. Botany of the living plant. Botany; Plants. LYCOPODIALES 517 The sporangium arises in the axil of the Bporophyll, just within the lignle. After the first segmentations arc past it is found to consi I I a short tl stalk, bearing the slightly flattened sporangial head. This contain up of sporogenous cells, from which later a surrounding tapetal lay< I is ( ut off. Outside this is a wall composed of two layers of colls (Fig. .)<".. /.,. Later the spore-mother-cells round themselves off, becoming isolated in .1 liquid that fills the enlarging cavity. Up to this point it is impossible
. Botany of the living plant. Botany; Plants. LYCOPODIALES 517 The sporangium arises in the axil of the Bporophyll, just within the lignle. After the first segmentations arc past it is found to consi I I a short tl stalk, bearing the slightly flattened sporangial head. This contain up of sporogenous cells, from which later a surrounding tapetal lay< I is ( ut off. Outside this is a wall composed of two layers of colls (Fig. .)<".. /.,. Later the spore-mother-cells round themselves off, becoming isolated in .1 liquid that fills the enlarging cavity. Up to this point it is impossible to tell which type of spore the sporangium will produce. This fact indicates that the megasporangium and microsporangium are differentiated from one original type. In the case of a microsporangium all the spore- mother-cells undergo the tetrad division, and a large number of microspores is the result. But if it is to be a megasporangium, only one (in some species two) of the spore-mother-cells develops further (Fig. 410), the rest becoming disorganised. The four megaspores, with rugged walls, occupy the whole sporangium at maturity (Fig. 408).. Fig. 410. Selaginella spinulosa. Section of megasporangium, showinc: the single fertile tetrad still very small, and the rest ot the sporogenous cells arrested. ( x 100.) F. O. B. The germination of both types of spores may begin before they are shed, but it is continued on the moist soil. The microspore first partitions off a lenti- cular cell, which, as it appears to perform no function, and does not develop further, may be held as vestigial, representing the vegetative region of a male prothallus. The rest of the contents segment to. 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; Wardlaw, C. W. (Claude Wilson), 1901-. Lon
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Keywords: ., bookcentury1900, bookpublis, booksubjectbotany, booksubjectplants
