iLLINOIS NATURAL HISTORY SURVEY MANUAL 1 
POLLINATION 
Pollination is the transfer of pollen grains from anther to 
stigma. It must take place before fertilization and the production 
of seeds can proceed. In most flowers it seems to be advantageous 
to have the pollen come from some other plant of the same 
species, rather than from the anthers of the same flower. This 
cross-pollination is necessarily brought about by some external 
agency. The principal agents of pollination are wind, water 
and animals. 
Agents of pollination.—Although the simplest form of polli- 
nation is by wind, the structural adaptation of some flowers 
to it is as perfect as that of others to pollination by animals. 
Wind-pollinated flowers are in many cases imperfect—some 
flowers of a species having only stamens and the others only 
pistils. The staminate flowers are often in catkins, which hang 
downward and yield pollen, when it is ready, to the slightest 
breeze. When not in catkins they often have exserted stamens, 
with anthers freely exposed to the wind. Sometimes the pistillate 
flowers are also in catkins, but more frequently they are not. 
Most wind-pollinated flowers produce an abundance of 
pollen, which is necessary because the wind is a very wasteful 
agent. It scatters pollen indiscriminately, so that only a small 
percentage of it falls upon stigmas of the same kind of flowers. 
Upon flowers of different kinds of plants, the pollen ordinarily 
does not germinate, or start to grow. Also, wind-pollinated flow- 
ers usually have neither odor nor nectar, and as a rule are not 
showy. Where they are perfect, stamens and pistils mature at 
separate times, preventing se/f-pollination. 
_ Water is a considerably less important agent, and probably 
none of the flowers in this book depend on it, except bur sedge 
and the water purslane. 
The great majority of flowers described in this book are 
pollinated by insects. Insects visit the flower to obtain food, 
either nectar or pollen, and while getting it incidentally bring 
about pollination. All the many beautiful types of flowers are 
thought to have originated because of this relationship to in- 
sects, a phenomenon which if it were not so common would 
certainly be considered among the most amazing in the whole 
realm of nature. Many flowers are not pollinated at all un- 
less they are visited by insects, and some only if visited by a 
particular kind of insect. 
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