Variation and Heredity 469 



those creatures which survive. Since, moreover, the or- 

 ganisms which survive respond to the influence of the 

 environment, be it much or little, the stamp of environ- 

 ment is ultimately borne by every living thing. This 

 does not imply, however, that the environment stimulates 

 change in the direction of fitness for the particular en- 

 vironment, yet a strictly physico-chemical explanation 

 would perhaps demand this. 



285. Fluctuating variation and the origin of varieties. 

 The artificial selection of fluctuating variations has been 

 the basis of great improvement, or of the maintenance of 

 standards, in many cultivated crops. The sugar content 

 of good varieties of the beet has been increased from be- 

 tween 8 and 10 per cent to from 14 to 18 per cent. Many 

 deny permanence to this type of selection, and much experi- 

 mental work appears to be in progress, designed to throw 

 light upon the question. 



Punnett says : " The small fluctuating variations are not 

 the materials on which selection works. Such fluctuations 

 are often due to conditions of the environment, to nutri- 

 tion, correlation of organs, and the like. There is no in- 

 disputable evidence that they can be worked up and fixed 

 as a specific character." Castle, speaking of the heredity 

 of fluctuations, says, " It is an exceedingly difficult and 

 slow process, and its results of questionable permanency." 



Physiological modifications in corn. Unusually inter- 

 esting experiments in corn variation and breeding have 

 been conducted at the Illinois Experiment Station. In this 

 case variation in chemical content with respect to high 

 protein and low protein, also high oil and low oil, has been 

 made the subject of study, and the results for a ten-year 



