DEVELOPMENT OF PLANTS 477 



rence in many genera of perennial underground stems, which 

 make them to a degree independent of climate conditions and the 

 depredations of grazing animals. A great many are avoided 

 because of their protective armor of prickles, bitter, acrid juices 

 or oils and resins. Especially to be noted is the seed-like fruit 

 with its numerous devices for distribution. All these features, 

 among others, explain their extensive distribution in open coun- 

 tries. Without doubt the greatest advantage appears in the 

 structure of the flower and the inflorescence. The highest type of 

 a flower, as in the case of a machine, is the one that is most effi- 

 cient. The flower is not so elaborate as the orchid or as those of 

 some other groups, but it is superior because it accomplishes its 

 work with greater certainty and more economically. Note the 

 significance of these facts — the ovary of the orchid consists of 

 three carpels which may produce thousands of seeds, whereas 

 the simple ovary of one of the Compositae contains but a single 

 seed. Reduction has been made in every part without loss of 

 conspicuousness and variations have also appeared that practi- 

 cally eliminate the uncertainties of crossing and autogamy, and 

 consequently the formation and distribution of the seed is en- 

 sured. In a word every evolutionary tendency that you have 

 noticed in the development of the flower finds its expression in 

 this group of plants. 



