14 DROUGHT EESISTANCE OF OLIVE IN SOUTHWESTEBN STATES. 



usually where the outer stems had formed a sufficient barrier against 

 the stock that the central ones had attained an adequate growth to 

 enable them to resist attack. Man}^ of these have reached a height 

 of 12 to 15 feet, and a few exceptionally strong specimens are 18 to 

 20 feet high. (See PI. I, fig. 1.) 



The foliage is a dark, luxuriant green, and vigorous new growth is 

 being made, even on those trees that have been most severely cropped 

 back by cattle. The whole plantation is a notable landmark on the 

 desert plain and can be seen for a long distance. In fact, unculti- 

 vated and abandoned to struggle for itself, the olive has made a 

 winning fight in fair competition with the mesquite of the surround- 

 ing desert, even though it has lacked the thorny defense against 

 grazing animals which nature has supplied to the desert tree. 



The uniform distance in setting out this entire plantation was in 

 squares 24 feet apart. This would prove to be rather too close 

 planting even in an orchard having an abundant supply of water, 

 but where the supply is as scant as this plain affords experience has 

 shown that this spacing, which provides for 75 trees to the acre, is 

 much too close. The luxuriant growth of a portion of these trees 

 was doubtless made possible by the weakened competition of those 

 closely cropped by stock. The olive tree has the ability to produce 

 a system of shallow roots, fully occupying the ground for a wide 

 radius around each tree. But a few 3 ears are needed for a tree to 

 completely take possession of the soil over a radius of 12 feet, after 

 which the struggle must begin with neighboring trees for the avail- 

 able moisture. 



A detailed study of the roots of a typical tree was made — a tree 

 with a trunk diameter of only 5 inches, enlarged just below the sur- 

 face of the ground into a burl 12 inches in diameter and 14 inches 

 in depth, from which radiated 12 roots from a half inch to 2 inches 

 in diameter. Some of these roots had a length of 12 to 14 feet. So 

 numerous were the branches and small feeding rootlets originating 

 from these roots that the soil from a depth of 2 or 3 inches to more 

 than a foot was filled with them. 



The description of "Olive root systems" in this bulletin will afford 

 details applicable to all of these plantations. 



At the remote areas penetrated by branches from the large roots 

 the ground was contested by feeding roots from the adjacent trees, 

 so that it was hardly possible to turn up a shovelful of earth in the 

 orchard without finding evidence of this reaching out for moisture. 

 Yet there was no taproot and no penetrating to great depths for 

 water, as is so characteristic of the mesquite, which had been the 

 natural occupant of this land. It was a most complete and perfect 

 system for appropriating the moisture in the first 15 or 18 inches of 

 the soil, just that which would be penetrated by the normal rainfall. 



192 



