104 VARIATION IN LEPTINOTARSA. 



In the section on variation I have shown that these two specie?, decemline- 

 ata and multitarniata, are the parents of many extreme variates (mutants). 

 In a species which is wide-ranging and highly variable, both individually and 

 as to place, which is highly susceptible to environmental change and shows 

 strong place variation, is there any relation of this phenomenon to the pro- 

 duction of sports or mutants? and, if so, what? As far as my evidence goes, 

 it is certain that in the second generation of 1903, at Guadalupe, the per 

 cent of the form melanothorax was 2.4, or more than ten times the normal 

 under average conditions at that place. Now, this was not accidental, for 

 in the same year and in a corresponding generation the per cent was 3.1 

 at Puebla, which is more than thirty times the normal proportion of this 

 variation at that place. The condition in the environment produced a wide 

 place variation at the time and a larger percentage than normal of extreme 

 variations ; whereas in succeeding generations the place variation was oblit- 

 erated and the normal per cent of melanothorax appeared. These observa- 

 tions would point to the conclusion that the change in the population for a 

 given generation due to place variation gave opportunity in the deviation of 

 the entire population from the normal, for a larger percentage to appear as 

 extreme variations. From observations in nature it is difficult to tie results 

 to special causes, to be sure that what we see happen is the result of this or 

 that cause. Likewise in this case it looks as though there were an important 

 and fundamental relation between this place variation and the production of 

 numerous sports or extreme variations in multitceniata. In 1904 I observed 

 that at Tierra Blanca the unusual condition of excessive precipitation pro- 

 duced angiistovittata from imdccimlineata in abnormal proportion, and the 

 same has been found in deccrnlincata. De Vries found that in some years his 

 Oenothera lamarckiana mutants were more abundant than in others. Is it 

 not possible that had he investigated he would have found here also this same 

 relation ? If this relation between place variation and the abundant produc- 

 tion of extreme variations in plastic species be generally true, and it certainly 

 is for this genus of beetles, are we not a step nearer to understanding better 

 the nature of mutants and the manner in which they are produced? Is it not 

 possible also that here too we have a clue as to how we shall proceed in order 

 to produce experimentally these variations? 



Place variation must, I believe, be regarded as a phenomenon of impor- 

 tance, not only in its possibilities for producing false appearances, but also 

 because of the relation which it seems to bear to the appearance of extreme 

 variations or mutants. Whether or not it is of any moment in evolution by 

 slowchangeswe are not yet in a position to determine, but our evidence would 

 seem to indicate that it is not, as its flucuations are about equal on either side 

 of the average. Long-continued observation of this phenomenon would be 

 highly important, as it would perhaps go a long way towards settling some 

 disputed points regarding the method of evolution in animals. 



