THE EVOLUTION OF PLANT REPRODUCTION 



69 



flower parts serve to attract the animals for this purpose, acting 

 as colorful and conspicuous signboards to arrest the attention of 

 the animals. Frequently these attracting structures of the flower 

 are so large and prominent that they seem the most important 

 part, obscuring the stamens and pistils which are the real 

 reproductive organs. Thus the flower has come to serve a dual 

 purpose; in addition to the primary function of producing pollen 

 and ovules, in stamens and pistils, it has as its duty also the at- 

 traction of animals who unwittingly carry pollen from one flower 



PETAL 



STAMEN 



Fig. 41 . — ^A complete flower consists of petals, forming a whorl known as 

 the corolla; sepals, forming another whorl known as the calyx; stamens; and 

 pistils. 



to another (fig. 41). If flowers do not depend upon animals for 

 pollination, they lack these brightly colored parts; but no flower 

 can lack the stamens and pistils if it is to serve the purpose for 

 which flowers have evolved — reproduction. 



Flowers have developed a variety of devices for the attraction 

 of pollinating agents; chief of these are the petals. Petals origi- 

 nally were leaves which through evolutionary history have lost 

 their chlorophyll and in most instances have become white or 

 colored. The whorl of petals which encircles the central pistil 

 and stamens is known in its entirety as the corolla. In the most 



