9 o THE POPULAR SCIENCE MONTHLY 



SOME FEATURES OF THE EOOT-SYSTEMS OF THE 



DESERT PLANTS 



By Dr. W. A. CANNON 



DESERT LABORATORY 



THE roots of the desert plants are of interest, in part because of 

 their relation to the physiological activities of the shoot, and in 

 part because of their own physiology. There is a close relation between 

 the character of the roots of the desert plants and the distribution of 

 the plants, and probably with many other activities of the plants, as, 

 for example, the formation of the leaves, of the flowers and the taking 

 on of new growth. What the precise relation may be between the root- 

 systems and the adaptation of desert plants to desert surroundings is 

 not known, nor, for that matter, the relation of the roots of the plants 

 of the more humid regions to their distribution, or to their origin. 

 Also the special relation of the roots of plants to the substratum has not 

 been extensively investigated, as, for example, the character of root 

 development as related to the precise per cent, of water content, or to 

 the temperature. The lack of quantitative experimental studies on 

 roots in soil is to be attributed in large part to the difficulty in studying 

 the soils. If certain activities of the roots, or the significance of root 

 character to many features of the plants' activities, are to be under- 

 stood, it will be necessary to do quantitative experimental work on 

 plants growing in the soil, and not, as heretofore extensively done, 

 growing under highly artificial conditions. 



It is popularly supposed that the roots of the desert plants are very 

 long — that is, that they penetrate the ground to great depths, and from 

 this that the length of a root-system is in some way a measure of the 

 aridity of a locality. It is difficult to say how this idea arose, which 

 really is without adequate foundation, because a relatively small amount 

 of work has been done on the roots of the plants either of the humid 

 regions or of the deserts, in the field. It is probable, however, that the 

 few excavations that have been made have been carried on in those 

 places where it chanced that the roots penetrated to great depth. But 

 it is in exactly these places where the most favorable moisture conditions 

 of the given locality are to be found, namely, where the soil is deep, 

 giving an opportunity for the penetration of water to a great depth, as 

 in the bottoms, or along the banks of stream ways — arroyas in our 

 southwest, ouedes in southern Algeria, or weds in the eastern Sahara. 



