THE OUTLOOK FOR PLANT BREEDING. 93 



arguments, however, were directed toward discovering the mechan- 

 ism by which such variations could be preserved and built into 

 different species. To him, the cumulative action of selection 

 formed such a mechanism. Such action, however, was supposed 

 to require centuries and even longer periods of time to result in any 

 marked changes. 



The world drifted along with little change of understanding on 

 this subject until the appearance of DeVries' Mutation Theory in 

 1900, which opened a new epoch in the study of evolution. DeVries, 

 while believing in the importance of natural selection, claimed that 

 the change in species did not take place by slow accumulation, but 

 by sudden leaps or mutations, such as illustrated by the case of the 

 sweet pea cited above. He asserted that plants at certain periods 

 show a tendency to produce marked variations strikingly different 

 from the mother type and that if these mutations were of such a 

 nature that they better fitted the plant to fight the battle of existence, 

 they would be preserved by natural selection and a new species 

 would have been immediately and suddenly formed. 



The belief of Darwin and his followers, that very long periods of 

 time were required to produce marked changes, practically precluded 

 the possibility of subjecting evolution to experimental study and 

 demonstration. DeVries, however, established the experimental 

 method of studying evolution and marshaled a great array of ex- 

 perimental evidence to substantiate his theories. He found the 

 evening primrose {(Enothera Lamarckiana) to produce a number of 

 markedly different variations and these he studied carefully by 

 cultural methods. He found Lamarckiana to break up into a 

 number of different types, each of which, if isolated, would repro- 

 duce its characters practically true to seed. As a result of his 

 extended experiments, he concluded that evolution and the forma- 

 tion of new types or species take place normally and commonly 

 by the production of mutations or marked variations. 



The bearing of DeVries' claims on the methods or art of plant 

 breeding would, if true, cause a profound change. Selection may 

 be said to form the backbone of the breeder's art. Long before 

 Darwin's time the importance of selecting seed from the best in- 

 dividuals came to be recognized. Largely as a result of Darwin's 

 theory of the cumulative action of selection, the modern method of 



