PLANT REPRODUCTION 93 



and gives rise to an embryo or new plant enclosed within a seed. 

 Therefore it will be readilj seen that the embryo is formed within 

 ajid is the essential part of the seed. 



Pollination. — The transfer of the pollen from the stamen to 

 the stigma of the pistil is called pollination. If the pollen is 

 transferred to the stigma of the same flower, it is self-pollina- 

 tion; if to the stigma of another flower on the same plant, it is 

 close pollination; and if to the stigma of a flower on another 

 plant, it is cross-pollination. In some flowers self-pollination is 

 absolutely necessary, because the flower buds never open, while 

 in others it is impossible, because the staminate and pistillate 

 flowers are ou different plants. However, the study of a large 

 number of plants indicates that self-pollination is rare and that 

 close and cross-pollination are very general. 



Methods of Pollination. — There are several methods of pol- 

 lination in the plant kingdom. They are the (1) cleistogamous, 

 in which the bud never opens, as in the case of some violets; 

 therefore, self-pollination; (2) anemophilous, in which the 

 pollen is carried by insects, as in the case of most flowering 

 plants. The insects are probably attracted to the nectar, which 

 is secreted by special glands, or by the odor or possibly by the 

 bright colors. The peculiar forms of the corolla axe frequently 

 associated with some particular species of insects. In some spe- 

 cies this is so pronounced that the plant is dependent on a single 

 species of insects for pollination and cannot produce seeds unless 

 this particular species of insect is present. In addition to these 

 methods, birds are sometimes carriers of pollen, and in some 

 very few cases the pollen is carried by water. However, the 

 fact that many plants live in the water does not indicate that the 

 pollen is carried by water; in most water plants the flower is 



