48 



BIOLOGY AND HUMAN LIFE 



tain nectar. Some of these insects also use pollen as food. The 

 bees, for example, feed quantities of pollen to the young in their 

 hives. In getting pollen or nectar the insect rubs off pollen 

 on various parts of its body. Later, when it visits another 

 flower of the same kind, the pollen is rubbed off against the 

 stigma (see Fig. 23). 



39. Adaptations in flowers. Wherever we see a living thing 

 we cannot help being impressed by the ''fitness" of its parts 

 and of its activities. The organs and functions are beautifully 



related to one another as 

 members of the organism, 

 and they are beautifully re- 

 lated to the surroundings, 

 making life possible. Thus 

 in the flowers we may see 

 the wonderfully delicate 

 structures bearing pollen 

 and ovules. Many flowers 

 close toward sunset and 

 open again at dawn, expos- 

 ing the anthers and stigmas 

 to insects by day but pro- 

 tecting them at night. The 

 various colors in the corolla, 

 the odors, the nectar, all very evidently attract insect visitors. 

 The curious shapes match almost perfectly the sizes and shapes 

 of particular insects. The stigma is rough, or hairy, or sticky, 

 just right for catching pollen, and bears the fluid in which the 

 pollen sprouts out the pollen tube. Inside the style there is a hol- 

 low passage or a spongy structure through which the pollen tube 

 readily works its way. The pollen tube's irritability guides it 

 toward the ovule. In the ovule is the micropyle, through which 

 the pollen tube finds its way to the embryo sac. And we could 

 go on multiplying illustrations of the remarkable adaptation 

 of part to part and of all to the conditions surrounding the plant. 

 Of course the same may be said of the many details that make 



Fig. 21. Stigma of a grass 



In wind-pollenated plants the stigmas usu- 

 ally expose a large surface to the wind. A 

 study of conditions on farms that produce 

 corn, wheat, oats, and other grains shows that 

 these plants, as well as many others, depend 

 entirely upon the wind for their pollenation. 

 Indeed, it is sometimes necessary to take 

 special precautions to prevent the wind from 

 bringing to a group of plants an undesirable 

 kind of pollen from a remote field 



