Nature and development of plants . o adaptedto the present conditions upon earth. 125. The Gametophyte of the Angiospermae.—The angio-sperms have developed along quite distinct lines, but they showsuch a remarkable uniformity in the development and characterof the gametophyte generation that this feature of their life his-tory may be considered at this point as it applies to all megasporangium, also called the ovule, originates in thecavity of the ovary at various points known as the placenta (, A). The structure of the sporangium and the formationof the megaspore is very simi


Nature and development of plants . o adaptedto the present conditions upon earth. 125. The Gametophyte of the Angiospermae.—The angio-sperms have developed along quite distinct lines, but they showsuch a remarkable uniformity in the development and characterof the gametophyte generation that this feature of their life his-tory may be considered at this point as it applies to all megasporangium, also called the ovule, originates in thecavity of the ovary at various points known as the placenta (, A). The structure of the sporangium and the formationof the megaspore is very similar to that of the often two integuments are formed and the sporangium orthe stalk which supports it becomes curved so that it very fre- 356 GAMETOPHYTE OF ANGIOSPEKMS quently is turned completely over (Fig. 269, B). The germina-tion of the megaspore results in a female gametophyte which isvery much more reduced than in the case of the the megaspore enlarges, disorganizing the cells of the sporan-. Fig. 269. Development of the megasporangium and megaspore: A, sec-tional view of the pepper-grass, Lcpidium. This flower has two coheringsporophylls, only a portion of the right-hand one being shown, s, stigmawith protruding cells to receive 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


Size: 1764px × 1416px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No

Keywords: ., bookcentury1900, bookdecade1900, bookpublisher, booksubjectplants