SELECTION OF POLLEN 67 



146. It undoubtedly often occurs that various kinds of pollen 

 fall on the same stigma. This is quite likely to be the case 

 with anemophilous pollen, but occurs less frequently in ento- 

 mophilous flowers because many species of insects confine their 

 attention to one or a few species of flowers; and also many 

 species of flowers are visited by only one or a few species of 

 insects. 



147. When pollen from a distantly related plant falls on the 

 stigma of a flower no fertilization occurs. If the pollen comes 

 from a nearly allied plant, however, fertilization mav take 

 place and the resulting offspring will be a hybrid. But normally 

 only pollen coming from a flower of the same species is effica- 

 cious in producing fertilization. If several kinds of pollen fall 

 on the same stigma at about the same time there may, therefore, 

 be a selection of the kind proper to the plant. As between 

 pollen from the same flower and pollen from another flower of 

 the same species it is quite probable that there may, also, be 

 a selection in favor of that yielding cross-fertilization. This is 

 known to be the case in certain plants and, by analogy, it may 

 occur in others. 



The Seed 



148. Fertilization accomplished, the development of the seed 

 begins. The embryo itself is developed from the germ nucleus 

 which results from the fusion of the fertilizing pollen nucleus 

 and the ^g% nucleus of the ovule. But the germ nucleus is 

 only a small part of the ovule. The other parts also grow as 

 the embryo develops, and form the masses of reserve food and 

 the seed coats. 



The Fruit 



149. While the ovules in the ovary are developing into seeds, 

 changes are also taking place in adjacent parts of the flower 

 — changes which would not occur if the ovules failed of 



