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THE AMERICAN NATURALIST [Vol. XLIII 



graphically represented, as the expression of a definite 

 difference of physiological activity, as shaped by hered- 

 ity, in relation to that particular factor. Very little, as 

 far as I am aware, has yet been accomplished in this 

 direction, but it is a way that is wide open, and one that 

 should attract those real investigators who, knowing 

 difficulties, do not shrink from them. 



We have considered in a way far from exhaustive 

 some of the problems which specially interest the student 

 of desert ecology, but which in their broader relations 

 are not confined within geographical limits. In the ef- 

 forts now being directed towards their solution the 

 trend, as it appears to the writer, is not so much away 

 from any previous form of thought or method as towards 

 the wise and persistent use of every means that promises 

 results. Progress is certainly being made in the direc- 

 tion of greater exactness; we are learning something of 

 the possibilities of well-directed cooperation; and in 

 these and other ways in which " science returns to the 

 obvious"— to use the apt words of Francis Darwin— is 

 an encouraging promise for the future. 



