DEVELOPMENT OF PLANTS 



373 



125. The Gametophyte of the Angiospermae. — The angio- 

 sperms have developed along quite distinct Hnes, but they show 

 such a remarkable uniformity in the development and character 

 of the gametophyte generation that this feature of their life his- 



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; rng, 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. 



tory may be considered at this point as it applies to all forms. 

 The megasporangium, also called the ovule, originates in the 

 cavity of the ovary at various points known as the placenta (Fig. 

 269, A). The structure of the sporangium and the formation 

 of the megaspore is very similar to that of the gymnosperms. 

 More often two integuments are formed and the sporangium or 



