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 ot 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 ot 

 pollen, which is necessary because the wind is a very wastetul 

 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 diff"erent 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 self-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 it visited by a 

 particular kind of insect. 



18 



