22 



THE VARIATION AND CORRELATIONS OF 



5. GEOGRAPHIC VARIATIONS. 



Environmental influences are usually classed as "edaphic" and "cli- 

 matic." Edaphic factors are, properly speaking, soil factors, but the 

 term may be used in a more general sense to include all environmental 

 influences which are local in character. We were concerned with these 

 in the preceding section. Climatic factors, except in mountainous 

 regions, differ but slightly in not distantly separated localities. Geo- 

 graphic variation is usually, although not necessarily, a function of 

 these climatic factors, past and present, of the environment. 



TABLE 11. Average lengths of ovipositor, tegmina, and wings, and the relative 

 abundance of the wing dimorphs at various localities. 



From table 11 it seems that there is no relation between latitude and 

 the length of the ovipositor. We have just seen that there is, appar- 

 ently, a close relation between the length of the ovipositor and the 

 edaphic environment. We might expect that, given the same sort of 

 soil, the ovipositor would be longer in the north than in the south. 

 Such does not seem to be the case. From observation, the conditions 

 at Perkins Cove, Maine, seem to be similar to those at the base of the 

 spit at Cold Spring Harbor, New York, except for the differences in 

 climate. The length of the ovipositor is also practically the same. 

 Unfortunately, these are the only two localities which I can compare 

 from personal observation. They are both beach populations. If we 

 compare the Amherst, Massachusetts, collection (from "fine soil mixed 

 with clay") with the Gotha, Florida, collection ("stony waste land"), 

 we find that the ovipositor of the northern lot is shorter than that of 

 the southern one, but the difference is only a trifle more than that 

 between the two extreme collections from Cold Spring Harbor, and 

 may be accounted for by soil differences. In other words, it seems that 



