. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. 3SO LYCOPODIALES sunken in the soil. The embryo is long dependent for nourishment entirely upon the large prothallus; hence its swollen haustorial foot, which s de- veloped most strongly in the direction of the largest nutritive supply, reacting meanwhile upon the disposition of the other parts of the embryo: in point of origin this is the consequence of unequal turgid distension and division of cells of the foot-tier, which in the Selago-type remain small. The first. Fig. 187. Lycopodium cernuum. You
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. 3SO LYCOPODIALES sunken in the soil. The embryo is long dependent for nourishment entirely upon the large prothallus; hence its swollen haustorial foot, which s de- veloped most strongly in the direction of the largest nutritive supply, reacting meanwhile upon the disposition of the other parts of the embryo: in point of origin this is the consequence of unequal turgid distension and division of cells of the foot-tier, which in the Selago-type remain small. The first. Fig. 187. Lycopodium cernuum. Young embryo emerging from the prothallus. «r=neck of archegonium; s=suspensor; basal wall, corresponding to b, b in Fig. 182, to in Fig. 185, and to in Figs. 183 and 186; <ro/=cotyledon ; /w£=tubercle of protocorm. X 300. (After Treub.) leaves—here an opposite pair, though in other species there is a single cotyledon—are only scale-leaves, which may serve for protection of the apex in forcing its way upwards through the soil; but this is only a derivative function, and it can hardly be doubted, after comparison with the embryo of L. Selago, that the foliage character of the first leaves was the prototype, and that the early formation of colourless scale-leaves in the davatum-annotinum-iy^e is a concomitant of the subterranean habit adopted by their Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bower, F. O. (Frederick Orpen), 1855-1948. London, Macmillan and Co. , Ltd.
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