. A textbook of botany for colleges and universities ... Botany. 140 MORPHOLOGY. cells contribute to the nutrition of 40-75 mother cells that function. These mother cells become relatively very large and produce large spores, the total output of megaspores being 150-300 (fig. 317). Both kinds of spores escape by the decay of the sporangium wall. Male gametophyte.—The male gametophyte is still more simple than that of Selaginella (figs. 318-320). It consists of a single vegetative cell and a single antheridium, as in Selaginella; but the sperm mother cells are only four in number. This is the l
. A textbook of botany for colleges and universities ... Botany. 140 MORPHOLOGY. cells contribute to the nutrition of 40-75 mother cells that function. These mother cells become relatively very large and produce large spores, the total output of megaspores being 150-300 (fig. 317). Both kinds of spores escape by the decay of the sporangium wall. Male gametophyte.—The male gametophyte is still more simple than that of Selaginella (figs. 318-320). It consists of a single vegetative cell and a single antheridium, as in Selaginella; but the sperm mother cells are only four in number. This is the lowest number reached among pteridophytes, and the nearest approach to seed plants, among which the sperm mother cells are reduced to two. The sperms are large, spirally coiled, and multiciliate (fig. 320), such as characterize all other pteridophytes ex- taining a sperm) are free cept Lycopodiales. It in the antheridial cavity; js this feature of IsoeteS 320, sperm. — After Bela- f ———~-^ ___ ,j.^ that perhaps presents the greatest obstacle to including it among Lycopodiales. Feioaie gametophyte.—The female gameto- phyte develops in the same general way as does Figs. 318-320. — Male gametophyte of Isoetes: 318, stage showing the vegetative cell (at bottom and without nucleus) and the antheridium (with three wall cells visible and the central primary sper- matogenous cell); 319, older stage, in which the wall cells have broken down and the four mother cells (each con-. 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 Coulter, John Merle, 1851-1928; Barnes, Charles Reid, 1858-1910, joint author; Cowles, Henry Chandler, 1869- joint author. New York, Cincinnati [etc] American book company
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