14 PLANT-BREEDING 



some beautifully twisted specimens. I succeeded in procur- 

 ing such a specimen in this species by cultivating a race of it 

 during some few years, selecting the specimens which 

 showed a marked tendency toward variation in the arrange- 

 ment of their leaves. The twisting appeared at once, but 

 the race has not been continued. 



All these, and many other, experiments have been con- 

 ducted under conditions which allowed of a close scientific 

 study. They confirm the common experience of the horti- 

 cultural breeder in stating the suddenness of the changes 

 and the immediate production of distinct races. They 

 show us the way in which analogous changes may have 

 occurred in nature, and make it probable that sudden changes 

 are, at least, an important factor in the evolution of the 

 vegetable kingdom. 



With agricultural crops my experiments have been too 

 rare to give a definite result. The German breeders assumed, 

 as a rule, that they produced their races at will and by a 

 process of slow variability and repeated selection. It is 

 mainly upon this conviction that Darwin has based his con- 

 ception of an analogous slow improvement of species in 

 nature. This German method, however, has been sub- 

 mitted to a severe criticism by Dr. Nilsson, the director of 

 the Swedish agricultural experiment station at Svalof. 

 His pedigree-cultures have shown that the idea of a slow 

 accumulation of characters by repeated selection is due to 

 incorrect observations and to the use of untrustworthy 

 methods. According to his experiments, changes occur in 

 agricultural plants as suddenly as in horticultural species; 

 there is no essential difference between them in this respect. 

 By these discoveries the main support of the theory of slow 

 and gradual evolution is broken down, and the analogy 

 between artificial and natural production of species comes 

 to plead wholly for the theory of mutation. These new 



