VARIATION 



29 



In experiments on lower animals, e.g., the protozoa, the same difficulty 

 is met with as has been encountered in bacteria and yeasts, in that it is 

 manifestly impossible to distinguish between somatic and germinal 

 variations. Moreover, in most of these experiments, as with most of 

 those on higher animals, the necessary conditions for rigid scientific 

 analysis have been lacking. Either the same strain as was subjected to 

 artificial conditions was not grown for comparison under natural condi- 

 tions or else the conditions themselves were not sufficiently well con- 



FIG. 12. Leaf and cluster of fruit of Red Cherry tomato of the second generation 

 (right) ; same of the sixth generation (left) of continuous treatment with excessive amount of 

 dried blood. (Photo by T. H. White.} 



trolled to permit of certain analysis. It is interesting to note that the 

 pomace fly, Drosophila ampelophila, which has produced more mutations 

 so far as we know than any other organism, was subjected to the effects 

 of ether on a grand scale and under controlled conditions by Morgan, 

 but that not a single mutation was observed to result from this treat- 

 ment. However, mutations have subsequently appeared again and 

 again in cultures of " wild " flies not only of this species but also of other 

 species of Drosophila. Thus it appears that germinal variations fre- 

 quently occur independently of external stimuli. It also seems that a 

 tendency" to produce mutations may be inherited* 



