138 



FUNDAMENTALS OF CYTOLOGY 



gametes. This division may occur before the anther opens, as in maize, 

 or at some later stage ; hence the pollen grains shed from the anther and 

 transferred to a stigma may contain two or three cells. The further 



Fig. 101. — Microsporogenesis and development of male gametes in purslane (Portulaca) . 

 1, section of anther with microsporocytes; 2, metaphase / in microsporocyte; 3, anaphase 

 //, with spindles at right angles to each other; 4, cytokinesis beginning; 5, detail of develop- 

 ing partition wall; 6, microspore; 7, division of microspore nucleus; 8, generative cell 

 formed; 9, young pollen grain, with tube nucleus and elongate generative cell; 10, generative 

 cell dividing in pollen grain; 11, pollen grain with two male gametes and tube nucleus; 12, 

 male gametes from older pollen grain; 13, germinating pollen grain; tube nucleus entering 

 pollen tube. {After D. C. Cooper.) 



behavior of this small male gametophyte will be described below in the 

 section on syngamy. 



Megasporogenesis and the Female Gametophyte. — The pistil 

 consists typically of an ovary, a more or less elongated style, and a 

 sticky or hairy stigma upon which the pollen will be received. In the 



