. Lectures on the evolution of plants. Botany; Plants. 150 EVOLUTION OF PLANTS filled with accumulated food substances which serve to supply the developing female gametophyte with food, as the latter does not contain chlorophyll. The gam- etophyte, as in Selaginella, is almost entirely included within the large macrospore, and the formation of the. Fig. 39 (Heterosporoas Ferns). — A, sporophyte of Isoetes echinospora; B, a single leaf showing the enlarged base bearing a single macrosporan- gium, ma; the mlcrosporangia are much the same; C, a germinated microspore with the contained gametophyte
. Lectures on the evolution of plants. Botany; Plants. 150 EVOLUTION OF PLANTS filled with accumulated food substances which serve to supply the developing female gametophyte with food, as the latter does not contain chlorophyll. The gam- etophyte, as in Selaginella, is almost entirely included within the large macrospore, and the formation of the. Fig. 39 (Heterosporoas Ferns). — A, sporophyte of Isoetes echinospora; B, a single leaf showing the enlarged base bearing a single macrosporan- gium, ma; the mlcrosporangia are much the same; C, a germinated microspore with the contained gametophyte reduced to a single vegeta^ tive cell, v, and an antheridium with four coiled spermatozoids; D, Marsilia vestita, a heterosporous form allied to the leptosporaugiate ferns; sp, the " sporocarp " or modified leaf-segment within which are borne the sporangia; E, section of the upper part of the macrospore and female gametophyte, here reduced to a single archegonium, ar; the body of the macrospore, sp, remains undivided; F, spermatozoid of Marsilia; z, the remains of the central part of the sperm-cell. cells is preceded by a repeated divisioij of the nuclei as in the formation of the gametophyte or "endosperm" of the flowering plants. Germination, however, does not begin until the spores have been set free. The Jirche-. 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
