MORE ABOUT POLLINATION 



301 



flowers are sessile. In addition to dandelion and daisy, 



the asters, the jgoldenrods, sunflowers, wild lettuce, thistle, 



burdock, and many other common weeds belong to the 



Composita. Though all Com- 



positcB have their flowers in heads, 



not all plants with heads are 



CompositcB. White and red clover 



have their flowers in heads, and 



they belong to the pea family 



(Leguminosm) . The buttonbush 



and the sycamore also bear their 



flowers in heads. 



b. Determinate Inflorescences. 

 — Of this type the cyme is the 

 only one of importance. (See 

 Figure 12 j.) It is illustrated by 

 the geranium and by the syringa. 

 In a cyme the terminal or central flower blossoms first, and 

 after that only buds already formed open out into flowers. 



Fig. 122. — An umbel of milk- 

 weed. Note that the pedicels 

 all start from the same place. 

 Note the whorl of bracts at 

 the top of the peduncle. 



64. More about Pollination. — Pollen escapes from the 

 anthers which produce it. After its escape any one of a 

 number of things may happen to it. It may be blown by 

 the wind, it may be carried away by an insect, it may 

 fall to the ground and perish. It may reach a stigma or 

 it may not. Most of it does not. 



A . The Waste of Pollen. — For nearly all of the pollen 

 which is produced there is no such thing as pollination; 

 not one grain out of a hundred reaches a stigma. This 

 "waste " of pollen is much greater in wind-pollinated plants 

 than it is in insect-pollinated ones. The chance that a 



