DISTRIBUTION AND ADJUSTMENT 



95 



it substantiated by many commonplace facts. Thus we name 

 many insects by the time of their appearance, as May flies, 

 June beetles, the fall army worm, etc. Just as the appearance 

 of the robins and the bluebirds marks early spring, so we think 



,V 20- 60% 



::: eo- 8o% 



Fig. 57. — Map showing relation of rainfall to evaporation in Eastern United 

 States. Unmarked lower left, rainfall 20 per cent or less of the evaporation. 

 The other markings are explained on the figure. 



of midsummer as butterfly time, and the chirp of the cricket as 

 the first voice of fall. 



In the local place distribution of plants, moisture is of prime 

 importance, or rather the ratio between rainfall and evaporation. 

 If the water supply greatly exceeds the evaporation, then the 

 plant grows in a pond or marsh and is designated a hydrophyte. 



