STUDIES ON INDIAN HYMENOPHYLLACEAE Part. V. Some Developmental Stages of the Gametophyte of Mecodium badium (Hook, et Grev.) Copel. found within the Sporangium

B y U sha Sharm a Assistant Professor of Botany, Lucknow University

(Received for publication on Vay 16, 1961)

Introduction

W h ile examining some fertile material of Mecodium hadium Copel. (1938) (PI. XXXIX, Fig. 1), [Syn. Hymenophyllum australe willd. var, badium (Hooic. et Grev.) Bedd. (Beddome, 1883, 1892)] it was noticed that certain spores had already germinated within the sporangium. A careful further examination of unopened sporangia showed several such stages of germination and these constitute the subject-matter of this brirf note. So far as 1 know germination of spores inside the sporangium has not been fully recorded in Hymenophyllaceae. A three-celled stage of the gametophyte of Hymenophyllum within the sporangium has been reported by Holloway (1930, p. 272) and Stokey (1940, p. 762). Some of the figures of the early stages of the spore germination in some species of the genera Hymenophyllum and Trichomanes have been published earlier by Campbell (1918, p. 373) and Sadebeck (1902, p. 93). Detailed work has been done on the germination of spores in culture by Holloway (1930) and Stokey (1940, 1948). These papers also summarize the earlier references regarding the gametophytes of Hymenophyllaceae (Stokey, 1940 and 1948). Compeland (1938, p. 5) points out that the spores of Hymenophyllaceae germinate very promptly. In spite of this, nobody seems to have noticed the germination (at least beyond three-celled stage) of the spores inside the sporangia. The stages referred to in this paper were observed in the same material that was collected from Khasi and Jayanthia Hills of Assam in November 1959, preserved in 70% alcohol and being described in a separate paper (Sharma, 1961, unpublished).

O bservations

The spore of Af. W/wmismore or less circular having a two-layered wall with an outer ornamented exine and an inner smooth intine. The spore contents are granular and starch grains are also present (Text- F ig . 1). The earliest stage of germination is the laying down of a transverse wall which divides the spore contents into two more or less equal halves. 8 pj>5 T eXT-Fiq s . 1-14. Fig. 1. A mature spore. Fig. 2. The spore having three unequal cells. The exine can be seen peeled off. For explanation see the text. Fig. 3. Three-celled cushion having more or less equal cells. The exine of the spore wall can be seen peeled off all round. Fig. 4. A lateral view of the three-celkd gametophyte. Fig. 5. Four-celled gametophyte where one of the cells of the three-cellcd plate has divided transversely. Fig. 6. The same with longitudinal division form­ ing a four-celled plate which is a rather unusual feature. Figs. 7 and 8. Other two cells of the irregular four-celled plate have divided. InFig. 8 one ccll seemsto be trans­ formed into a thizoid. Figs. 9 and 10. Five- and six-celled gametophytes respectively. Fig. II. A lateral view of the six-celled gametophyte. Figs. 12 and 13. Seven- and eight-celled gametophytes respectively. Fig. 14. The terminal cell of one of the filaments of seven-celled gametophyte has been transformed into a rhizoid. A series of brown rims can be seen in the rhizoid (ex., exine; rz., rhizoid).

One of these enlarges and divides by a wall at right angles to the first one (Text-Fig. 2). The spore at this stage attains the form of a triangular cushion formed of three cells separated by three walls (Text-Fig. 3). But these three walls appear as though they meet in the centre and divide the spore into three parts. The exine (ex.) of the spore wall may be seen peeled off all round this triangular cushion. Each one of these three cells has its own prominent nucleus (Text-Fig. 3). A lateral view of the three-celled stage can be seen in Text-Fig. 4. One of these three cells further divides transversely (Text-Fig. 5). Sometimes this division is longitudinal and one comes across stages seen in Text-Figs. 6, 7 and 8. A stage similar to the one seen in Text-Fig. 6 observed in Hymeno- phyllum blumeanum has been interpreted as an irregularity by Stokey (1940, p. 764). Similar longitudinal divisions of the other two cells of this three-celled plate can be seen in some of the preparations. This is an unusual feature. Generally all three cells of the triangular cushion divide transversely (Text-Figs. 9 and 10). In Text-Fig. 9 the nucleus of one of the cells can be seen divided and the cells partitioned ofiF as in Text-Fig. 10. Text-Figure 11 shows the lateral view of the six-celled stage shown in Text-Fig. 10. Text-Figures 12 and 13 show further divisions of the end cells leading up to a filament of three cells at one or more angles as the case may be. Generally as has already been noticed by Stokey at about this time when one or two angles devlop a three-celled filament, the apical cell elongates, loses its cytoplasm and chlorophyll and becomes a rhizoid (Text-Figs. 14-19). Sometimes two such filaments may give rise to rhizoids (Text-Fig. 17). As in the figure the remaining four-celled filament seems to be the precursor of the gametophyte which may attain either a filamentous or a ribbon-like form. Further stages could not be made out in the material. Rhizoid formation, it has been noticed in this material, takes place usually from the third cell (Text-Figs. 14-19) but it may be sometimes from the second cell (Text-Fig. 17), or even from the fourth cell also as in PI. XXXIX, Fig. 2. In some rhizoids there can be seen a series of brown rims (Text-Figs. 14,16, 19 and PI. XXXIX, Fig. 2) most probably indicating where the inner layer has stretched beyond the enclosing layers as has been pointed out by Stokey (1940, p. 760). Plate XXXIX, Fig. 2 shows the oldest stage found in the sporangium and it measures nearly 230/i in length and is ten-celled. Here the charac- Text-Fios. 15-20. Fig. 15. A ten-celled gainetophyte with an unusual pattern where longitudinal divisions have taken place in the original three>celled plate instead of transverse divisions. Figs. 16. An eight-celled gametophyte with the third cell of one of the three filamentc transformed into ihizoid. Fig. 17. A nine-celled phyte with two terminal cell* transformed into rhizoids. Fig. 18. A ten-celled gametophyte. Apical cell of one of the filaments has divided longitudinally and the other filament terminated into the rhizoid. Fig. 19, A more or less similar type oj, stage. The foigmr cell out of the two cell* produced by the longitudinal division of the apical cell divides transversely to give rise to two cells. Thus a flattened plate 2 3 colls is formed at the apex. Fig. 20. A ten-celled gametophyte. None of the c jIIs his bi3!i tMisformsd into rhizoid and 2 cells of the original three-cclled plate hivo divided longituditially. The exino can be seen still attached to one ol the fil.tmints. For further explanation sec text, ex., exine; rz., rhizoid. leristic triangular cushion is not clear as the longitudinal division of one of the cells has rendered the plate four-celled. On one side the remnants of the outer spore wall exine (ex.) may be seen. Text-Figures 15 and 20 are rather interesting. A cursory look at them suggests that a series of transverse or oblique divisions have taken place in each cell of the original three-celled plate. But a careful study of these figures, however, shows that there may be a series of longi­ tudinal divisions also leading to a grouping which may be mistaken for transverse divisions. Thus it can be seen that though the longitudinal divisions of the cells of the triangular cushion are not as common as the transverse ones, yet. they are of quite frequent occurrence and fairly developed gametophytes have been found having this type of rather unusual pattern. In Text-Fig. 20 remnants of the exine (e.v.) can still be seen on one side of the gametophyte. Although the gamefophyte h ten-celled, none of these cells has been transformed into a rhizoid.

