REACTIONS OF CERTAIN MOIST FOREST MAMMALS. 185 



the evaporating power of the air is the best index of environmental 

 conditions of the white-footed woodland mouse as well as other 

 land mammals seems evident. 



This mouse is primarily a ground stratum animal and since 

 relative humidity decreases from the ground upward one would 

 expect the reactions of such a species to be more pronounced 

 than those from the higher strata, and Shelford ('13) from a series 

 of experiments found (i) animals react to air of a given rate of 

 evaporation whether the rate of evaporation is due to moisture, 

 temperature, or rate of movement; (2) the sign and degree of the 

 reaction to the given rate of evaporation are in accord with the 

 comparative rates of evaporation in the habitats from which the 

 animals were collected though the reaction to evaporation 

 due to temperature was usually sharper; (3) the animals of a 

 given habitat are in general agreement in the matter and sign 

 of the reaction; the minor differences which occur are related to 

 vertical conditions and kind of integument; (4) there is a rough 

 agreement between survival of time in an air of high evaporating 

 power and kind of integument, but no agreement between 

 survival of time and habitat when a number of species of the 

 community are taken together. 



Fuller ('n) and McNutt and Fuller ('12) made a comparative 

 study of rates of evaporation in different kinds of forests in north- 

 ern Illinois. Their figures show that the rate of evaporation 

 was dependent upon the kind of forest and the following results 

 were obtained. Taking 100 as a relative evaporation scale: 

 Cotton wood dunes, 260 per cent.; oak dune, 127 per cent.; 

 oak hickory, 115 per cent.; maple beach forest, 100 per cent. 

 Shimek ('10, 'n) made observations on the relative rate of 

 evaporation on the prairies of western Iowa, and his results show 

 that the rate of evaporation is much greater in exposed places 

 than w r here there is shelter from the sun and wind. The mice 

 apparently avoid higher rates of evaporation by staying in the 

 forest. 



III. EXPERIMENTAL STUDY OF THE RELATION OF ENVIRONMEN- 

 TAL FACTORS OF DISTRIBUTION. 



Aron ('ii), Rheinhard ('69) and Rubner ('90) have shown that 

 evaporation directly affects the physiological processes of certain 



