INTERRELATIONS OF PLANTS AND ANIMALS 43 



pillars eat some of the devel- 

 oping seeds and later bore 

 out of the seed pod and 

 escape to the ground, leav- 

 ing the plant to develop 

 the remaining seeds without 

 further molestation. 



The fig insect {Blastophaga 

 grossorum) is another mem- 

 ber of the insect tribe that 

 is of considerable economic 

 importance. It is only in The pronuba polli- 

 recent years that the fruit "f^^^ *^^ p^*^ 



^ of the yucca. 



growers of California have 

 T, , . , . discovered that the fertilization of the female 



Pod of yucca showing 



where the young pro- flowcrs is brought about by a gallfly which 



nubas escaped. bores into the young fruit. By importing 



the gallflies it has been possible to grow figs where for many 

 years it was believed that the climate prevented figs from 

 ripening. 



Other Flower Visitors. — Other insects besides those already 

 mentioned are pollen carriers for flowers. Among the most use- 

 ful are moths and butterflies. Projecting from each side of the 

 head of a butterfly is a fluffy structure, the palp. This collects 

 and carries a large amount 

 of pollen, which is deposited 

 upon the stigmas of other 

 flowers when the butterfly 

 pushes its head down into 

 the flower tube after nectar. 

 The scales and hairs on the 

 wings, legs, and body also 

 carry pollen. 



Flies and some other in- 

 sects are agents in cross- 



pollination. Humming birds ^ ^^^^^,,^ bird about to cross-pollinate 



are also active agents in a lily. 



