46 



FLOWERS AND THEIR WORK 



tance. It is only in recent years that the fruit growers of Cali- 

 fornia have discovered that the fertihzation of the female flowers 

 is brought about by a gallfly which bores into the young fruit. "^ 

 The last two cases are only some of the many examples of mutual 

 help among plants and animals. 



Pollination by the Wind. — Not all flowers are dependent upon 

 insects for cross-pollination. Many of the earliest of spring flowers 

 appear almost before the insects do. These flowers, needing no 

 conspicuous colors or showj^ corolla to attract insects, often lack 



this part altogether. 

 In fact, we are apt en- 

 tirely to overlook the 

 flowers which appear 

 in the spring upon 

 our common forest 

 and shade trees. In 

 many trees the flowers 

 appear before the 

 leaves come out. Such 

 flowers are dependent 

 upon the wind to 

 carry pollen from the 

 stamens of one flower 

 to the pistil of an- 

 other. Most of our 

 common trees, oak, 

 poplar, maple, and 

 others, are cross-pol- 

 linated almost entirely 

 by the wind. 



Among the adapta- 

 tions that a wind-pollinated flower shows are : (1) The develop- 

 ment of very many pollen grains to each ovule. In one of 

 the insect-pollinated flowers, that of the night-blooming cereus, 

 the ratio of pollen grains to ovules is about eight to one. In 

 flowers which are to be pollinated by the wind, a large number 



1 The teacher is referred to Yearbook of the Department of Agriculture for 

 1900 for data on the insect which pollinates the Smyrna fig. 



The staminate flower of the corn. Notice the hang- 

 ing anthers full of pollen. 



