NILSSON'S DISCOVERY 31 



English breeders have, as a rule, preferred the more practical 

 line of working, but their results have been isolated, and have 

 not been combined into a definite svstem. German breeders, 

 on the other hand, have followed the theoretical principle 

 of slow amelioration, and have developed this idea into a 

 broad system, which has been applied by several of their most 

 prominent men to the improvement of numerous varieties. 



Darwin, as is generally known, chose the principle of 

 slow and gradual changes as affording the most reliable 

 facts for his discussion of the manner in which species are 

 produced in nature. In doing so, he has brought the Ger- 

 man method to the rank of a scientific principle and secured 

 for it the interest of the students of biology at large, but has 

 almost thrown into obhvion the other side of the question. 



Of late, however, new facts have been discovered, wliich 

 are of a nature to change the whole aspect of this part of 

 the science of evolution. At the Agricultural Experiment 

 Station of Sweden, at Svalof, the German method has been 

 extensively tested, and the result has not been favorable to 

 it. New discoveries have been made which go to prove that 

 the whole principle of gradual changes rests on an insufficient 

 knowledge of the laws of variability of agricultural plants, 

 and may be replaced by more simple and more direct methods 

 as soon as these laws are exactly studied. It is my object to 

 give a survey of the deep significance of these Svalof experi- 

 ments, partly in their practical bearing on agricultural plant 

 breeding, but mainly in their complete compHance with the 

 doctrine of elementary species, and in their appreciation of 

 these as the true material from which selection has to make 

 its choice. I shall endeavor to point out that these new dis- 

 coveries must deprive the principle of gradual ameliorations 

 of its present high rank in agricultural practice, as well as 

 of its significance as a support for the prevailing views con- 

 cerning the origin of species in nature. 