No clear apical meristem is seen difl'erentiated in the gametophytes found so far in the material as is quite clear from Text-Figs. 1-20. But some longitudinal divisions appear first in the terminal cells of one of the three filaments favourably placed (Text-Fig. 18). The bigger cell out of these two cells thus formed shows two nuclei and an in­ complete, faint cytoplasmic wall can be seen separating them. This division is complete in Text-Fig. 19, sometimes this division may occur in the penultimate cell of the filament (Text-Fig. 17). The cell plate has not yet been laid and only the nucleus has divided into two. 1 do not know if these stages indicate a kind of initiation of an apical meristem (see Stokey, 1940, p. 766). Plate XXXIX, Fig. 3 shows some of the early stages of spore germi­ nation, having 3 to 8 cells. These gametophytes can be seen contained inside a sporangium (PI. XXXIX, Fig. 4).

No hairs have been found on the gametophytes of M. badium. This observation is in conformity with that of Stokey’s observation that there are no hairs on the gametophyte of Hymenophyllaceae (I960).

Stokey and others think that the gametophytic growth is very slow; not only in comparison with the quick germination of spores but also in comparison with the development of the gametophytes of other leptosporangiate ferns. It seems, therefore, rather surprising that spores have germinated into ten-ceiled gametophytes inside the sporan­ gium itself.

The gametophyte of Mecodium hadium (Hook, et Grev.) Copel. seems to resemble mostly those of HymenophyUum (Stokey, 1940) and Trichomanes reniforme (Holloway, 1930). A cknowledgement The author is highly grateful to Dr. A. R. Rao for his kind and valuable guidance during the course of the present investigation.

R e fe r e n c e s

B eodom b, R. H. 1883, 1892. Handbook to the Fents of British India with Supple­ ment. Calcutta.

C a m pb el l, D. H. 1918. The Structure and Development of Mosses and Ferm. 3rd Ed. The Macmillan Co., New York.

C o pel a n d , E. B. 1938. Genera Hymenophyllaceanm. Philipp. J. Sci. 67; 1-110.

H o llow ay, J. E. 1930. The experimental cultivation of the gametophytes of HymenophvUum pulcherrimuni Col. and Trichomanes reniforme Forst. Ann. Bot., Land. 44: 269-84.

S a d eb e c k , R. 1902. Hymenophyllaceae in Engler and Prantl’s Nat. Pflanzen- familien. Teil I. Abt. 4. Verlag von Wilhelm Engelmann, Leipzig. SloKEY, A, G. 1940. Spore germination and vegetative stages of the gametophyles of Hymenophyllum and Trichomanes. Bot. Gaz. 101: 759-90. — - . 1948. Reproductive structures of the gametophytes of Hymenophyllum an d Trichomanes. Ibid. 109: 363-80. 1960. Multicellula* and branched hairs on the fern gametophyte. Amer. Fern. J. 50(1): 78-87. SharMa, U. 1961. Studies on Indian Hymenophyllaceac. IV. Contributions to our knowledge of Mecodium badium (Hook, et Grev.) Copel. (Unpublished). * Not seen in original.

Explanation of Plate XXXIX

Fig. 1. An entire plant, XO’6. Fio. 2. A tei-celled gametophyte with one of its terminal cells modified into a rhizoid, x486. Fia. 3. G.imstophytes of different stages from 3-8 cells, x200. Fia. 4. The gametophytes found inside the sporangium, xl40. {an., annulus; ex., exine; gam., gametophyte; rz., rhizoid.)