92 HOW ARE ANIMALS AND PLANTS DEPENDENT? 



stxgmct 

 anther 



How does pollination take place in a daisy ' 



Cross-pollination of clover. In a clover head, which is a closely 



massed cluster of little flowers, cross-pollination is usually effected 

 s by bumblebees which work 



rapidly from one flower to 

 another in the same group, 

 inserting their tongues deep 

 into the flower cups. 



Cross-pollination of a 

 composite head. The 

 daisy, aster, and sunflower 

 are examples of a com- 

 posite head. The flower 

 cluster has an outer circle 

 of green parts which look 

 like sepals, but in reality 

 are a circle of leaflike 

 parts. Taken together 



these form an involucre (in'v6-lu-ker). Inside the involucre is 



a whorl of brightly colored, irregular flowers called the ray flowers. 



They appear to act, in some instances at least, as an attraction to 



insects by showing a . , ^ 



definite color (see the 



common yellow A THlll \Y\Y P 



daisy). The flowers 



occupying the center 



of the cluster are the 



disk flowers. Pollen 



is carried easily from 



one flower to another 



even by an insect 



which crawls. 

 Devices to secure 



cross-pollination. 



There are many other 



examples of adapta- 

 tions to secure cross- 



,,. . , The length of the filaments and height of the stigma may make 



pollination by means the self -pollination of loose-strife impossible. Why ? 



