The Origin of Species 311 



limits of species are often very difficult to decide, 

 and no two students of any large genus of plants 

 agree exactly as to the number of species within 

 the genus. How these species have originated is 

 a vexed question which for the last generation has 

 aroused an amount of speculation, and even acri- 

 monious controversy, that would seem to show that 

 men of science are not much behind the theologians 

 in their defense of the true faith against the at- 

 tacks of heretics. 



THEORIES OF EVOLUTION 



The idea of evolution is a very ancient one, but 

 until the iQth century evolutionary theories were 

 too vague to attract any general attention. Dar- 

 win's great service to science is not that he first 

 enunciated the principles of evolution, but that by 

 rigorous experiment and observation he made the 

 fundamentals of evolution so clear that henceforth 

 they could not be ignored. Especially did he make 

 evident the enormous importance of natural selec- 

 tion in the evolution of new forms of life, and the 

 origin of species. As Darwin's studies included 

 plants as well as animals, and covered an extensive 

 range of topics connected with some of the most 

 important botanical problems, the debt of the bot- 

 anist to Darwin is a very great one. The botanical 

 student will remember, however, that during the 

 ten years preceding the appearance of Darwin's 



