386 



ENVIRONMENTAL CONDITIONS. 



C. COMBINATIONS OF TEMPERATURE AND MOISTURE CONDITIONS. 



It has been pointed out that temperature indices show a zonation 

 of the country, the zones extending generally west and east. A similar 

 generalization may be stated for the moisture indices that we have 

 studied, only the direction of the isoclimatic lines is generally north and 

 south in this case. Of course these statements are true only in a general 

 way; what is most worthy of emphasis is that the two kinds of zones 

 tend to cross each other, so that if our area had been large enough we 

 should have had 4 moisture provinces within each temperature prov- 

 ince and 5 temperature provinces within each moisture province. 

 This observation has suggested the cartographical combination of 

 moisture and temperature indices, by which the country becomes a 

 mosaic of irregularly shaped areas representing 34 temperate moisture- 

 temperature provinces. Since such combination charts bid fair to be 

 very largely used in climatological ecology, the descriptive names of 

 these various provinces, as we have suggested them, may be tabulated 

 here for convenience. 



Livingston's moisture-temperature products receive attention, but, 

 w^hile they promise to be of value in some ways, as, for example, in the 

 comparative evaluation of land in different parts of the country, their 

 very nature precludes their being of very great general service in the 

 etiological study of plant distribution. They refer to the efficiency 

 of the climatic complex for plant growth in general rather than to its 

 efficiency for any particular species or kind of vegetation. 



