228 Heredity and Eugenics 



forces with selective accumulation, provided the impact of 

 the external forces is not made too intense. In other words, 

 variations properly combined lead to more definite results in 

 the modification of pattern than the more vigorous methods 

 which are productive of permanent changes in color. It is 

 therefore necessary to distinguish between the modifications 

 of color and modifications of color pattern, because pat- 

 tern may well be present as an attribute without revealing 

 itself, and it only reveals itself when something in the 

 organism results in the deposition of color in the proper 

 location. 



In the experimental modification of organisms, the pat- 

 tern has been one of the characters least influenced. In 

 DeVries' experiments with plants the pattern was modified 

 relatively little, if at all, the principal changes in Oenothera 

 being in leaf proportion, leaf arrangement, color, and 

 similar characters, which are properties of the whole and 

 which are known to vary with more or less readiness in all 

 organisms. In the same way the experiments which have 

 been carried out on insects by Dorfmeister, Weismann, 

 Fischer, Edwards, Standfuss, and many others, show modi- 

 fications in the color and little or no modification in the 

 pattern. In some specimens the pattern is obscured by the 

 spreading of the color from the original area into contiguous 

 portions, but the fundamental pattern itself is not altered, 

 as shown by the fact that in most of these experiments in 

 the next generation the progeny revert to the pattern of 

 the normal parental stock. 



In MacDougal's experiments with plants, and in Gager's 

 also, the pattern appears to be only slightly modified, if at 

 all, and in all of the plants used by them the pattern was 

 relatively simple, both petals and leaves being self-colored. 



