SUMMARY Morphology of the spores, prothalli and juvenile leaves of 6 spp. of Pellaea. and 2 spp. of Notholaena is described. The spores are trilete and possess a crassimarginate laesura. The exine is psilate and there is a distinct psilate perine in Notholaena. In most species of Pellaea the exine is psilate, but there is a perinous ornamented outer layer closely adhering to it: the exine is spinulose and a perinous layer is absent in P. falcata and P. rotundifolia. The germ filament is composed of short, thick cells. A prothallial plate is formed by longitudinal divisions of the anterior cells when the germ filaments are 4–10 cells long. In some species, the terminal cells of the filament are sluggish and are often pushed aside by expansion of cells behind them. Young prothalli are usually ameristic but a sluggish obconical apical cell may be differentiated in some species. As the prothallus grows, the apex becomes notched and cordate. Cells behind the apical notch then constitute an apical meristem. Formation of a midrib is initiated when the prothalli are 5–6 weeks old. P. doniana, P. falcata and P. rotundifolia are sexually reproducing species and develop cordate naked prothalli with thin midribs bearing sex organs. The others are apogamous and the prothalli, soon after the development of a cordate apex, become irregular in shape. Apogamous development of the sporophyte is initiated by the formation of a multicellular cushion on the lower surface of the thallus, generally behind the apical notch: on highly lobed thalli the major lobes may develop a separate sporophyte on each. The cushion develops glandular hairs and paleae similar to those on the sporophyte and grows out as a flat, hood‐like protuberance in which a 3 ‐sided meristematic cell may soon be developed. The hood grows out as the 1st juvenile leaf and often a second leaf is soon developed near its base. A stem apex is differentiated by cells close to the leaf base and further leaves are formed. No roots are produced till the sporophyte develops 3 or 4 leaves. Vascular elements are developed in the apogamous cushion early in development and often extend into the prothallial tissue below. The lamina of the early juvenile leaves is nearly spatulate and entire or faintly lobed: it is naked in the first few leaves, but later, glandular hairs spread from the stipe upwards over the lamina.

SUMMARY Morphology of the spores, prothalli and juvenile sporophytes of 6 spp. of Blechnum, 4 spp. oi Doodia, 3 spp. of Woodwardia and 2 spp. of Stenochlaena is described. The spores are monolete, bilateral, with tenuimarginate laesura, and ranging in size from 30–35 times 45–55 μ in Doodia to 40–50 times 70–75 μ in Woodwardia. The exine is 2–3 μ thick and smooth, except in Stenochlaena in which it is prominently verrucate to rugulose. All genera, except Stenochlaena, are perinate, the perine being granulose and either loose and wrinkled as in Woodwardia or closely adherent to the exine and devoid of wrinkles as in Doodia. The spores germinate within 2–3 days of sowing and develop within 3 or 4 days of germination into densely chlorophyllous germ filaments, 3–9 cells long. The rhizoids are light brownish in colour and may include a few scattered plastids. There is some variation in the sequence of cell divisions during the development of a prothallial plate and establishment of a meristem, the same species often exhibiting a fair amount of plasticity in developmental history. The simplest condition is one in which the anterior cells of the germ filament, including the terminal cell, divide longitudinally and an obconical meri‐stematic cell is differentiated by an oblique division in one of the daughter cells of the terminal cell (as in B. gibbum, B. orientate, D. dives and often in D. maxima). The prothallial plate then expands and develops a cordate apex; the meristematic cell is later replaced by a multicellular meristem in the usual way. In most spp. of Blechnum, however, the terminal cell of the germ filament produces an apical hair before dividing longitudinally. Also, a meristematic cell may not be differentiated soon after the first longitudinal division, one of the daughter cells continuing growth of the germ filament. In Woodwardia spp., D. aspera and D. media the terminal cell (sometimes 2 cells at the anterior end) becomes quiescent when the germ filaments are 5–8 cells long. The cell behind i t divides longitudinally and one of the daughter cells develops an obconical meristematic cell adjacent to the quiescent apex, as in the Doodia spp., or by further divisions form an asymmetric, broad, prothallial plate in which a meristematic cell is differentiated in a marginal cell on the broader side of the plate. A marginal hair is produced prior to the establishment of a meristematic cell. The meristematic region later becomes ‘apical’ by unilateral growth of the young prothallus. In Stenochlaena there is a perceptible retardation in growth at the anterior end of the germ filaments when they are 6 7 cells long; the terminal cell often ends in a hair and a prothallial plate is developed from cells behind the quiescent apical region of the germ filament. The meristematic cell is developed laterally. The mature prothallus is of the cordate type, reaching maturity in about 8 weeks from spore germination, but often continuing growth for long and sometimes elongating markedly with age. In Stenochluena the prothall...

No abstract

The rhizome of Okandru pistillaris and 0. wdlichii is elongated (erect in the former, creeping in the latter), cylindrical, clothed with peltate, non-glandular, hairy palem and bearing leaves in small clusters separated by long leafless portions. The ground tissue of the rhizome is composed of thick-walled parenchyma, and there is a peripheral sclerenchymatous sheath as well as a few scattered slender sclerenchyma strands in the pith close to the vascular cylinder. The vascular cylinder is dissected into a loose reticulum of slender meristeles by crowded, spirally arranged leaf gaps. I n the 'leafless' portions of the rhizome these leaf gaps are associated with a solitary vestigial leaf trace : where well-developed leaves occur, each gap is associated with two or three leaf trace bundles. In 0. pistillark, well developed leaves are in whorls at regular intervals; in 0. wallichii they are in small well-separated groups, each group consisting of two to six leaves in two irregular rows on the dorsal surface (i.e. leaves all dong the ventral surface are suppressed). Leaves in both the species are simple with an entire, freeveined lamina and with an articulated stipe, the articulation being towards (but not at) the base and formed of an abscission pad. Branches of the rhizome are borne in pairs and each branch trace is a solitary cylindrical vascular strand, unaccompanied by any branch gap in the stelar cylinder. Sporangia are in circular sori placed in a row close to the midrib and protected by reniform indusia. The sporangial stalk bears glandular hairs, and is two cells thick except at the capsule base, where a short third row is developed secondarily during sporangial development as a protrusion from a lateral wall cell of the capsule base. The spores are of the bilateral type provided with a loose wrinkled perine : spinose excrescences occur over the exine aa well as the perine. The prothallus is of the cordate type, bearing unicellular papillate hairs profusely on the surfaces and margin. It develops from a uniseriate germ-filament which develops into a prothallial plate by longitudinal divisions in the anterior cells. The terminal cell of the germ filament ends in a hair either prior to or immediately after the initiation of plate formation.

No abstract