450 PHARMACEUTICAL BOTANY 
fluid they germinate forming pollen tubes. The transfer of 
pollen grains from the pollen sac to the pollen chamber and 
consequent germination therein is called pollination. The con- 
tents of a mature pollen-grain constitutes the male gametophyte. 
Fic. 338.—Pine Pollen and development of pollen tube. In A the pollen grain. 
is shown Containing prothallial cells (6). They have been cut off before the grain 
was shed. The tube nucleus (7) has been divided off from the generative nucleus 
(G). 
In B the tube has been put forth and the tube nucleus has moved down into it. 
Between the stages represented in B and C the generative nucleus has divided 
to form a stalk nucleus (ST) and a body nucleus (B). 
In C four nuclei are present in the pollen tube,—the tube nucleus (TJ), the stalk 
nucleus (S7), and the two sperm nuclei (S). The sperm nuclei have been pro- 
duced by a division of the body cell, the latter having disappeared. (After Atwood.) 
THE FEMALE GAMETOPHYTE.—If the embryo-sac be examined 
at about the time of pollination, it will be found to consist of a 
single cell containing a single nucleus surrounded by cytoplasm. 
Very shortly afterward, however, the nucleus divides repeatedly 
to form a large number of nuclei which are scattered throughout 
the cytoplasm. Each nucleus accumulates around itself a por- 
eR eRe 
