cynoetonum mitreola L., Mitreola alsinioides R. Br., Strychnos eolubrina L., S. doliehothrysa Gilg. ex Onochie et Hepper, S. icq/a Baill., S. innoeua Del., S. nux-vomica L., S. samba Duvign., S. spinosa Lam., Gardneria ovata Wall., Anthoeleista sehweinfurthii Gilg., A. vogeBi Planch., R. Br., N. floribunda Benth., Gomphostigma virgatum (L.f.) Baill., Buddleia alternifolia Maxim., B. asiatica Lour., B. brasiliensis Jacq. f., B. eandida Dunn., B. colvelei Hook. f. & R. Thorns., B. eolvelei var. howth castle Hook. f.,

174 Floral sclereids in some Loganiaceae 175

B. crispa Benth., B. davidii Franch., B. globosa Hope, B. lindleyana Fort. B. madagascariensis L., B. nivea vat. yunnanensis Rend. & Wils., B.pani- eulata Wall., and Desfontainia spinosa Ruiz et Pay. Of these, floral scle- reids occurred in only five species (table l) which were further examined. The floral organs were macerated following Tomlinson's technique 8. The macerated parts were mounted in glycerin jelly and slides were sealed with wax. The studies were supplemented with the observations from clearings 9 of the floral organs and also from the paraffin sections, 10/z to 12t~, and stained with safranin-fast green and haematoxylin-fast green combinations.

Table 1. Species in which floral sclereids occur

No. Name of the species* Ptace Source

1. Strychnos samba Duvign. .. Cameroun, South A. J. M. Leeuwenberg 2. Anthocleista sehweinfurthii Gilg. Cameroun, South Africa A. J. M. Leeuwenberg

3. A. vogelii Planch. .. Cameroun, South Africa A. J. M. Leeuwenberg 4. Nuxia congesta R.Br. .. Peddie, South Africa The Director, National Botanic Gardens, Kirstenbosch Desfontainia spinosa Ruiz et Pav. Royal Botanic Gardens, J. Keenan Edinburgh, U.K.

* Arrangement after Solereder (1895) l°.

OBSERVATIONS

Distribution

Pedicel and receptacle.--In the pedicel sclereids are scattered throughout the inner part of the cortex and the pith (figure 1). Generally these are absent from about 3-4 hypodermal layers, though at a few places arms of the sclereids may reach up to epidermis (Anthocleista sehweinfurthii and A. vogelii). They gradually increase in number towards the receptacle, forming aggregates at a few places which are smaller in Desfontainia spinosa and Anthoeleista voge#i, being composed of 2 to 10 cells. In Nuxia eongesta and Desfontainia spinosa sclereids form almost a complete ring on the outer side of the vascular cylinder which in the former is 2 to 5 cells deep. Calyx--The sclereids are irregularly scattered in the sepals and occur mostly in small aggregates (figures 2-4). Their number gradually decreases upwards being absent from the tip. In Nuxia congesta, however, the number of sclereids increases upwards where they occupy almost the entire sepal except the abaxial epidermis, while in all others only a few 176 A.M. BENDRE sclereids occur 2 to 3 layers above the adaxial epidermis. In N. congesta vascular bundles in the sepals remain completely surrounded by the sclereids. Corolla--Scattered sclereids occur in petals. The number is lesser than in sepals. They are generally present at the base of petals and dis- appear as soon as petals are differentiated from the receptacle. In Anthocleista schweinfurthii sclereids occur throughout the length of petals and are abundant towards the upper part in the form of large aggregates. These are mostly confined to the adaxial half being absent from the abaxial one. Androecium--Only in A. schweinfitrthii and A. vogelii sclereids occur in the walls of the anthers. While they are abundant and diffuse in the former, they are scanty and restricted only to the region near the wall in the latter. In both the cases sclereids are always located away from the line ofdehiscence. Gynoecium--Strvchnos samba and Des[bntainia spinosa reveal sclereids only in the ovary wall after ovules have fully developed (figure 5) while in Anthocleista schweinfurthii and A. vogelii sclereids occur even at a much earlier stage. They are confined to 4-5 layers inner to the wall forming an almost uniform zone. These are either single or occasionally form aggre- gates of 3 to 4 cells. In A. schweinfi~rthii sclereids occur in the style also, lying about 2 to 25 layers inner to the outer wall. The number almost remains the same up to the stigma where sclereids spread up to the walls. On the basis of shape, size and structure, sclereids in the floral organs are classified 11 as follows: The sclereids are either unbranched or branched. Unbranched cells show only protuberances or bulges. If branched, branches spread into all the directions and terminate into blunt or sharp points. The tips may further be forked into 2 to 3. The shape differs from simple-spheroidal to bone-like. The size varies considerably and sclereids range from small and narrow to very long and broad. The walls are thick and lamellations are mostly parallel. The pits are distributed throughout the wall surface and are oval, elliptical or rounded. Pits form the base of pit canals which are simple or branched. The lumen is extremely variable, retaining cyto- plasm and a nucleus till a comparatively late stage of maturation. Brachysclereids (figures 9-11): These sclereids are generally small in size either spheroidal, lobed, angular or isodiametric. The walls bulge in a few cases but distinct branches are not formed. The walls are thick and lamellations are parallel with numerous pits and pit canals. The oval- elliptical pits are distributed irregularly. The pit canals are narrow and rarely branched. A broad lumen is filled with unvacuolated cytoplasm and Floral sclereids in some Loganiaceae 177

; mm : 2 s

IO

-, ..... 17

19 21 22.

