. Lectures on the evolution of plants. Botany; Plants. SEED PLANTS 163 of the size of a large plum. The very large macrospore (Fig. 40, B, ma) has a definite thick membrane like that of the ferns, hut is retained permanently within the sporan- gium. So far as it is known, the development of the. Fig. 40 (Cycadacese). — A, a sporophyll of Cycas circinalis, with six ovules (maerosporangia), nia; B, longitudinal section of a young ovule of C. revolnta, showing the single large macrospore, ma; C, a sporophyll from the male cone of C. revmuta, showing the lower surface covered with groups or sori o
. Lectures on the evolution of plants. Botany; Plants. SEED PLANTS 163 of the size of a large plum. The very large macrospore (Fig. 40, B, ma) has a definite thick membrane like that of the ferns, hut is retained permanently within the sporan- gium. So far as it is known, the development of the. Fig. 40 (Cycadacese). — A, a sporophyll of Cycas circinalis, with six ovules (maerosporangia), nia; B, longitudinal section of a young ovule of C. revolnta, showing the single large macrospore, ma; C, a sporophyll from the male cone of C. revmuta, showing the lower surface covered with groups or sori of microsporangia, mi; D, a single sorus of five miorosporangia; E, a microspore (pollen-spore), showing the rudimen- tary, antheridium, an; the larger antheridial cell later gives rise to two large spermatozoids; F, a young leaf of C. revoluta, showing the fern-like coiling of the divisions; G, a scale from the female cone of Zainia integrifolia, with two ovules, ma; H, section through the ovule at the time of fertilization; pc, the pollen-chamber with three germi- nating pollen-spores; g, the vegetative tissue of the female gametophyte contained within the macrospore; ar, two arehegonia; I, a spermato- zoid of Zamia, showing the numerous cilia, c. (Figs. H, I, after Webher.) gametophyte is much like that of Isoetes or Selaginella, but the details are still somewhat imperfectly known. The gametophyte, if fertilization is not effected, may grow out beyond the spore and develop 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 Campbell, Douglas Houghton, 1859-1953. New York, London, The Macmillan company
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Keywords: ., bookcentury1900, bookdecade, booksubjectbotany, booksubjectplants
