28 
PHARMACEUTICAL BOTANY 
except at the apex where an opening, the micropyle is evident. The 
micropyle is the gateway to the pollen chamber which lies below it. 
Within the nucellus occurs a megaspore or embryo sac. 
DESCRIPTION OF THE GAMETOPHYTE GENERATION 
The Gametophyte generation of the White Pine begins with the 
development of the male and female gametophytes and terminates 
with the fertilization of the egg. 
The Male Gametophyte. — The male gametophyte commences 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 prothal- 
lial 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. At this stage the pollen is shed and some of it is 
Fig. io. — The white pine (Pinus Strobus). Sections through mature pollen 
grains; at the left the remnants of two prothallial cells can be seen, while at the 
right all signs of the first cell have disappeared. Pollen collected June 9, 1898. 
X about 600. (Gager, after Margaret C. Ferguson.) 
carried by air currents to the carpellate cones where it sifts in be- 
tween the ovule-bearing scales and accumulates at the scale bases. 
This is pollination. 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 fluid they germinate form- 
ing pollen tubes. The transfer of pollen grains from the pollen sac 
to the pollen chamber and consequent germination therein is called 
pollination. 
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 
