PLANT ORGANS AND ORGANISMS 199 



The Stigma. This is usually a viscid papillose surface of greater or 

 less expanse functioning for pollen reception. In wind-pollinated 

 flowers such as the grasses, the stigmas are the numerous feathery 

 hairs which cover the ends of the styles and intended to catch flying 

 pollen grains. In animal-pollinated flowers, the stigmas are usually 

 small restricted knobs, lines or depressions. The stigmatic papillae 

 vary in size in different plants and even may vary on different 

 individuals of the same species. Thus in the long styles of Primula, 

 the stigmatic papillae are elongated columnar hair-like structures, 

 whereas in the short styles of short-styled flowers the papillae are 

 small knob-like cellular swellings. 



POLLINATION 



Pollination is the transfer of pollen from anther to stigma and 

 the consequent germination thereon. It is a necessary step to 

 fertilization. 



When the pollen is transferred to the stigma of its own flower the 

 process is called Close or Self-pollination', if to a stigma of another 

 flower, Cross-pollination. If fertilization follows, these processes are 

 termed respectively, Close or Self-fertilization and Cross-fertilization. 

 Close-fertilization means in time ruination to the race and happily is 

 prevented in many cases by (a) the stamens and pistils standing in 

 extraordinary relation to each other, (b) by the anthers and pistils 

 maturing at different times, (c) by the pollen in many cases germin- 

 ating better on the stigma of another flower than its own. 



The agents which are responsible for cross-pollination are the 

 wind, insects, water currents, small animals, and man. 



Wind-pollinated, flowering plants are called Anemophilous; their 

 pollen is dry and powdery, flowers inconspicuous and inodorous, as 

 in the Pines, Wheat, Walnut, Hop, etc. 



Insect-pollinated plants are called Entomophilous. These, being 

 dependent upon the visits of insects for fertilization, possess bril- 

 liantly colored corollas, have fragrant odors, and secrete nectar, a 

 sweet liquid very attractive to insects, which are adapted to this work 

 through the possession of a pollen-carrying apparatus. Example: 

 Orchids. 



