SPERAIiVTOPHYTES 



199 



archegonium develops at the micropylar surface 

 of thegametophyte,theneighboringcellscontinue 

 growth, and the archegonium is left in a depres- 

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

 Male gametophyte. — The male gametophyles 

 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 

 shedding of the pollen grain, which is therefore 

 seen to contain three nuclei : those of the per- 

 sistent vegetative cell, of the generative cell, 

 and of the tube cell (fig. 449). 



Fig. 44S. — Diagram of 

 embryo sac (containing fe- 

 male gametophyte) of Dioon, 

 showing two archegonia and 

 the archegonial chamber. — 

 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 

 thru-sting 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 of a 

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

 455, 456, after Coulter. 



