210 THE LIFE OF FLOWERING PLANTS 
Cross-Pollination. — Reference has been made to the 
fact that pollen is necessary for the formation of seeds, and that 
in most cases it is the 
pollen of some other plant 
of the same kind that is 
used. When the pollen 
of one flower is trans¬ 
ferred to the stigma of 
another of the same kind, 
the process is known as 
cross-pollination. On the 
other hand, when a stigma 
gets pollen from the sta¬ 
mens of its own flowers it 
is said to be self-polli¬ 
nated. The distribution 
of pollen is accomplished 
by insects and by wind more than by other agents. Pollen 
that is to be scattered by wind has two adaptations: (1) it 
is very abundant, for much of it is 
light, that it may be easily carried. 
The pollen of pines which is so 
abundant as to cause the so-called 
“sulphur showers” in the spring 
illustrates this, and the pollen of 
grasses which is extremely light 
illustrates the other fact. Plants 
that are wind-pollinated usually 
lack odor and color and floral en¬ 
velopes (accessory parts), but they 
have adaptations in the stigmas, 
which are either plumy or feathery 
or broad and sticky, the better to 
catch and hold the pollen grains 
brought to them by the wind. 
sure to be lost; (2) it is 
Figure 195.— Pollen Grain 
Sprouted. 
The upper nuclei are male or 
generative nuclei. * 
Figure 194. — Salvia. 
A , stamens mature ; B, pistil mature; 
C, flower after pollination. 
