Morphology of the Prothallus and Juvenile Sporophytes of Some Species of Dryopteris

Proc. Indian Acad. Sei., Vol. 85 B, No. 2, 1977, pp. 48-52.

Morphology of the prothallus and juvenile sporophytes of some species of Dryopteris

SURJIT KAUR National Botanic Gardens, Lucknow 226001

MS recoived 27 May 1974; in final form 22 November 1976 ABSTRACT Prothalli and juvenile sporophyte of seven species of Dryopteris are describea. Spore germination is of Vittaria-type and prcthallial development is oI the Aspidium-type with the characteristic range of variations in the aifferent species.

1. INTRODUCTION DRYOPTERIS Adanson is a large and widespread genus of the Dryopteri- daceae (subfamily Dryopteridoideae), and several natural groups of species are recognized within the genus. Though the prothallus of D. filix-mas is one of the earliest fern prothalli described,1 the prothallial morphology of this large genus is largely unknown. A few details of prothallial morphology of some Japanese species are described by MomoseL3,4 and of D. ludovi- ciana by Cousens and Homer. 5 Duncan e described apogamy and apogamous development of embryos in some species. The juvenile sporophyte of the genus is practically unknown. Since Dryopteris is a very large and diversi- fied genus it will be worthwhile to record the prothallial morphology of as many of its species as possible. Also, such a study would make it possible to compare the prothalli of Dryopteris with those of the other genera of the group like Acrophorus, ~ Arachniodes, Cyrtomium, s Didymochleana, 9 Peranema, ~ Polystichum 1° and Woodsia, 11 the prothalli of which are already described in literature. The present study concerns seven species, viz., D. borreri Newm. D. carthusiana (Vill.) H. P. Fuchs, D. cochleata (Don) C. Chr., D. hirtipes (B1.) O. Ktze., D. filix-mas (L.) Schott, D. marginata (Wall.) Christ and D. sino-fibrillosa Ching. Spores of D. cochleata and D. sino-fibrillosa are collected from South India, D. hirtipes from Assam and those of D. marginata from Charkrata. Spores of D. borreri, D. carthusiana and D. filix-mas were procured from Belgium. The spores were sown on Knop's medium solidified with agar12 in petridishes and cultures were maintained at 23-26° C and ca 600 fte. light intensity.

48 PROTHALLIAL MORPHOLOGY OF Dryopteris 49

2. PROTHALLIALDEVELOPMENT

The spores germinate in 10-15 days after sowing. Germination of the spore (figure 1) is of the Vittaria-type z3 as in other Dryopteridaceae z4 but

(Captions given in page NO. 52) 50 SuRJrr KAUIt

just after the first division, the prothallial cell cuts eff two or three rhizoid initials so that the germ filament has two to four rhizoids (figures 2, 3). Soon a germ filament 4--8 cells long is produced (figure 4) before divisions start. in other planes. In many cases (especially in D. cochleata) the basal cell produces another germ filament and occasionally it gives an impression that more than one filament emerges from a single spole (figure 5).

The prothallial development is of the Aspidium-type and the full range of variations characteristic of the type are seen in different prothalli. In most of the cases (D. borreri, D. carthusiana, D. filix-mas and D. marginata) the terminal cell of the majority of germ filaments ends in a unicellular papillate hair (figure 6) and the formation of an obconical meristematic cell is initia- ted in one of the penultimate cells, often second or third from the terminal cell (figure 7). In D. carthusiana and D. marginata the terminal cell, sometimes divides by a longitudinal wall in such a manner that the terminal hair gets seated on one of the daughter cells (figure 8). An obconical meristematic cell is then formed in the sister cell of the hair bearing daughter cell by a wall oblique to the wall separating the two daughter cells (figure 9)or by more than two walls the last two being oblique to each other (figures 10, 11). Sometimes the meristematic cell is established only when the prothallial plate becomes three or four cells broad in D. marginata (figure 17). In some cases (especially D. sino-fibrillosa) the terminal cell of the germ filament ends in a hair and formation of the meristematic cell is considerably delayed. In majority of the cases in D. cochleata, D. filix-mas and D. marginata, the terminal cell divides longitudinally after producing a hair and the daughter cell devoid of the hair develops into a broad pluricellular lobe (figure 16) in one of the marginal cells of which a meristematic cell is formed. In such cases the hair bearing cell protrudes prominently as a conical emergence. In species like D. carthusiana, D. cochleata and D. marginata, the germ filament does not terminate in a hair (figure 5); the terminal cell (figure 13) or the penultimate cell (figure 12), in such cases divides longitudinally initiat- ing plate formation. In the former case, one of the daughter cells divides by a wall oblique to the first wall to form a meristematic cell (figures 14, 15). When the prothallial plate is formed by the penultimate cell, the first division in the penultimate cell may be longitudinal (figure 12) or oblique as often in D. cochleata and D. marginata. In the course of development of the prothallial plate, 2-6 (commonly 4 or 5) ceils in the posterior region of the germ filament remain uniseriate (figures 7, 17, 18). After the establishment of the meristematic cell, growth of the young prothallus is quite rapid and soon the anterior margin becomes notched at the meristematic region, with the meristematic cell located at the PROTHALLIAL MORPHOLOGY OF Dryopteris 51 base of this notch (figure 18). Tile identity of the meristematic cell is maintained till quite late, a stage when the prothallus becomes nearly cordate (figure 20). Tile meristematic cell is then replaced by a pluvicellular meristem (figure 21)in the usual way (i.e., by a transverse division in the meri~tematic cell and then successive longitudinal divisions in the outer daughter cell). Marginal hairs are profuse by the time tile prothallus becomes cordate. The hair-bearing marginal cells often protrude out of the margin and thus the margin of the young prothallus becomes irregular (figures 20, 21). Soon superficial hairs similar to the marginal ones also develop. Some of the superficial hairs may be two celled (figure 24). The formation of a midrib in tile young prothalli starts about three months after spore germination and the prothalli attain maturity about 4 months from spore germination.

