209 



HU iutlnence on the charactei" of the l)iota is not very evident. 

 The fact that some organisms are attracted by the presence of 

 others, only complicates the problem. After casting about for 

 species that appeared to be directly influenced by these condi- 

 tions with the least likelihood of complications of any kind, 1 

 selected the acridiid genus MrldiKiphix. Just why M. Jiuriilns 

 should occur only in the most barren blow-sand situations 

 while M.foiiiir-nilii-iiin seems interdicted by even a suggestion 

 of blow-sand, seems at first sight almost unaccountable. Fac- 

 tors which might possibly have an influence in this case are 

 (1) food supply, (2 I moisture, (3) temperature, (^4) sparseness 

 of vegetation, {b) the mechanical effect of sand, by its drifting, 

 etc., (6l protection. (7) competition, and (S) the effect of sand 

 on the immature stages. 



Considering these factors successively, the matter of food 

 supply might be expected to solve the prol)lem. since McNeill 

 ('91. p. 75, XI. vriirhri) found flariihis constantly associated with 

 the sand-bur {Ccncltriis) which grows on sandy ground; but the 

 sand-bur is locally vastly more wide-spread than finridiis, and 

 in our field-work //r/(vV/».s- was found in blow'outs wdiether sand- 

 burs were present there or not. Morse ('99. p. 315) says that 

 the food (juestion with grasshoppers is a matter of quantity 

 rather than quality, indicating that they have but little pref- 

 erence as to food supply. As to the subject of moisture, 

 there is doubtless at times much difference between sand and 

 ordinary soil in this respect. Capillary action is stronger in 

 ordinary soil, which therefore dries out more deeply, and at 

 the surface more slowly, than sand: but ultimately one is as 

 dry as the other. The factor of atmospheric humidity at close 

 range with the soil may have some influence upon these geoph- 

 ilous species, as its variations over sand and earth would doubt- 

 less l)e expressed by quite unlike curves. With regard to the 

 direct water supply of these insects it must be remembered 

 that they drink dew only, which is at least not noticeably de- 

 ficient over our sand regions as compared with prairie soils. 

 The third consideration also, that of temperature, presents only 

 vague possibilities which seem insufficient to limit the local 



