Elementary botany . Fig. 387 Section of pistil of tril-lium , showing position ofovules (macrosporangia). Fig. (Podo-phyllum peltatum). GAMETOPHYTE AND SPOROPHYTE. 327 phyllum) and through the ovules when they are quite young, weshall find that the ovule has a structure like that shown in fig. m is a cell much larger than the surrounding ones. This iscalled the macrospore. The tissue surrounding it is called here thenucellus, but because it contains the macrospore it must be themacrosporangium. The two coats or integuments of the ovule areyet short and have not grown out ov
Elementary botany . Fig. 387 Section of pistil of tril-lium , showing position ofovules (macrosporangia). Fig. (Podo-phyllum peltatum). GAMETOPHYTE AND SPOROPHYTE. 327 phyllum) and through the ovules when they are quite young, weshall find that the ovule has a structure like that shown in fig. m is a cell much larger than the surrounding ones. This iscalled the macrospore. The tissue surrounding it is called here thenucellus, but because it contains the macrospore it must be themacrosporangium. The two coats or integuments of the ovule areyet short and have not grown out over the end of the macrospore increases in size, forming first a cavity or sacin the nucellus, the embryo sac. The nucleus divides several. Fig. ovule (macrosporangium) of podophyllum, n, nucellus containing the one-celled stage of the macrospore; , inner integument; , outer integument. times until eight are formed, four in the micropylar end of theembryo sac and four in the opposite end. In some plants ithas been found that one nucleus from each group of four movestoward the middle of the embryo sac. Here they fuse togetherto form one nucleus, the endosperm nucleus or definitive nucleusshown in fig. 390. One of the nuclei at the micropylar end isthe egg, while the two smaller ones nearer the end are the syner- 328 MORPHOLOG Y. gids. The egg cell is all that remains of the archegonium inthis reduced prothallium. The three nuclei at the lower endare the antipodal cells.
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Keywords: ., bookauthoratk, bookcentury1900, bookdecade1900, booksubjectbotany
