THE GRASSLAND CLIMAX. 117 



SUBCLIMAX PRAIRIE TRUE PRAIRIE 



6 



5 

 4 

 3 

 2 



1 







MIXED PRAIRIE 



BUNCH GRASS PRAIRIE 



The Dalles, Oregon 



17 in. 



n 



ii 



Fresno, California 



10 in. 



it" 



SHORT GRASS TL-AINS 



DESERT PLAINS 



Oracle, Arizona 



17 in. 



Ill 



ll 



Fig. 3. — Monthly and total rainfall for representative localities in the various 

 associations of the grassland climax. 



As a botanist, Transeau properly emphasized the water relations, employing 

 the percentages found by dividing the mean annual rainfall by the depth of 

 evaporation. The unavoidable errors due to the imperfection of the record 

 (Livingston, 1913 : 272) are so great, however, that his results only served to 

 emphasize the well-known fact that in North America forest yields to prairie, 

 prairie to plains, and plains to desert from east to west, as rainfall decreases 

 and evaporation increases. Probably the author did not intend that his 

 climatic lines should be taken for the limits of vegetation units, but such an 

 outcome was unavoidable. In referring to Transeau's work, Waller (1918 : 49, 

 59) says: 



