PLANTS IN ARID REGIONS—SPALDING. 463 
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 efforts now being directed toward their solution the 
trend, as it appears to the writer, is not so much away from any 
previous form of thought or method as toward the wise and persist- 
ent use of every means that promises results. Progress is certainly 
being made in the direction 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. 
