(4) 



diverse strains, called "pure lines", "clones", or "bio- 

 types", differing from each other, but each one constant 

 and invariable in its c\"n hereditary constitution. This 

 last idea, that every individual of any given clone is 

 precisely the sane in its genetic make-up as any otVier 

 individual of the same clone, is the basic idea of the pure 

 line concept. As a corollary, it follov/s that all the vari- 

 ations four-d within .a single clone are piirely somatic and 

 not heritable. In this case, it is evident, ^.-election 

 working witliin a clone could have no effect. The testing 

 of this hypothesis, then, is of the greatest importance for 

 any general consideration of t'ne mechanism of evolution. 



This problem has already attracted the attention of 

 numerous investigators. 3ome have com.pletely comfirred the 

 conclusions of Johannsen. Tiie more important of these papers 

 have already been cited. But t?iere are others who have 

 maintained that hereditary variations do occur within clones, 

 and that selection withi.n a clone may have an effect. 



Pearson (1910), subjecting the data of the earlier 

 pure line workers to a more accurate statistical analysis, 

 found evidence indicating that such inheritance might exist. 

 otout (1915), stocking U915), Middleton (1915), and Jennings 

 (1916) have all succeeded in isolating, by selection, heredi- 

 tarily diverse strains within single clones. The present 

 paper adds another similar case to this list. 



Problems. Accepting, as we must, the fact that 

 th.ere do exist, within a single species, diverse strains or 

 races, there are two main problems which claim our attention. 