3. MATURE PROTHALLUS

Mature prothallus (figure 22) is of the cordate type with a prominent thick midrib, bearing rhizoids and sex organs on file lower surface. Anthe- ridia may also be borne marginally when the prothalli grow crowded. The wing cells are uniformly thin walled. Unicellular, papillate, capped hairs (figure 23) occur all over the margin and both surfaces; hairs are more profuse on the lower surface.

Antheridia are subglobose with tile basal cell short and funnel-like (figure 27). Usually they are sessile and in some species like D. borreri and D. filix-mas, some of the anthevidia may become stalked. Antheridium is developed from an antheridial initial (figure 25) which divides by a transverse wall to separate a basal cell and an outer cell (figure 26). The oper- cular cell is single. Archegonia are formed towards file maturity of the prothalli, when the midrib is already established. Archegonial neck consists of four tiers of cells and is four or five cells long, sometimes being slightly swollen towards the apex.

4. JUVENILE SPOROPHYTE

First juvenile leaf is obcuneate, lobed and with a single vein which dichotomises more than once, so that each lobe corresponds to a branch of file primary vein (figure 28). A midrib is formed by file fourth or fifth leaf, its origin being from one of the daughter veins of the first dichotomy (figure 29). Later tile midrib bears lateral veins alternately (figure 30) and soon these branch pinnately (figure 31). The lamina becomes lobed corresponding to the venation, and later pinnate. Unicellular papillate hairs similar to those present on the prothalli, though more elongated, occurs 52 SURJIT KAUR

profusely on the surface and margin of the juvenile leaves. Such hairs are also reported in other dryopteridoid genera like Peranema. ~ Similar hairs also occur on the stipe and leaf base of the juvenile leaves. The hairs are progressively longer on the successive juvenile leaves.

ACKNOWL~GEMEN~ Thanks are due to the authorities of Experimental Gardens, University of Bruxelles, Belgium, who supplied spores of three species of Dryopteris used in this study and to Dr T. N. Khoshoo, Director, National Botanic Gardens, for encouragement.

REFERENCES 1. Kny, L., hot. 1Vandt. 9 411 (1895). 2. Momose, S., J. Jpn. Bet. 13 113 (1937). 3. Momose, S., J. Jpn. Bet. 14 445 (1938). 4. Momose, S., J. Jpn. Bet. 15 280 (1939). 5. Cousens, M. I. and Homer, tL T., Am. Fern J. 60 13 (1970). 6. Duncan, H. F., Bet. Gaz. (Chicago) 105 202 (1943). 7. Nayar, B. K. and Kaur, S., Bet. Not. 119 1 (1966). 8. Chandra, P., Ph.D. Thesis, Agla Univeisity, Agra (1969). 9. Stokey, A. G. and Atkinson, L. R., Phytomorphology 4 310 (1954). 10. Nayar, B. g., Kaur, S. and Claanctra, P., Prec. Indian Aead. ScL B49 198 (1968). 11. Kaur, S. and Chandra, S., Phytomorphology 23 171 (1973). 12. Nayar, B. K., Bet. Gaz. (Chicago) 123 223 (1962). 13. Nayar, B. K. and Kaur, S., J. t"alyn. 4 1 (1968). 14. Nayar, B. g. and Kaur, S., Bet. Rev. 37 295 (1971). 15. Nayar, B. K. and Kaur, S., Phytomorphology 19 I79 (1969).

EXPLANATION OF FIGURES Figures 1-31. 1. Germinating spore of Dryopteris cochleata showing Vittaria-typ¢ spore germination. 2, 3. Same, showing mole than 2 rhizoids. 4. Gem- filament of 1). marginata. 5. Two germ filaments en~erging from a single spo, e of D. cochleata. 6. Germ filament of D. cochleata showing terrrinal hair. 7. Young prothallus ofD. borreri showing formation ofmeriste- matic cell. 8, 9. Germ filaments of D. carthusiana showing foimation of reeristerratic cell in the terminal cell. 10, 11. Young sleatulate prothalliof D. marginata. 12. Germ filament of D. marginata showing initiation of plate formation in the penultimate cell. 13. Germ filament of D. carthusiana showing initiation of plate formation in the termiral cell. 14, 15. Young prothalli of D. marginata (14) and D. cochleata (15) showing formation of teiminal meristematJc cell. 16. Young non-meristic prothallus of D. cochleata. 17. Young plotlaallus of 1). marginata showing delayed formation of the laterally placed meristen-atic cell. 18, 19 and 20. Young cordate prothalli of D. borreri (18), 1). filix-mas (19) and D. marginata (20). 21. Apex ofn~atttre prothaUus of D. marginata showing plmicellular meristem. 22. Mature prothallus of O. carthusiana. 23. Marginal hair on the prothallus of 1). sino-fibrillosa. 24. Two-celled super. ficial hair on the prothallus of D. carthusiana. 25, 26. Stages in development of antheridia of D. marginata (25) and D. botreri (26). 27. Mature antheridium of D. filix-mas. 28-31. Successive juvenile leaves of D. J~ltx-mas. (a, meristernatic cell; h, hair; m, pluriceUular meristem ; s, spore.)