24 THE FUTURE OF ARID LANDS 
about one-third of the land surface. Here is an experiment already 
planned and carried out. All we have to do to advance our knowl- 
edge in the field of the more complete utilization of these arid 
lands is to study and interpret properly what nature has already 
accomplished. Here is a great field for the physiologists. Here also 
is a rich resource for genetic exploration and the geneticist can be 
well guided by the physiologist as to the means by which plants 
and animals can be better adjusted to this rather extreme environ- 
ment. Can the geneticist breed an animal that can live on meta- 
bolic water or can concentrate the urea in the urine, or can he 
produce a maize plant with only one seed root and with an elon- 
gated hypocotyl? Nature has pointed the way. 
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2. Briggs, L. J., and H. L. Shantz. 1912. The wilting coefficient for 
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3. Burr, W. W. 1914. The storage and use of soil moisture. Neb. Agr. 
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Wasserdampf und deren Bedeutung ftir die Pflanzen. Zweiter Be- 
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