Pollination: or How to Cross Plants 279 



sterile stamens spreading from the base of the cone. 

 These different flowers are borne on different plants in 

 this species of clematis, and the plants are therefore 

 practically dioecious, because the stamens of the pistillate 

 flowers generally bear no pollen. A similar mixed ar- 

 rangement occurs in some strawberries, except that there 

 are no purely staminate flowers. There are purely pistil- 

 late varieties, others, as the Crescent, with a few nearly 

 or quite abortive stamens at the base of the cone of pistils, 

 and others in which the flowers are perfect or hermaph- 

 rodites, that is, containing the two sexes. 



The compositous flowers as the asters, daisies, golden- 

 rods, sunflowers, dahlias, zinnias, chrysanthemums, and 

 their kin need to be considered in still a different 

 category. In these plants, the head, or so-called flower, 

 is an aggregation of several or many small flowers or 

 florets. Each seed in a sunflower head, for example, 

 represents a distinct flower. Sometimes all of these flowers 

 are perfect, contain the two sexes, and sometimes 

 they are pistillate or staminate in different parts of the 

 head; and in some cases the plants are dioecious. In 

 many plants of the composite family, the flowers near the 

 border of the head are unlike those of the center or disk, 

 in having a long ray-like corolla; and these ray-flowers 

 are frequently of different form from the others in the 

 character of the essential organs. Very frequently the 

 ray-flowers are pistillate, whilst the disk flowers are 

 generally hermaphrodite. The anthers in these plants 

 are united in a ring closely about the style and below the 

 stigma. 



The ovary, as we have seen, ripens into the pod, berry, 



