NILSSON'S DISCOVERY 37 



into German by Dr. Hesse for the use of the general public. 

 It is largely devoted to the description of the superior qual- 

 ities of his varieties, and the historical evidence concerning 

 their origin is only incidentally given. From his statements, 

 we may gather that at first he assumed his mother plants 

 to be sports, but afterwards took them to be simply old con- 

 stituents of the ordinary cultivated varieties. He observed 

 these to be mixtures, consisting of more and of less abun- 

 dantly yielding types, and on this observation founded the 

 method which he followed during the latter part of his life. 

 He satisfied himself that even within these mixtures the 

 constituents were uniform and constant races, and there- 

 fore it was only natural that after isolation they would re- 

 main so. Shirreff seems not to have had any idea of the 

 possibility of the existence of another form of variability 

 as a starting point for further improvement. Considering 

 the great importance which has been conceded in Germany 

 to this possibility, even during the latter part of Shirreff's 

 life, it is not without interest to lay some stress on this fact. 

 The more so, since he had in mind the desirability of other 

 ways to reach the same purpose more surely and more 

 quickly. He turned himself to hybridizations and made 

 some valuable experiments on the crossing of cereals, and 

 from his statements it seems quite evident that he did so 

 only in the firm conviction of having exhausted the possibili- 

 ties offered him by variability alone. 



Le Couteur and Patrick Shirreff seem to be the only 

 breeders of cereals who have worked on the principle of one 

 single initial selection and of subsequent rapid multiplica- 

 tion without renewal of the choice and without isolating the 

 best individuals during the following generations. On this 

 point they are to be considered the precursors of the method 

 which has of late been discovered anew, at Svalof. But 

 they had only a very limited appreciation of the importance 



