THE EVOLUTION OF PLANT REPRODUCTION 



71 



of the daisy or dandelion, where each flower — in the popular 

 sense — is in reality made up of thousands of tiny strap-shaped or 

 tubular flowers which form the ray and the disc of the flower- 

 head (fig. 44). Composite flowers form those spectacular blooms 

 of the plant kingdom — the chrysanthemums and dahlias. 



Outside of the corolla, many flowers produce another whorl 

 of leaf-like green structures — the sepals. Sepals are collectively 

 known as the calyx, whose chief function is to protect the flower 



DfSC FLOWER RAY FLOWER 



Fig. 44. — Composite flowers are grouped in heads, often as in the sunflower 

 diff'erentiated into ray flowers and disc flowers. 



when in oud and to support the corolla. But in many cases the 

 sepals have assumed the function of attraction, and then resemble 

 petals. Among the anemones, clematis and cowslip, for example, 

 the flowers lack petals and colored sepals take their place. In the 

 common four o'clock, likewise, there are no petals, the fused 

 calyx being colored to attract insects. 



In other cases, additional structures are pressed into service 

 by the flower for the function ordinarily assumed by the corolla. 

 Bougainvillea has small inconspicuous flowers, but they are 



