THE POLLEN GRAIN AND ITS WORK 41 
sac, egg, and primary endosperm nucleus. Redraw this figure 
on a sheet of paper and label the parts. 
Although pistils vary much in number of carpels, length of 
styles, and in number of Jocules and ovules, there is uniformity 
in organization and adaptation of parts to special functions. 
The stigma is especially adapted for receiving pollen, the style 
supports the stigma in a position suitable for receiving the pollen, 
and the ovary protects the delicate ovules in which is the embryo 
sac containing the egg and primary 
endosperm nucleus, which are the 
chief structures of the pistil. 
The Stamen. — The stamen usu- 
ally consists of two parts; the en- 
larged terminal portion, or anther; 
and the stalk, or filament. The 
filament is often so short as to seem 
to be absent. Point out the parts 
of the stamen in A of Figure 48. 
The anther is usually four lobed rn aoe 
Maca j . ther; f, filament. B, much en- 
and within each lobe is a cavity, larged cross section of an anther, 
called locule, which contains many showing the locules and pollen 
globular bodies known as pollen or grains. The two locules at the 
pollen grains. When the pollen is left have opened, allowing the 
mature, the walls of the anther pollen s0-Staps 
open and allow the pollen to escape. Notice the cross sec- 
tion of an anther shown in B of Figure 48. Point out the 
locules and pollen grains. Notice that two of the locules have 
opened. 
The Pollen Grain and its Work. — The pollen grain is a cell 
with its living matter enclosed in a heavy protective wall. It 
needs to be well protected, for during its journey to the pistil, 
destructive agencies such as cold, heat, and drying are encoun- 
tered. The transference of the pollen to the stigma is called 
pollination. Pollination is a very important event, for the pollen 
cannot perform its function except on the stigma. 
On the stigma the pollen grain grows a tube which traverses 
the stigma and style, pierces the ovule, and reaches the embryo 
sac. Pollen grains, when first formed in the anther, have only 
one nucleus, but in preparation for the work of fertilization, there 
is nuclear division and as a result there are three nuclei in a well 
