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. LHither 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. 
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