Pteridophyta : Filicineae : Leptosporangiatae-Homosporeae. II. 



ASPIDIUM FILIX-MAS {Nephrodium) 'Male-Fern': Indigenous fern- 

 type of damp under-wood ; massive rhizome obliquely erected, or prostrate at surface- 

 level, with crown of bipinnate Foliage-leaves each season, 3-4 ft. or more long, 

 8-13, in spiral series (3 : 5); primary pinnules 40-50 each side of main rachis, 6 in. 

 long, diminishing distally; secondary pinnules 20-30, half an inch long, diminishing 

 distally, decurrent below and serrated. Sporangia borne in sori on lower surface of 

 pinnules (June), in rows of 4-5 on either side of midrib, fewer distally on all ramifica- 

 tions. Sorus with kidney-shaped, umbrella-like indusium, 2 mm. diam., covering 

 sporangia when young: sporangia 100 or more, formed indefinitely from placental 

 cushion-growth, supplied by end of v.b. 



Sporangia, ovoid, compressed, 250-275 /x long, on slender stalks (-^ mm.) 

 •of 3 rows of cells : wall of one layer; annulus-crest for ^ of periphery, of 15-18 cells 

 with U-thickening (10 /a), coloured golden-brown when adult; 'lip-cells', and 

 dehiscence-mechanism of living cells : archesporium, tapetal layers (2 deep), spore- 

 mother celLs, tetrads (16 X4 = 64); average production dependent on nutrition (48). 

 Spores with brown cuticularized exospore, 50 /x diam., kidney-shaped, with granu- 

 lated surface. Output, at a moderate estimate (10 fronds, 50 pinnules, 30 secondary, 

 10 sori, 100 sporangia, 48 spores) =720 million (possibly 1,000 in a fine plant) per 

 annum. 



Prothallus (= Gametophyte) : Germination of spore to cell-filament with 

 chloroplasts ; broadening to bilateral lamina, i cell thick, to adult-form (3-5 mm.), 

 heart-shaped, with growing-point of small cells in ' notch ' ; median cushion, D.V. 

 organization, rhizoids and reproductive organs on lower surface. Aniheridia 

 scattered, sub-globular outgrowths (50 /x diam.); wall of 2 ring-cells, lid-cell, and 

 central spermatocyte tissue : antherozoids about 16, liberated as motile zoids, spiral of 

 2-3 coils, flagellae on anterior half, multiciliate ; about 30 /x long when straightened 

 out. Chemotactic attraction (malic acid) and fertilization. Archegonia, few, short- 

 lived, continuously produced behind notch, on central many-layered cushion only 

 (10-100), until fertilization is effected for one; half-sunk, venter ill-defined, neck of 

 4 rows, 4-5 cells (100 /x); dehiscence by 4 lip-cells; central series of neck-cell 

 (coenocytic), ventral canal-cell, oosphere (40 /x diam.). Fertilization as fusion of 

 gamete-nuclei only, to diploid zygote (= oospore). 'Germination' immediate; 

 octant-segmentation ; diflferenliation of regions to give the embryonic — 



Sporophyte as a land-organism : emergence of cotyledon (first leaf), with 

 dichotomous ramification, from distended archegonium ; growth of first root ; differ- 

 entiation of shoot-apex, and apical cells; haustorial ' foot '-region, parasitic on 

 enlarged prothallus (10 mm.): independence gained with water-absorption by root: 

 erected axis with 3-sided apical cell ; juvenile leaves with increasing differentiation ; 

 development of bipinnate frond (' megalophylly '). Structure of main axis in terms 

 of dictyostele ; no secondary thickening : development of leaves in phyllotaxis- 

 pattern (3:5) independently of apical cell-segmentation. Root-system wholly 

 adventitious, from massive leaf-bases. No internodal extension in main axis. Leaf- 

 pinnules spaced in leaf-mosaic, as D.V. system; circinnate vernation; leaf-system 

 seasonal, but not 'deciduous': age indefinite; rhizome with occasional branching, 

 giving connected shoots with annual crowns ; but the whole clearly reduced from 

 ■erect tree-fern model (30-60 ft. stem). 



Note, ' Alternation of Generations ', Haploid and Diploid phases, Life-Cycle. 

 L The Sporophyte as land-vegetation, sub-aerial, with intercellular spaces, 

 cuticle, stomata, and transpiration-system; involving vascular supply (xylem), and 

 absorptive root. Production of air-dry, wind-borne spores (hotnosporous), all alike ; 

 wastage-coefficient enormous : chances of germination of spores in hot summer (July) 

 practically 7i{l. Hence restriction to damp situations, as shade-vegetation, and regions 

 with more ample rainfall. 



IL The Gametophyte, a reduced, highly-specialized, and vestigial relic of the 

 aquatic phase (algal and benihic) ; short-lived, precociously reproductive, with no 

 transpiration-mechanism : reproductive organs as much-reduced structures ; output of 

 antherozoids — a few hundred may be sufficient; output of oospheres still smaller: 

 wastage of sexual process extremely small, correlated with small size, and efficiency 



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