REPRODUCTION 237 



produced varied more than those which came from self 

 pollinated seeds. 



In many plants, however, self pollination occurs. 

 Sometimes this is accidental, but in many flowers self 

 pollination is apparently definitely provided for. The 

 positions of the anthers and the stigmas are often such 

 that some of the pollen must fall directly upon the 

 stigma. Some plants, like the closed gentian, produce 

 flowers which never open and are thus necessarily 

 self-pollinated. Cross pollination is the more common 

 method, and there are various devices for securing it. 

 In some species of plants the flowers do not have both 

 ovaries and stamens. The flowers on some plants have 

 only ovaries, while those on other plants of the same 

 species have only stamens. In other species the stamens 

 and ovaries of the same flower do not mature at the 

 same time. Cross pollination is usually secured through 

 one of two agencies, the wind or insects. Flowers which 

 depend upon insects for cross fertilization are made 

 attractive. Their showy color, their odor, and the 

 nectar which they contain, all serve as attractive fea- 

 tures for insects. The pollen is used by many for food. 

 Xectar is also used for food and out of it the bee makes 

 honey. Flowers are visited by a great many kinds of 

 insects. Those which are most useful for transferring 

 pollen have bodies covered with hairs to which the 

 pollen easily adheres. In the bee a certain part of the 

 hind leg is covered with stiff hairs forming a "pollen 

 basket." The bee collects pollen for food, but while 



