278 FLOWERS 



than nutritive organs are. This is true for plants without 

 flowers as well as for plants with them. 



The differences between kinds of flowers are differences 

 between their sepals, petals, stamens, and carpels. These 

 organs vary in number, in shape, in color, in size, in rela- 

 tive position, and in various other ways. 



A . The Evolution of Flower Forms. — We are far from 

 understanding all the laws of evolution, but we do under- 

 stand a good deal about the evolution of flowers. We can 

 see clearly that certain kinds have evolved from certain 

 other kinds, that the more complex forms have all come 

 from simpler forms, and that all forms which are success- 

 ful appear to have certain pecuUar advantages of their own. 



It is no simple matter to determine the true relation- 

 ships of plants even by means of their flowers. To tell 

 which plants are related to which is a great puzzle upon 

 which botanists are still at work. They are trying to find 

 out the true genealogy or " family tree " of plants. In 

 this work the flowers have been of great aid, and the 

 real kinships of flowering plants are better understood 

 than the kinships of groups which do not bear flowers. 

 Yet it has taken many years of work by many men to' 

 determine even the general relationships of flowering plants 

 to each other. 



Linnaeus, a Swedish botanist, was one of the first great 

 classifiers of flowering plants. He recognized the flowers 

 as the best basis for classification, but he had no means of 

 knowing which flowers were derived from which. So he 

 divided them into two great groups on the basis of the 

 number of stamens. He put in one great group all those 

 plants whose flowers have ten stamens or more; he put 



