THE INSECTS: HEXAPODA 



91 



Relations between Insects and Flowers. In order to make 

 seed, the flowering plants require to have the pollen furnished 

 by the stamens (Fig. 52, 1) carried to the pistil (Fig. 52, 2) of 

 the same kind of plant. The pollen is necessary to the ferti- 

 lization of the ovule (Fig. 52,3), which afterwards grows into 

 the seed. Continuous pollination of a plant by pollen which 

 it furnishes from its own stamens has been found to be detri- 

 mental to the vigor of the 

 seeds. We find in nature 

 many devices to insure 

 fertilization by pollen 

 from another plant of the 

 same kind, that is, by 

 cross-pollination. 



Waite, Year-book, United States Depart- 

 ment of Agriculture, 1898) 



1, stamen; 2, pistil; 3, ovule 



Some plants have the 

 stamens and pistils so 

 placed in the flower that 

 no pollen can fall from 

 one to the other; some 

 ripen their stamens and 



pistils at different times. FIG. 52. Diagram of Pear Flower. (After 

 Many have the stamens 

 and pistils on separate 

 plants, and a great num- 

 ber, though the stamens and pistils are close together, are 

 wholly or partially sterile to their own pollen, and " set " their 

 seeds only if the pistils receive pollen from the stamens of 

 another plant of the same species. This is the case with many 

 of the fruit trees. 



The wind carries pollen for some plants which have their 

 stamens and pistils more or less exposed, but a great number 

 of plants, especially those with the most beautiful flowers, 

 depend on insects to bring about pollination. So far has 

 this dependence gone that, in many cases, plants have become 



