SPERMATOPHYTES 
199 
archegonium develops at the micropylar surface 
of the gametophyte, the neighboring cellscontinue 
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 ,, 
J FIG. 448. Diagram of 
shedding of the pollen grain, which is therefore embryo sac (containing fc- 
seen to contain three nuclei : those of the per- male gametophyte) of Dioon, 
,. n f ,1 ,. n showing two archegonia and 
sistent vegetative cell, of the generative cell, t 
' the archegonial chamber. 
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* a 
developing sperm; 455, 456, two views of a mature sperm. 449454, after IKENO, 
455, 456, after COULTER. 
