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THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 



of the trees and may compare the years of rapid growth with those of slow growth, using 

 the two groups that we have already employed in our study of the conservation factor. 

 (C) Again we may combine growth and rainfall, and compare two groups of years, in one 

 of which both the rate of growth and the rainfall increase in amount, and in the other of 

 which both ciuantities decrease. (D) And finally we may combine growth and rainfall in 

 still another way, forming two groups of years in one of which both the rainfall and the 

 rate of growth are above the normal and in the other of which both are below the normal. 