2:3 24 25 ...,;: 26 27

Figures 1-27. Fig. 1. T.s. pedicel of D. spinasa to show distribution of sclereids. Fig. 2. T.s. sepal to show sclereids in intercellular spaces in A. schweinfurthii. Figs. 3-4. T.% se-as from base upwards showing sclereid distribution in A, schweinfurthii. Fig. 5. T.s. ovary of S. samba to show sclereids in the wall. Figs.6 -8. Sclereids in T.s. to reveal the structure. Figs. 9-11. Types of braehysclereids observed. Figs. 12-16. Osteosclereids from floral organs to show structure, Figs. 17-20. Astrosclereids from various floral organs. Fig. 21. Sclerdd initial. Figs. 22-28, Sclereid mitials in the process of intrusive growth. Fig. 27. Sclereid with secondary wall deposition. (B., Branch; L, Sclereid initial; Is., Intercellular space; L,, Lamellations; P., Pits; Pc,, Pit canals,; SW,, Secondary wall; W., Wall).

B 3--April 75 178 A. IV[. BENDRE Table 2. Distribution of sclereids.

I | i i i i Species Pedicel Reeep- Calyx Corolla Andre- Gyno- tacle ecium ecium

1. Strychnos samba .. X X X X X F 2. Anthocleista schweinfurthii A A A A A F

3. A. vogelii .. A A A A F F

4, Nuxia eongesta .. A F A X X X

5. Desfontainia spinosa .. F F F F X X A = Abundant; F = Few; X = Absent. nucleus. This type of sclereids were observed in the receptacle, sepals, petals, anther walls, ovary wall and stigma. Osteosclereids (figures 12-16): The cells are considerably elongated, profusely branched and branches are borne either on the lateral sides of the body or ultimate ends. The lateral branches are small projections which terminate into blunt or sharp ends. The walls are thick and lamellated with numerous small, elliptical to oval pits and branched pit canals. Lumen is longer than broad and sometimes very much reduced. The nucleus is present even during later stages of maturation. These occur abundantly in all the floral organs. Astrosclereids (figures 17-20): The body of these sclereids is very broad from which branches of variable lengths diverge in all the directions. The branches become further forked and generally terminate into sharp ends. The wall of variable thickness is lamellated and exhibits numerous pits and branched pit canals. The size and shape of the lumen varies in accordance with the character of branching. A distinct nucleus and dense cytoplasm fills up the lumen. Astrosclereids occur in the receptacle, sepals, petals, anther wall, style and stigma.

De velopmen t

The pattern of development is similar in all the ca.ses. The following account illustrates the development of sclereids in Anthocleista vogelii. Any parenchymatous cell acts as an initial (figure 21) which lies close to intercellular spaces. It is conspicuous from the neighbouring cells due to its larger size, dense cytoplasm and a prominent nucleus. Ultimate form of the initial is determined during its individualistic growth. The size of the initial continues to increase while secondary wall deposition also takes place concomitantly (figures 22-24). In case, Floral sclereids in some Loganiaceae 179 intercellular space is available, initial gives out protuberances which enter the neighbouring spaces (figures 24, 25). A few of these develop into thin and slender branches, the length of which is determined by the extent of intercellular space (figure 26). A few to several branches may develop within a single intercellular space (figure 27). The deposition of secondary wall is differential and pits and pit canals are formed (figure 27). Once the walls attain a certain thickness, further growth ceases completely. The cytoplasm and nucleus are still seen.

DISCUSSION

During the present studies three categories of floral sclereids are recognised11; brachysclereids, osteosclereids and astrosclereids. Amongst these are also included many structural intergradations whose categori- zation under one group or the other is a matter of choice and convenience. Much has been done to arrive at a sound classification of sclereids since Tschirch 11 who recognised four main categories; brachysclereids, macro- sclereids, osteosclereids and astrosclereids. Continued discovery of numerous typological variations from those recognised by Tschirch prompted subsequent workers to enunciate new terminology (see ref. 12-14). Of the numerous terms propounded to date, many are based on morphological characters which fail to incorporate the intergradations. It was contended, therefore, that morphological characters alone may not be sufficient and hence ontogeny should also be considered15. There had been attempts to use ontogenetic characters 16. However, the fact that the physiological conditions exert a precise control over the determination of the sclereid initial which can be experimentally manipu- lated ~7-~9 indicate relatively less significance than can be assigned to sclereid initial and its subsequent developmental behaviour for the purpose of classification. The structure, ontogeny and distribution appear to be of limited use in building up a classification. So far, in view of the accumulated termi- nology, the final form attained by the sclereids seem to be the only character of some value in categorization of the sclereids. Rat and Bhupal ~3 have given such a detailed typology which incorporates most of the inter- gradations and is the most satisfactory. The value of foliar sclereids in distinguishing species within the has been fealised by many workers. Bendre I had pointed out variations in the distribution to the floral sclereids in three species of Fagraea. Morley ~, 6 used floral sclereids as one of the characters while evaluating the Melasto- maceae. Hence, it shall be worhwhile if data on floral sclereids from other,

B 4--April 75 180 A.M. BENDRE

species of the family associated with criteria of known taxonomic significance are used to consider the ' artificial assemblage' of the genera in this family. On the basis of distribution and structure of floral sclereids the following key can be drawn to differentiate the taxa studied. I. Sclereids present in all the floral organs; occur in the flower bud also. (a) Numerous sclereids, in all the parts of floral whorls except filament Anthocleista schweinfurthii (b) Sclereids few, absent from upper part of the ovary, style and stigma A. vogelii II. Sclereids present in only a few of the floral whorls; occur when flower is mature. (a) Sclereids few, absent from androecium and gynoecium, all the three types known Desfontainia spinosa (b) Sclereids numerous, in the calyx only, brachysclereids Nuxia congesta (c) S~lereid~ oaly a feet, oaly in t'l.~ ovary wall, after fertilizati~a small, brachysclereids Strychnos samba

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