of the sexual plant, given casual water-supply by condensation of a saturated 

 atmosphere. 



III. Motile Anther ozoid as retention of flagellated phase of still older plankton- 

 habit. Motility of oosphere lost, consequent on advanced oogamy, and fertilization in 

 situ (no longer discharged). 



Note, no other land-plant so conveniently expresses the independent existence of 

 these 3 phases, as epitomizing and ' recapitulating ' the history of 3 epochs of world- 

 vegetation. Thus the Moss never attains the independence of a land-plant with roots ; 

 Selaginella has lost the free-living (autotrophic) prothallus ; as has also Ginkgo with 

 the culminating tree-habit. 



Pteris Aquilina (Bracken), indigenous and cosmopolitan, more significant as 

 unit of vegetation, clothing hill-sides, in pure association ; also in woodland shade- 

 habit. Highly specialized sporophyte phase : Rhizome, subterranean (for protection), 

 dorsiventral in construction and ramification; 10-20 mm. diam., with internodes 

 elongated (several inches). Foliage-leaves, 2-6 ft., erect, one per shoot-apex, seasonal, 

 with 4-year period. Fronds 3 times pinnated, more or less tripartite ; ultimate lobes 

 coriaceous, with reflexed margins ; hydathode-glands at base of main segments ; vase, 

 system in characteristic D.V. pattern in section. Sporangia along entire course of 

 marginal vein, with membranous indusial overlap of leaf-margin. Details as in 

 Aspidium ; wastage-coefficient at least as large. Prothallus similar : differences only 

 noted in biological adaptations of sporophyte and their consequences : propagation on 

 exposed hill-sides wholly by vegetative growth. 



SELAGINELLA (700). Type of Heterosporous Lycopodineae ; tropical and 

 sub-tropical ; S. spinosa alone indig. : Selaginella inaequalifolia (Hort), Himalya : 

 Shoot-system, sub-erect, 3-4 ft. long, with D.V. frondose habit ; repeatedly divided, 

 in lateral systems, up to 6 in. ; leaves, small, decussate, in 4 rows, as a diagonally 

 orientated, eccentric decussate system ; smaller upper leaves (1 mm.), larger flanking 

 leaves (2 mm.), in symmetrical mosaic (cf. Cupressus). 



Ends of shoots erected, 4-angled and 4-rowed strobili (A in. long), in which 

 sporophylls are differentiated ; majority with microsporangia ; a few, towards base, as 

 megasporangia. Microsporangia in axil of leaf, kidney-shaped, with indefinite tetrads 

 of microspores, 30 /x long, orange-brown ; output 4-5,000 ; Megasporangia, larger 

 (8 mm.), with one tetrad of 4 large white megaspores (300 fx). Ratio of Heterospory, 

 by number, approx. 1,000 : 1 ; by volume, 1 : 1,000. 



Germination of spores independently in casual moisture ; microspores to small 

 prothallus, minute, non-autotrophic, no larger than spore ; producing 4 biflagellated 

 antherozoids only: Megaspore germinating inside ruptured spore-coat, to tissue 

 without chlorophyll, at expense of reserves only, and producing a few archegonia, 

 sunk in tissue at exposed end. Fertilization in casual water-supply ; embryo at first 

 parasitic on food-reserves, with ' suspensor '-mechanism. 



Theory of Megaspore: In the ancestral algal phase of the sea sexual 

 reproduction, by fusion of ' gametes ', was perfected in advancing stages of physiological 

 differentiation from (a) Isogamy (equal gametes), to (ft) a distinction of ' male ' and 

 ' female ' (Heterogamy) ; to (y) one large rounded oosphere (Oogamy), and ultimately 

 this failed to be discharged, and is henceforward (8) ' Fertilized in situ '. 



In emergent Land Flora a very similar progression is presented in the case of 

 wind-borne asexual spores. At first all alike, (a) Homospory (= isospory, Fern) ; then 

 (/?) differentiated, Heterospory (Selaginella), in two sizes, micro- and mega- ; the 

 megaspore becomes reduced to 1 only (y), in turn non-discharged, and hence requiring 

 to be (8) ' pollinated ' in situ. 



The mechanism thus runs closely parallel, but has nothing to do with ' male ' 

 and ' female ' ; sexuality being solely a phenomenon involving a nuclear fusion. Hence 

 flowers, or a plant, bearing microspores, may be termed ' staminate ', but not ' male ', 

 except in a wholly metaphorical or loosely conventional sense, inherited from the time 

 when stamens were thought to be male organs (Linnaeus). Pollination is not 

 fertilization, though it necessarily precedes the latter. The megaspore enclosed in it& 

 megasporangium ultimately initiates the seed-stage (Gymnosperms), and external water 

 ceases to be required for fertilization as the 'plant' attains the full land-habit. 



6 



