332 THE FUTURE OF ARID LANDS 
Consideration of better use of such land is gaining more interest 
by certain international and governmental organizations as well as 
by many scientific bodies and institutions. 
Most of the efforts for improvement of arid zones have been 
directed at studying the plant side. Search has been made for 
adapted species, methods of planting have been developed, and 
considerable areas have been reseeded. Although animals were 
responsible for aridity, less effort was devoted to studying grazing 
management. Moreover, less attention has been given to the 
human factor which often is the real cause of the lack of balance 
between the fodder reserves and the misuse of the grazing lands. 
Studies of all phases of the problem must go hand in hand if we are 
to find a solution. 
Plants and animals adapted to any given arid environment will 
differ from place to place. To obtain maximum productivity in 
arid zones we have to use the best adapted animals that can graze 
drought-resistant plants. The range should be kept in a state of 
productivity to be used by the present and future generations. 
For the selection of plants and animals better suited to arid 
zones, a thorough understanding of the ecological, genetic, and 
physiological basis for drought resistancy has to be borne in mind. 
Ecologists are mainly interested in adaptation to external 
environments. Physiologists are primarily concerned with equilib- 
rium of functions within the organism. Geneticists are concerned 
with the hereditary makeup of the organism. Range technicians 
must make use of the relation of all these factors to one another. 
Drought-resistant perennial plants are equipped with morpho- 
logical and physiological characters that enable them to withstand 
drought. The most important of these are: (1) deep penetration 
and extensive development of the root system, (2) relatively high 
osmotic pressure of the cell sap, and (3) higher capacity for regu- 
lating transpiration (g). 
Certain annual plants can complete their life cycle in a com- 
paratively short time, thus avoiding, rather than withstanding 
drought. This subject is dealt with by Shantz. 
Animals adapted to arid zones are the result of interaction of 
two main factors, namely heredity and environment. Under arid 
