I20 HEREDITY AND EVOLUTION IN PLANTS 



and yet many, if not most, of the characteristics by which 

 different species are distinguished from each other are of 

 this kind — not, so far as we can see, absolutely essential 

 to the Hfe of the species. Mutation also oiJers a method 

 by which evolutionary changes may take place within a 

 much shorter time-period than was demanded by the 

 natural selection of fluctuations. Incidentally, the muta- 

 tion theory clearly shows that the absence of "connecting 

 Hnks" between species is- not, as was formerly urged, an 

 argument against evolution, but is, on the contrary, just 

 what we might expect to find. 



94. Value of the Mutation Theory. — The elaboration of 

 the mutation theory (together with the rediscovery of 

 Mendel's law, to be discussed in Chapter V) furnished the 

 biological world with a new method of study; it demon- 

 strated that the method of evolution, so far as it concerns 

 the origin of new characters, may be studied by experi- 

 mentation.^ The mutation theory should also be of great 

 service to breeders. It has helped to establish plant and 

 animal breeding on a more scientific basis, has pointed the 

 way to correct methods where men where formerly groping 

 in the dark, and has showed, that results of commercial 

 value do not require a life time, but may be obtained with- 

 in two or three seasons. By the application of modern 

 methods it has been possible, within a few seasons, to 



' Like most great contributions to science, the elaboration of the experi- 

 mental method of approach to the problem of heredity and evolution cannot 

 be attributed solely to any one man. Students of science in any period 

 come into a rich inheritance in the labors of many predecessors. To 

 fully assign the credit for the experimental method in the study of heredity 

 it would be necessary to write the history of investigations extending from 

 Kolreuter (1760) one of the first, if not the first hybridizer, of plants, Knight 

 (1799), through Gaertner (1849), Jordan (i8s3),Naudin (1862), and others 

 to Mendel, de Vries, and those of more recent date, down to our own time. 



