FLOWERS 



43 



Pod of yucca pierced by 

 the Pronuba. 



gathers pollen from an anther, flies away with this load to an- 

 other flower, there deposits an egg in the ovary of the pistil, and 

 then rubs its load of pollen over the stigma of the flower. The 

 young hatch out and feed on the young seeds 

 which have been fertilized by the pollen placed 

 on the stigma by the mother. They eat some 

 of the developing seeds and then bore out of 

 the seed pod and escape to the ground, leaving 

 the plant to develop the remaining seeds with- 

 out molestation. 



The fig insect (Blastophaga grossorum) is 

 another member of the insect tribe that is of 

 considerable economic importance. It is only 

 in recent years that the fruit growers of Cali- 

 fornia have discovered that the fertilization 

 of the female flowers is brought about by a 

 gall fly which bores into the young fruit.^ 



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 showy corolla to 

 attract insects, often lack this part altogether. In fact we are apt 

 to entirely overlook the flowers which appear in the spring upon 

 our common forest and shade trees. In many trees, as, for ex- 

 ample, the willow, 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 another. Most of our com- 

 mon trees, oak, poplar, maple, and others, are cross-pollinated 

 almost entirely by the wind. 



Among the adaptations that a wind-pollinated flower shows 

 are: (1) The development 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 of the pollen grains never reach their destination and are 



* The teacher is referred to Year Book of the Department of Agriculture for 

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



