. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. 54 ALTERNATING GENERATIONS Funaria, Brizi),1 and from various species of Ferns belonging to the Hymenophyllaceae and Polypodiaceae,2 but no examples are on record from the Lycopodiales or Equisetales. Those cells which would in the normal course produce the spores take no part in the formation of the gametophytic growths. In Anthoceros the origin of these is commonly from sub-epidermal cells: in the Mosses from the cells of the seta, or of the sporogonial wall; while in Ferns the archesporial cell if
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. 54 ALTERNATING GENERATIONS Funaria, Brizi),1 and from various species of Ferns belonging to the Hymenophyllaceae and Polypodiaceae,2 but no examples are on record from the Lycopodiales or Equisetales. Those cells which would in the normal course produce the spores take no part in the formation of the gametophytic growths. In Anthoceros the origin of these is commonly from sub-epidermal cells: in the Mosses from the cells of the seta, or of the sporogonial wall; while in Ferns the archesporial cell if already defined in a sporangium is abortive. Thus the aposporous growths are in no sense mere irregularities of development from sporogenous cells. In Anthoceros each growth is apparently referable in origin to a single cell, and the same is probably the case also for Mosses. But in the Ferns this is not so: here the vegetative development may start from a sporangium formed in its normal place: a plurality of the cells of the stalk, or of the sporangial wall surround- ing the abortive central cell may divide, and assume pro- thalloid characters (Fig. 37), or the growth may arise from the receptacle of the sorus (Fig. 37 e) : or again, it may be initiated at some point on the leaf, usually marginal, which thus extends directly into the prothallial expansion, and may bear antheridia and archegonia (Fig. 37 b, c, d). The matter may be further complicated by the combination of apogamy and apospory in the same individual, and this condition has been seen in about half the recorded cases of these abnormalities in Ferns. The apogamous seedlings of Nephrodium pseudo-mas, var. cristata (Cropper), not only sprang themselves in an apogamous manner from the prothallij but proceeded almost at once to an aposporous production of new prothalli on the margins of the young These prothalli bore antheridia,. Fig. 36. Scolopendrium vulgare. Group of sporangia (sp) on a projection, the str
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