THE PROTHALLI of SOME POLYPODIACEAE-II Lepisorus Loriformis, L
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THE PROTHALLI OF SOME POLYPODIACEAE-II Lepisorus loriformis, L. thunbergianus. Polypodium vulgare and Wealherbya accedens B y B. K. N ayar and F. R aza (National Botanic Gardens, Lucknow) (Received for publication on January 30, 1969) INTKODUCTION In a series of earlier communicalions, we described the proihalli ot ca. 20 genera of ihe Polypodiaceae. These and information on three other genera of related ferns (Bajpai, 1964; Orth, 1936; Schmelzeisen, 1931; Stokey, 1945; Stokey and Atkinson, 1954) available in literature indicate that prothallial morphology is perhaps more significant in an understanding of the phylogeny and evolutionary process in this family than in other groups of ferns. Among the Polypodiaceac, prothallial morphology of the subfamilies Pleopellidoideae and Poly- podioideae (Nayar, 1970) are even today little known, the majority of taxa of which the prothalius is known belonging to the Microsori- oideae, Crypsionoideae and Platycerioideae. The present account deals with the morphology and development of the prothalius in three species of the Pleopeltidoideae [Lepisorus loriformis (Wall.) Ching, L. ihuiibergiatius (Klf.) Ching and Weatlierbya accedens (Bl.) Copel.] and one of Polypodioideae {Polypodium vulgare Linn.j. For this study, spores of IV. accedens were obtained from Java, and of P. vulgare from Brussels; those of both the species of Lepismus were collected in India from the Khasia Hills of Assam. Prothalli were raised on sterilised nutrient agar medium in peiri dishes maintained at 24;h2“C. and ca. 600 ft-c. light intensity (Nayar, 1962), the light source being a set of fluorescent lamps placed vertically above the culture dishes. Spore morphology of these and several allied species is already described in detail earlier (Nayar and Devi, 1964). O bservations Spore germination and prothallial d e v e lo p m e n t. spores of all the species are of the bilateral type devoid of any perine and with the exine bearing verrucoid excrescences. Fresh spores contain palc- green plastids and prominent yellowish oil globules. On sowing they germinate rather slowly, the germ filaments emerging in 3-4 weeks. Spore germination is of the Vittaria-type (Nayar and Kaur, 1968) 6 All rhizoids are non-chlorophyllous and with their wall light-brown in colour. The germ filaments of L. loriformis are often branched, sometimes profusely, and the branches develop into separate prolhalli; occasionally the terminal cell of the germ filament stops growth and produces a terminal rhi^oid before branches are produced by the cells behind it, recalling the condition in Christiopteris (Nayar, 1967). Development of the prothallial plate is initiated when the germ fila ments are four or five cells long in W. accedens and usually 6-8 cells long in the others. There is a strong tendency in both the species of Lepisorus (more marked in L. loriformis) for prolongation of the fila mentous stage, particularly under crowded conditions of growth. Prothallial development (Figs. 1-8) is of the Drynaria-type (Nayar and Kaur, 1969) except in L. loriformis in which it is of the Kaulinia- type (Figs. 10, 11). The posterior half of the germ filament, consisting generally of 3 -5 cells, remains uniscriate; in L. thunbergianus all except the basal cell may occasionally divide longitudinally once. In those with the Drynaria-type of development, an obconical meristematic cel! is established when the proihallus is five or more cells broad at the apex (Fig. 5); it is sluggish and soon replaceri by a multicellular meristem in W. accedens and L. thmhergiams, but plays a dominant role in prothallial development and usually persists till the thalli are cordate in P. vulgare (Fig. 7). Young cordate prothalli of P. vulgare and W. accedens are short and broad (Fig. 6), becoming slightly broader than long and bearing superficial rhizoids when the thalli are ca. 1 weeks old. The prothalli of L. thunbergianus become elongated and nearly strap-like before its anterior end expands; young prothalli, often up to ca. 1 weeks old (Fig. 13), are narrow with nearly parallel sides and a notched apex, and produce clusters of marginal rhizoids as in Lepisorus excavatus (Nayar, 1961). As in L. excavatus the anterior end of the thalli be comes distinctly cordate in ca. 6-7 weeks after spore germination. The young piothallus of L. loriformis, on the other hand, develops a narrow, elongated, ribbon-like form (often 4-6 x 1-1-5 mm. in size, in ca. three months from spore germination), with parallel sides, a rounded apex (Fig. 10) and clusters of marginal rhizoids, recalling the prothalli of Kaulinia, Colysis and Leptochilus (Nayar, 1962, 1963 a, b). Some times they are branched, the branches developing as broad, ribbon like protuberances close to the apex of the thallus. There is no organised meristem (Fig. 11) till the thallus is 12-15 weeks old, when its apex becomes notched and a group of 4 6 marginal cells at the bottom of the notch become radially elongated (Fig. 13) and actively meristematic, resembling the cells of the apical meristem in the cordate prothalli of the other species. The apex of the prothallus broadens slightly but not as conspicuously as in L. thunbergianus. Prothalli of all the species develop a median midrib soon after the apex becomes cordate and a multicellular meristem is established. Adult prothallus.