426 PLANTS AND THEIR RELATION TO MAN 



others, like the tomato, contain many seeds. Sometimes the 

 enlarged ovary wall is soft and juicy, as in the cherry ; sometimes 

 it is hard and dry, as in the walnut. 



The pollen travels from flower to flower. Pollen grains 

 which fall on the stigmas of their own flowers develop poor 

 seeds or no seeds at all. Seeds are the offspring of two parents, 

 and in order to obtain seeds of the finest grade, the two parents 

 must belong to different flowers ; that is, the pollen which falls 

 on the stigma of one flower must be pollen from another 

 flower. 



Just as the wind blows dust through the air, it blows pollen. 

 It lifts the light powdery pollen grains from the anthers and 

 carries them until they settle on flowers, on leaves, and on fences. 

 Pollen that settles on leaves and fences is wasted, but pollen 

 which chances to rest on a flower like that from which it came 

 makes its way to the ovules and unites with them to form seeds. 

 But wind does not have access to the pollen of all blossoms. 

 In many flowers the stamens are inclosed by the petals and the 

 wind cannot reach their pollen. This is true of 

 the sweet pea (Fig. 291), where the petals are 

 keel-shaped and shield the stamens. Bees force 

 their way into the closed corolla in search of 

 nectar and rub pollen on their hairy bodies as 

 FlG S weet pea^ tne y brush against the anthers. When the bee 

 rests on another sweet pea, it rubs against the 

 stigma and deposits on it some of the pollen brushed from the 

 first flower. When flowers have sticky or protected pollen, they 

 are entirely dependent upon insects and birds for the transfer 

 of pollen. 



The pollen of the clover plant is distributed by the bees and 

 unless the fragrant blossoms are visited by these busy insects, 

 seeds do not develop. Some years ago the Australians im- 

 ported clover seed and attempted to raise clover as fodder for 



