SPERMATOPHYTES 



199 



archegonium develops at the micropylar surface 

 of the gametophyte, the neighboring cells continue 

 growth, and the archegonium is left in a depres- 

 sion known as the archegonial chamber (fig. 448). 

 Male gametophyte. The male gametophytes 

 differ from those of Selaginella and Isoetes in 

 certain important particulars. The first divi- 

 sion within the microspore (pollen grain) cuts off 

 a persistent vegetative cell. The next division 

 gives rise to the generative cell (primary 

 spermatogenous cell) and the tube cell. This is 



the usual condition of the gametophyte at the 



/ FIG. 448. Diagram of 



shedding of the pollen gram, which is therefore embryo sac (containing fe- 



seen to contain three nuclei: those of the per- male gametophyte) of Dioon, 

 sistent vegetative cell, of the generative cell, 



and of the tube cell (fig. 449). After CHAMBERLAIN. 



FIGS. 449-456. Male gametophyte of Cycas revoluta: 449, shedding stage of micro- 

 spore (pollen grain), showing persistent vegetative cell, generative cell, and tube cell; 

 450, later stage (after shedding), showing rounded -off vegetative and generative cells 

 (tube nucleus has passed into the pollen tube); 451, division of nucleus of generative 

 cell into nuclei of stalk and body cells; 452, enlargement of nucleus of body cell, and 

 thrusting out of the stalk nucleus; 453, division of body cell to form the two sperm 

 mother cells, in each of which a ciliated sperm is beginning to form; 454, section o f a 

 developing sperm; 455, 456, two views of a mature sperm. 449-454, after IKENO, 

 455, 456, after COULTER. 



