INTRODUCTORY 267 



organs which you have been studying are also the result 

 of long evolution ; in fact, everything which exists to-day 

 has evolved from what existed in the past. It may occur 

 to you to wonder, since flowers and the nutritive organs 

 evolved together, why there is such general similarity 

 among leaves, for example, and such general dissimilarity 

 among flowers. The answer is that, to do their work 

 successfully, leaves need to have one general kind of 

 structure, while, as to flowers, many different kinds of 

 structure have proved to be successful. 



That method of reproduction with which flowers are 

 concerned is, as you know, the sex method. Almost all 

 of the lower plants (ferns, mosses, mushrooms, etc.) , though 

 they do not produce seeds, do possess this sex method of 

 reproduction. They possess structures whose appearance 

 and behavior is like the appearance and behavior of certain 

 parts of the flowers. To study them gives a clear idea of 

 the way in which the flower probably has evolved, for 

 some of these lower plants which exist to-day are much 

 like the remote ancestors of the flowering plants. To 

 study them throws much light upon the evolution of the 

 seed habit, for the seed habit has evolved from the simpler 

 reproductive habits of plants which did not produce seeds. 



The making of seeds is an elaborate process. In this 

 chapter we can tell you how the various parts of the flower 

 are concerned in that process, but the real meaning of the 

 process you will understand only after you have read the 

 chapters about plants which do not produce seeds. 



D. Flowers as Sex Organs. You have been told that 

 the flower is not a sex organ (page 58). But you have 

 also been told that it is concerned with sex reproduction; 



