OLIVE BOOT SYSTEMS. 27 



the ascendancy in water appropriation it will sooner or later have 

 three or four adjacent trees in the suppressed class. This suppression 

 of the weak trees by the stronger rooted dominant ones begins as soon 

 as the roots meet in the intermediate territory, which has happened 

 in many instances in this grove and seems to account for the death of 

 many of these trees and the weak condition of others. This affords 

 conclusive proof that olive trees can not be grown successfully 2 1 feet 

 apart under light rainfall without ample irrigation, and, what is more 

 significant, that when given wide planting they are capable of extend- 

 ing their root systems and collecting their water supply from a very 

 wide area. 



OLIVE ROOT SYSTEMS ADAPTED TO UTILIZE LIMITED RAINFALL. 



The remarkable endurance of drought displayed by the olive trees 

 of which an account is given in this paper, but especially by those at 

 Palm Springs, Cal., must be explained (1) by unusual ability to collect 

 moisture from a soil supply normally deficient and (2) by an ability 

 to conserve that moisture and perform their physiological work on a 

 supply that would prove totally insufficient for ordinary trees. For 

 the first we must look to the roots, and as these were uncovered and 

 plotted it became evident that the deeply penetrating system pos- 

 sessed by the mesquite for bringing up water from a subterranean 

 source was not possessed by the olive, nor would it have availed much, 

 as on near-by land a well had been sunk to a depth of 80 feet, disclos- 

 ing only dry cobblestone and gravel. No penetrating taproots were 

 found, but usually each tree had a deeply-seated burl or swelling two 

 or three times the diameter of the trunk above ground, from which 

 radiated evenly in all directions a strong set of roots running off nearly 

 horizontally. Plate IV, figure 1, shows the trunk, burl, and main 

 roots of a tree which was selected for study from the most resistant 

 variety of the Pope plantation. 



This tree was barely 6 feet in height, with a top spread of 7 feet and 

 a trunk diameter of 3f inches ; yet we find a root system radiating to 

 10 and 1 1 feet in nearly all directions and having a total length of 

 roots of one-eighth of an inch in diameter and upward of about 185 

 feet. The length of roots was at least double that of the twigs and 

 branches of similar diameter, while the area occupied by the roots was 

 nine thnes that of the spread of the branches. 



The strongly gnarled burl was a foot in depth, and from this the roots 

 issue at depths of 2 to 10 inches. With but a few exceptions they 

 all break up into fine rootlets at depths of 5 to 8 inches, the greatest 

 number being at 6 inches. In two cases small laterals penetrate to 

 18 inches in depth, and there was a curious case of branches from 

 two separate roots going down at the same ])oint — possibly an old 

 burrow of some rodent affording a more mellow soil — to 3G and 42 



192 



