No. 568] SHORTER ARTICLES AND DISCUS SI OX 251 



approximately agree in such limitation they are said to occupy 

 the same life zone. 



The observation of this category of distributional delimita- 

 tion is particularly easy in an area of great altitudinal diversity 

 like that comprised in the southwestern United States. The 

 writer is led to wonder if those authors who minimize the impor- 

 tance of temperature have ever been privileged to travel exten- 

 sively, and carry on field studies, outside of the relatively uni- 

 form eastern half of North America ! 



Study of any area which varies widely in altitude and hence 

 provides readily appreciable differences in daily temperature 

 from place to place brings conviction of the very great effective- 

 ness of temperature in delimiting the ranges of nearly all species 

 of animals as well as of plants. Particular attention may be 

 called to the pertinent results of Merriam's survey of Mount 

 Shasta. 



But temperature is not to be considered the only delimiting 

 factor of environment, though its possible overemphasis by the 

 Merriam school seems to have led some other persons to believe 

 that this view is held. In fact it becomes evident, after a con- 

 sideration of appropriate data, that very many species are kept 

 within ideographic bounds in certain directions only by an in- 

 creasing or decreasing degree of atmospheric humidity. By 

 plotting the ranges of many animals as well as of plants coin- 

 cidence in this regard is found in so many cases as to warrant, 

 the recognition of a number of "faunal areas" — on the causa- 

 tive basis of relative uniformity in humidity. It is probable that 

 every species is affected by both orders of geographic control. 



The reader may enquire as to the grounds for employing the 

 widely used terms zone and fauna in the restricted sense here 

 prescribed. In reply, it may be said that this is not an inno- 

 vation, but is an adoption of a usage which has come about his- 

 torically among a certain group of workers in the geography of 

 vertebrate animals in North America. The writer recognizes the 

 fault in imposing restricted meanings upon old terms, but he 

 also hesitates at coining new words. 



As to which is the man important, assembled data seem to 

 show that more genera and higher groups are delimited by zonal 

 boundaries than by faunal boundaries. The arresting power of 

 temperature barriers would therefore seem to be relatively the 

 greater. 



