EXAMPLES OF DROUGHT RESISTANCE. 15 



The soil, greatly deficient in humus, contains clay enough to make 

 it very hard when dry, and the tramping of grazing stock still further 

 compacted the surface, preventing the ready absorbing of water 

 when a rainfall came. Application of the now well-known principles 

 of thorough cultivation and light furrowing across the slope to secure 

 water storage and the retarding of evaporation by a dust mulch 

 would have aided these trees greatly in utilizing the rain which fell. 



DRY-LAND OLIVE GROVE NEAR FLORENCE, ARIZ. 



Not far from the Casa Grande and Florence road, in the valley of 

 the Gila River and about 5 miles southwest of Florence (see map, 

 fig. 1), a ranch was developed and a plantation of olives and other 

 fruits was made, probabl}^ at about the same time as that at Casa 

 Grande. An area of about 8 acres was set in olives, the trees being 

 arranged in squares 20 feet apart each way. This tract has been 

 kept securely fenced, so that no damage from live stock has occurred. 

 From the scant information that can be gathered these trees have 

 received no irrigation for six years. 



The soil is a much stiffer clay than that at Casa Grande. A well 

 near the orchard, now caved in, shows no water for a depth of more 

 than 40 feet. An inspection of this grove shows that while possibly 

 5 per cent of the original setting of trees failed to grow, but a very 

 few died later. The average height of these trees is about 20 feet. 

 A majority of them grow in the form of stools, sending out several 

 minor stems from near the ground. Some single trunks from 8 to 

 12 inches in diameter were noted. The formation of a much en- 

 larged burl at the surface of the ground was a very common feature. 



A most significant fact was that the trees around the borders of 

 the grove were much larger and of more vigorous and healthy growth 

 than those where there was a perfect stand in the interior. While 

 few of the interior trees are dying, the scantier and less healthy foliage 

 and more slender growth of the branches all testify to the severity 

 of the struggle for moisture which is taking place. (See PI. II, fig. 2.) 



No systematic study of the root development was made, but a 

 number of holes dug in various parts of the grove showed that, as in 

 the Casa Grande grove, the extent of roots was such as to occuj^y 

 the entire area, fine rootlets being disclosed wherever the soil was 

 turned. Even where missing trees gave a diagonal distance of more 

 than 45 feet between those standing, the roots hatl extended so as to 

 occupy this space. 



A most significant fact concerning this planting is shown in Plate 



II, from photographs taken in March, 1909. A blo(^k of about 3 



acres of apricots and almonds ])lanted by the side of the olives is 



shown in Plate II, figure 1, on the left. The trees had made an 



57054°— Bui. 192—11 2 



