. Nature and development of plants. Botany. DEVELOPMENT OF PLANTS 389 ter nuclei move to each end of the spore (Fig. 270, A). Each of these nuclei divides twice, forming four nuclei at either end of the spore (Fig. 270, B, C). This generally completes the nuclear divisions in the gametophyte. Only a few cases are. Fig. 269. Development of the megasporangium and megaspore: A, sec- tional view of the pepper-grass, Lepidium. This flower has two cohering sporophylls, only a portion of the right-hand one being shown, s, stigma with protruding cells to receive the microspores; mg, megasporangium con
. Nature and development of plants. Botany. DEVELOPMENT OF PLANTS 389 ter nuclei move to each end of the spore (Fig. 270, A). Each of these nuclei divides twice, forming four nuclei at either end of the spore (Fig. 270, B, C). This generally completes the nuclear divisions in the gametophyte. Only a few cases are. Fig. 269. Development of the megasporangium and megaspore: A, sec- tional view of the pepper-grass, Lepidium. This flower has two cohering sporophylls, only a portion of the right-hand one being shown, s, stigma with protruding cells to receive the microspores; mg, megasporangium con- taining a single spore mother cell, mc. Two integuments, i, are growing up about the sporangium. B, later stage of development, the megasporangium, mg, becoming inverted and completely covered by the integument. The mother cell of A has formed four daughter cells in series and not in tetrads as in the Pteridophyta. The innermost cell of the series, ms, only matures as a megaspore; m, micropyle;/, stalk or funiculus of sporangium. known where a larger number of nuclei are formed—compare with the gymnosperms. A nucleus from each of these groups, called the polar nuclei, now approach each other and fuse, forming a single large nucleus that is usually called the endo- sperm nucleus. This rudimentary growth represents the female gametophyte. The three outer or micropylar cells are not pro-. 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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