FLOWERS AND THEIR USES 



273 



no nectar, or practically none. The insects that visit such 

 flowers eat the pollen instead of nectar ; and the flowers 

 produce so large an amount of pollen 

 that, although a good deal is eaten by 

 an insect visitor, enough clings to its 

 body so that it is sure to carry some 

 pollen to the next flower that it visits. 

 This method of providing food for in- 

 sects is by no means economical of 

 pollen ; but it is probably less extrava- 

 gant, after all, than wind-pollination. 



283. Insects that Lay their Eggs in 

 Flowers : the Yucca Moth. — In some 

 cases, an insect visits a flower, not to 

 obtain food for itself, but to lay its eggs 

 in a place where its young, when the 

 eggs hatch, may find 

 food, or shelter, or 

 both. The Yuccas, liv- 

 ing in the southern United States and 

 Mexico, are members of the lily family, 

 with sword-like leaves and a tall stalk that 

 bears many white flowers (Fig. 160). The 

 flowers of various species of Yucca open 

 at twilight and are visited by a certain 

 night-flying moth. The female moth 

 alights first on an anther. There she 

 scrapes up a mass of the sticky pollen 

 grains and rolls them into a ball. After 

 the pollen is gathered, the ball is tightly 

 held by a special long, fiexible organ. 

 Then the moth vi.sits a pistil (usually of 

 another flower) , and by means of a sharp- 

 pointed organ she pierces the ovary wall and deposits her 

 eggs in the ovary among the ovules. Finally she visits the 



Fig. 160. — Yucca glo- 

 riosa. After Kemer. 



Fig. 161.— The 

 Yucca moth gather- 

 ing pollen from an 

 anther. After Riley. 



