THE AMERICAN BOTANIST 97 



a single plant to the acre." He also says "it is evident that 

 tlie resisting ai)ility increases from year to year, from gener- 

 aLit)n to generation, even in a pure, pedigreed strain which 

 came originally from a single non-resisting seed." 



In this operation of producting fully resisting plants 

 from non-resisting stock there is no trace of selection. There 

 were no deaths of weaker plants and survival of more resis- 

 tant ones. It is a plain case of resisting power increasing 

 from generation to generation, and the thing to be considered 

 is the source of that increase. The experiment just described 

 is not affected in the least by the fact that Bolley carried on 

 another experiment at the same time at another place on an- 

 other plant. Neither would it be affected if he had carried 

 on a thousand other experiments at a thousand other places. 

 Nor would it be affected by any accident which happened to 

 any one of such other experiments. 



Flax is a self-fertilized plant not known to cross poWx- 

 nate when left to itself. When the experimentor gets resis- 

 tant plants from non-resistant stock, the pedigree of the re- 

 sistant plants is that set forth in the experiment stated. Noth- 

 ing in the way of improvement by selection would appear if 

 lie sowed a whole field with seeds instead of planting one seed, 

 and part of the resulting plants should die. The death of 

 one plant docs not add anything to the resisting power of a 

 sister plant on the other side of the lot, and increased resisting 

 power is the thing which was obtained. 



There is a sharp distinction between the experiments re- 

 ferred to by Dr. Gaines and those carried out by Prof. Bolley. 

 When a pure line is raised year after year under uniform dis- 

 ease infection, selection is powerless to bring about any im- 

 ])rovement in disease resistance. When a pure line is rai.sed 

 year after year under gradually increasing infection, improved 



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