THE SPERMATOPHYTES 449 
mother cell is formed. This divides to form four spores but only 
one persists. This is called the megaspore or embryo sac. It 
contains haploid chromosomes. 
DESCRIPTION OF THE GAMETOPHYTE GENERATION 
The Gametophyte generation of the White Pine begins with 
the development of the male and female gametophytes and ter- 
minates with the fertilization of the egg. 
Fic. 337.—Mature carpellate cones of white pine showing separated scales. 
Tue Mate GametopHyTe.—The male gametophyte com- 
mences to form in the mature pollen grain before the pollen is 
shed. A series of three nuclear divisions takes place which cut 
off two small prothallial cells (traces of one of which may be seen 
pushed up against the wall of the fertile cell of the pollen grain), 
a tube nucleus and a generative cell. (See Fig. 338.) At this 
stage the pollen is shed and some of it is carried by air currents 
to the carpellate cones where it sifts in between the ovule-bearing 
scales and accumulates at the scale bases. A number of the 
pollen grains are drawn close to the nucellus of the ovule by the 
drying up of the viscid fluid which fills the pollen chamber. In this 
