330 



W. A. CANNON 



The root-system of 0. versicolor consists of a brush of sup- 

 porting roots, which penetrate to a depth of 20 to 30 cm., and, 

 in addition, radiating absorbing roots, which extend outward for 

 a distance of 2 m., more or less, and He 5 cm., or more, beneath 

 the surface. As in all mature specimens of cacti with tree-like 



Fig. 2. Opuntia arbuscula, from the experimental plot, showing fibrous nature 

 of the roots. 



habit, the bases of the absorbing roots are somewhat thickened 

 and serve as props, aiding the anchoring roots in maintaining 

 the upright position of the plant. 



In the experimental plot the root-system of 0. spinosior con- 

 sisted almost wholly of a brush of anchoring roots extending 



