. Nature and development of plants. Botany. 348 SPOROPHYLLS OF SELAGINELLA and, as has been stated, characterizes some of the fossil Equise- tales. The megaspores are generally formed at the base of the strobilus and the microspores occupy the upper sporangia (Fig. 242). The sporangia are called microsporangia and megaspor- angia accordingly as they contain small or large spores and for the same reason the leaves may be designated as micro- and. 6A Fig. 242. Sporophylls and spores of Selaginella: 2, strobilus with lower sporophylls separated for spore dissemination. 3, megasporophyll with spor
. Nature and development of plants. Botany. 348 SPOROPHYLLS OF SELAGINELLA and, as has been stated, characterizes some of the fossil Equise- tales. The megaspores are generally formed at the base of the strobilus and the microspores occupy the upper sporangia (Fig. 242). The sporangia are called microsporangia and megaspor- angia accordingly as they contain small or large spores and for the same reason the leaves may be designated as micro- and. 6A Fig. 242. Sporophylls and spores of Selaginella: 2, strobilus with lower sporophylls separated for spore dissemination. 3, megasporophyll with sporangium containing four megaspores. 4, microsporophyll. 5, mega- spore enlarged. 6, microspore equally magnified. (>A, more enlarged view of the microspore. The triangular surfaces of the spores show that these spores have been formed in tetrads from a spore mother cell as in previous groups. mega-sporophylls. The two kinds of spores originate in the same manner as previously noted and the difference in size is due to the amount of food which they receive. In the case of the microspores, the numerous mother cells of the sporangia form four spores each in the usual manner: but in the megasporangia only one of the mother cells divides in this manner, and in some cases only one spore is formed. The other mother cells do not develop and are ultimately consumed in nourishing the mega- spores. As a result of the large amount of food transferred to the megasporangium, both it and especially the one to four spores become much larger than the others (Fig. 242, 3-6). The physiological differentiation of the spores noted in Eguisetum. 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 Curtis, Carlton Clarence, 1864-1945. New York, H. Holt
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