176 



MORPHOLOGY OF THE ANGIOSPERMS 



sharply off from the cytoplasm of the vegetative cell in which it is 

 embedded. 



The formation of the generative cell takes place during late stages in 

 anther development. In a sporangium, the divisions in the development 



Fig. 71. Microsporogenesis and development of the male gametophyte in Porttilaca 

 oleracea. A, row of spore mother cells in anther sac; B, C, meiotic divisions in spore 

 mother cell; D, tetrad of spores nearly mature; E, detail of spore-wall formation in 

 tetrad; F, mature spore, enlarged before germination; G, H, generative and tube cells 

 within spore wall; /, ], mature pollen grain with generative cell and two sperms; K, 

 germinating pollen grain; L, part of pollen tube showing tube nucleus and sperms. 

 {After D. C. Cooper.) 



of the gametophyte are not as nearly simultaneous as are the meiotic 

 divisions, but are not far apart, except in long anthers, such as those of 

 Liriodendron, where there is acropetal succession in germination of the 

 spores. In tetrads that remain permanently together, and in pollinia, the 

 divisions may be simultaneous. 



