442 PROCEEDINGS OF THE ACADEMY OF [June, 



parts of two great physiographic provinces, the Piedmont Plateau 

 and the Coastal Plain. These correspond, as Stone has clearly 

 shown in the work already cited, respectively to the Transition and 

 Upper Austral biotic zones of Merriam. The dividing line between 

 two is accordingly the "fall-line" which marks the line along which 

 the hard rocks of the Piedmont Plateau meet the soft and incoherent 

 deposits of the Coastal Plain. 



Without a more detailed knowledge than we actually possess of 

 the life history and of the developmental and growth requirements 

 of Orthoptera, it is impossible at present to give a full causal explana- 

 tion of the observed differences between the Orthopteran faunas of 

 the Piedmont Plateau and Coastal Plain. Merriam regards tem- 

 perature as the controlling factor, and he is probably right if by 

 temperature he means the temperature of the medium in which the 

 organism undergoes its development and growth, and this in a given 

 locality might be very different in one kind of medium from what it 

 is in a different kind, a difference which would not be shown by a 

 record of the atmospheric temperature alone. Some of the Coastal 

 Plain grasshoppers, which in this region are entirely absent from the 

 Piedmont Plateau, exist in much higher latitudes, as in Massachu- 

 setts or Ontario, where the sum of the positive atmospheric tem- 

 peratures for the season of growth and reproduction is much less 

 than in our local Piedmont, l^ut they doubtless exist there under 

 conditions in which they receive a greater amount of heat at the 

 critical time than they would under entirely different conditions in 

 a region which, like our Piedmont, is warmer so far as general atmos- 

 pheric temperatures are concerned. 



Although temperature is probably the fundamental distributional 

 factor, there are good reasons for questioning if it is the only factor. 

 The environment of any organism or group of organisms is a complex 

 of factors, each of which may act directly on the organism and influence 

 its activities. Shelford, for example, has shown that in the case of 

 certain species of tiger-beetles^ the distribution depends upon the 

 simultaneous presence of a number of conditions, all of which must 

 be fulfilled if the species is to maintain itself. 



In our region the great contrast between the biotas of the Piedmont 

 and Coastal Plain provinces is at least empirically — and doubtless 

 in some way causally — -correlated with well-marked differences in 

 the prevailing types of soil. In the Piedmont the soils are residual, 



« Shelford, V. E., Physiological Animal Geography, Jour, of Morph., Vol. 22, 

 1911, pp. 551-618. 



