296 PRODUCTION OF RACES AND SPECIES IN LEPTINOTARSA. 



own experiments I have used for three years past salt solutions as well as 

 electric stimuli, with the same results as are described in this paper for tem- 

 perature and moisture, and in all their action is simply as a stimulus, and 

 nothing more. The same is also probably true in MacDougal's plants. In 

 plants we shall undoubtedly find that the influence of salt solutions is far 

 greater than in animals, owing to the intimate relations of plants to the soil. 



MacDougal admits that he has not been able to analyze the manner in 

 which this result is brought about in the germ plasm, and it seems to me a 

 waste of time and energy to speculate upon this point until we have some 

 direct investigation of this problem. 



Of considerable importance is the strong evidence which points to the gen- 

 eral conclusion that these permanent variations arise during the growth 

 periods of the germ cells, and do not appear to arise before or after this 

 period. Just what this signifies is at present difficult to determine, further 

 experiments and cytological studies being necessary before we shall be able 

 to arrive at a more complete understanding of it. 



