Nature and development of plants . the microspores; mg, megasporangiumcontaining a single spore mother cell, mc. Two integuments, i, are grow-ing up about the sporangium. B, later stage of development, the mega-sporangium, mg, becoming inverted and completely covered by the integu-ment. The mother cell of A has found four daughter cells in series andnot in tetrads as in the Pteridophyta. The innermost cell of the series,ms, only matures as a megaspore; m, micropyle; /, stalk or funiculus ofsporangium. gium, also called the nucellus, its nucleus divides and the daugh-ter nuclei move to each end
Nature and development of plants . the microspores; mg, megasporangiumcontaining a single spore mother cell, mc. Two integuments, i, are grow-ing up about the sporangium. B, later stage of development, the mega-sporangium, mg, becoming inverted and completely covered by the integu-ment. The mother cell of A has found four daughter cells in series andnot in tetrads as in the Pteridophyta. The innermost cell of the series,ms, only matures as a megaspore; m, micropyle; /, stalk or funiculus ofsporangium. gium, also called the nucellus, its nucleus divides and the daugh-ter nuclei move to each end of the spore (Fig. 270, A). Eachof these nuclei divides twice, forming four nuclei at either endof the spore (Fig. 270, B, C). A nucleus from each of these DEVELOPMENT OF PLAXTS 357 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 femalegametophyte. The three outer or micropylar cells are not pro-. Fig. 270. Germination of the megaspore: A, first division of the mega-spore. B, second division of the nuclei. C, final division of the nuclei. vided with walls and consist of a rather lower-lying gamete andtwo nourishing cells, the synergids or helpers (Fig. 271). Theinner group or antipodal cells usually have walls and they areeither soon disorganized and absorbed by the enlarging gameto-phyte or they may remain as permanent features of the gametophytefor a long time and even increase greatly in number, serving tonourish the gametophyte by absorbing food from the endosperm nucleus plays a very important role in the devel-opment of the sporophyte, for as soon as fertilization has beeneffected it forms by repeated division a mass of cells that com-pletely fill the entire space within the enlarging spore, thus pro-viding food for the nourishment of the sporophyte. It wouldappear impossible to compare the various cells of this peculiargam
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