—In all the species except L. loriformis, the adult prothallus is of the cordate type. It is slightly longer than broad with Fiof!. 1-16. Fig. 1. Germ filament of L. thimbergianus. Fig. 2. Initiation of plale formation in the germ filament of iV. acccdens. Figs. 3, 4. Stages in the development of a spatulatc prothaliial plate in W. uccedens (Fig. 3) and L. thun- hergianus (Fig. 4). Fig, 5, Young prothallus showing cstahlishment of a meriste- matic ccll in L. Ihiinhergiunm. Fig. 6. Young prothallus of W, accvdens showing development of a cordate apex. Fig. 7. Apex of young cordate prothallus of P. vulgare showing apical meristcmatic cell and marginal hairs. Fig. 8. Young prothallus of L. thunbergianus, ca. 7 weeks old. Fig. 9. Adult prothallus of L. thunbergianus. Fig. 10. Young strap-shaped pro/hallu.v (ca. 3 months old) o f L.loriformis. Fig. 11. Apical region of the same showing lack of organised meri- stem. Fig. 12. Adult prothallus of L. loriformis. Fig. 13. Apical region of the same showing meristem. Fig. 14. Papillate prothaliial hair of P. vulgare. Figs. 15, 16. Multicellular prothaliial hairs of L. tluinbergianus (Fig. 15) and W. accedens (Fig. 16). a broad light midrib (4-6 cells thick), a deeply cordate apex and slightly rufBed wings in P. vujgare. In W. accedens it is distinctly longer than broad, with a shallowly cordate apex, a thin (3-5 cells thick) narrow midrib and flat wings having collcnchyma-likc thickenings at the cor ners of the cells; the thalli continue to elongate and some of the old thalli may become nearly strap-like and have irregularly lobed wings. The adult prothallus of L. thunbergianus (Fig. 9) is elongate-cordate, with a narrow elongated posterior end and broad shallowly cordate apex. The midrib is three or four cells thick and light, and the wings are unruffled. The adult prothallus of L. loriformis is much elongated and ribbon-like (Fig. 12) but with a shallowly cordate apex, and is similar to the prothalli of Lepisorus normalis {Pleopeltis normalis— Nayar, 1962). The midrib is 2-4 cells thick, narrow, irregular and often discontinuous; the posterior region of the prothallus remains one cell thick, never developing a midrib. Adult prothalli of all the species are hairy; hairs are very sparse and restricted to the lower surface in the midrib region in L. loriformis while they are more abundant and are both marginal and superficial in others. As in other Polypodiaceae, unicellular papillate secretory hairs (Fig. 14) and club-shaped uniseriate multicellular hairs (Figs. 15, 16), often bearing unicellular papillate branches on the stalk cells, occur mixed on the surface; papillate hairs occur marginally also. In JV. acccdens hairs are rather sparse and mostly lestricted to the anterior margins; hairs are rare in the midrib region. The multicellular hairs are usually small with a unicellular stalk, a swollen terminal cell and a lateral papillate unicellular branch on the stalk cell. The stalk is very small and discoid in W. accedens (Fig. 16). In L. thunbergianus, however, the terminal cell is often not swollen and the stalk is some times three or four cells long as in Microsoriiiin (Nayar, 1963 a) and Pyrrosia (Nayar and Chandra, 1965). In L. loriformis papillate hairs aie sometimes absent, though on some thalli a few are found on the lower surface of the midrib. Whereas multicellular hairs are pro duced only at maturity, papillate hairs are produced from early cordate stage of development onwards. Sex organs.—The sex organs of all the species included in this study aie of the common type found in the Polypodiaceae (Nayar, 1962). Antheridia are often produced by prothalli from early fila mentous stage onwards; vigorously growing thalli produce antheridia only after a broad prolhallial plate is formed. In all the species, some young thalli remain antheridial and with arrested growth, pro ducing antheridia profusely. These may either be branched germ filaments or strap-shaped small thalli at various stages of development, but never cordiUe. The antheridia are small, subglobose or hem i spherical, with an undivided cap cell and short basal cell which is disk shaped in W. accedens and funnel-shaped in the others. Usually only 16-24 spermatozoids are produced per antheridium. At dehiscence the cap cell is bodily thrown off and it collapses in the process. The archegonial neck is short, slender (composed of four rows of cells with 3-4 short cells in a row), and curved away from the apex of the pro- thallus.