NOTES ON ROOT VARIATION IN SOME DESERT 



PLANTS 



W. A. CANNON 



The Desert Laboratory, Tucson, Arizona 



As observations on the roots of the larger plants are extended 

 it is becoming more and more apparent that the root-systems of 

 perennials growing under natural conditions in arid, or semi- 

 arid regions, have capacities for variation which are character- 

 istic of the species, or genera, and may also be of significance to 

 the plant in its survival as well as in a variety of other vital 

 phenomena. It is also true, however, as will be shown in this 

 paper, that in nature the limit of root variation, in such instances 

 as have been studied, may not be attained. Whatever may be 

 the bearing of this fact on distributional problems, it at least 

 is noteworthy. 



The observations reported in the present paper are along three 

 lines. They are, in the first place, on plants which are under 

 wholly normal and natural conditions, in the second place, they 

 touch cultures in an out-door experimental plot, and, finally, 

 they concern the behavior of certain species when grown under 

 special experimental conditions, partly in the greenhouse and 

 partly out of doors. 



VARIATIONS UNDER NATURAL CONDITIONS 



Observations show that certain types of roots exhibit in nature 

 a wide range in variation, which may hold an intimate relation 

 to the pressure of the soil environment, while, at the same time, 

 roots of other sorts may show but little deviation from type 

 although the environment may change. These points may be 

 illustrated briefly. Plants possessing a pronounced tap root, 

 such as Koeberlinia and Zizyphus, occur only ■ where there is 

 much earth room, since their roots are incapable of great varia- 



323 



THE PLANT WORLD, VOL. 16, NO. 12, DECE-MBEK, 1913 



