In some species stamens and pistils are so placed In many plants the stamens and pistils are borne on 

 that the pollen cannot get to the stigma, as in different flowers, as in pumpkin end in 



In some species of plants the staminate flowers are In some species the flowers are in two or three 

 borne on one individual and the pistillate flowers forms, with the anthers in one matching the relative 

 on another, as in position of the stigmas in another, and pollen acts 



only on stigmas of corresponding height, as in 





Purple loosestiife 



Primrose 



In some species of plants, if the pollen gets to the stigma of the same flower, 

 it will not lead to fertilization. The pollen will in some cases result in poorer 

 seeds than those produced by means of pollen taken from another flower. But 

 in buckwheat, in most orchids, in certain species of day Hly, and in some 

 members of the bean family the pollen will not even put out a tube if placed 

 on the stigma of the same flower. 



Cross-poUenation Plants that cannot pollenate themselves depend upon 

 outside moving bodies to transfer the pollen for them. The most common 

 moving agency is the wind. That the wind is an effecti\'e agent in pollenation 

 is seen in the amount of pollen present in the dust at certain seasons of the year 

 (see illustration, p. 408). Corn, wheat, oats, grasses generally, many of the 

 common trees, as well as many other plants, depend entirely upon the wind 

 for their pollenation. Another effective agent in distributing pollen for plants 

 is moving water. This is illustrated by the tape-grass, or eel-grass {Vallisneria), 

 which lives near the edges of ponds. The pistillate individuals of the eel- 

 grass grow up to the surface of the water, where the flowers open. The 

 staminate individuals remain below; the closed flowers become detached 



407 



