Heredity in Population and in Pure Lines. 11 



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a statistical foundation which can not be easily set aside. Johann- 

 sen has not disproved the idea that selection shifts the mean. 

 It is evident that he could not have done this had his methods 

 been correct. The onus of the argument is with those who hold 

 the idea valid. 



Johannsen's results seem to pave the way for a partial 

 solution of the long vexing problem of the value of continued 

 selection as against the view that changes arise in a saltatory 

 manner. The application of the biotypic hypothesis leaves 

 little ground for dispute between the two schools. Selection 

 must be considered as a purely subjective process and its result 

 is merely the isolation of a form or type, differentiated to a great- 

 er or less degree. If germinal variations are not present in the 

 organism, then selection avails nothing. Johannsen has shown 

 that fortuitous geiminal variations of very small magnitude 

 may exist. Such variations are so small that they would easily 

 escape notice without a critical analysis. They are neither neces- 

 sarily meristic nor morphological in character. It is evident that 

 variations of this nature, mean weight of seed, etc., have been 

 confused heretofore with mere fluctuating variations. The 

 value of selection from a "population" may be considered as a 

 purification of the race and not a shifting of the type. Johann- 

 sen applied the term "biotypes" to the vaiious pure lines that 

 breed true and which are sensibly different from one another. 

 The term is a good one but it should be used in a plastic sense, 

 at least until we know more of what constitutes a "biotype." 



Inasmuch as we find biotypes in cultivated varieties, their 

 origin must be comparatively recent. If, as seems likely, their 

 presence affords the basis for improvement in selection, then it 

 is probable that they are arising more or less constantly. In 

 course of time it may be shown that their appearance is depend- 

 ent upon definitely controlled cultural conditions. But we 

 must assume that they also arise in a truly fortuitous manner. 

 From these considerations it appears that continued selection along 

 some definite line may bring about certain results. But this 

 would only happen if the variations were taking place along the 

 line of selection. An analysis of the material comprising the 

 variety and a study of some of the pure lines for one or two sea- 



