FLOWERS AND THEIR USES 



279 



the flowers of other plants have low stamens (of about the 

 height of the pistils of the first plant) and high pistils. An 

 insect that visits a flower of the first kind receives pollen on 

 the part of its body that touches an anther ; when it visits 

 a flower of the second kind, the part of its body that touched 

 the anther of the first flower touches the stigma of the 

 second and deposits pollen upon it. Another part of the 

 insect's body touches the anther of the second flower, and 

 when it visits a flower of the first 

 kind it is that part of the body which 

 touches the stigma. 



Some plants even have stamens 

 and pisfils of three different lengths, 

 and consequently three different kinds 

 of flowers. There is still another way 

 in which cross-pollination is some- 

 times favored. The pollen of some 

 plants will not germinate on the 

 stigma of the flower which produced 

 it, nor even on the stigma of another 

 flower of the same plant. In other 

 cases, a pollen grain may germinate on the stigma of the 

 same flower, but the pollen tube does not grow so rapidly 

 nor become so long as it would if the pollen came from 

 another flower, especially a flower borne on another plant. 

 This is the condition in the rye, the pear, the carnation, and 

 the American chestnut. In such cases, no seeds, or but 

 few seeds, result from self-pollination, but many seeds are 

 formed if cross-pollination occurs. 



In other plants, however, pollen from the same flower is 

 as effective, so far as seed production goes, as pollen from 

 a different flower. This is true of oats, beans, peas, and 

 many varieties of wheat. But although many seeds may re- 

 sult from self-pollination in these cases, it does not always 

 follow that the" plants that grow from these seeds will be as 



A B 



Fig. 164. — ■ Primrose 

 flowers : A, one with low 

 stamens and high pistU; 

 B, one with high stamens 

 and low pistil. After 

 Eichler and Prantl. 



