SPERMATOPHYTES 



199 



archegonium develops'at the mil ropylar surface 

 of the gametophyte, the neighboring cells continue 



growth, and the archegonium is left in a depres- 

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

 Male gametophyte. — The male gametophytes 

 differ from those of Selaginella and Isoetcs 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. 448. — Diagram of 

 embryo sac (containing fe- 

 male gametophyte) olDioon, 

 showing two archegonia and 

 the archegonial chamber. — 

 After Chamberlain. 



Figs. 449-456. — Male gametophyte of Cycas rcvoluta: 449, shedding stage of micro- 

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

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

 (tube nucleus has passed into the pollen tube); 45 t, 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* a 

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

 455. 45°. after Coulter. 



