EXAMPLES OF DROUGHT RESISTANCE. 23 



this Palm Springs soil in a very marked way from that of the Casa 

 Grande. Both are in striking contrast with samples from the dry- 

 land olive district of Sfax, in northern Africa, described in Mr. 

 Kearney's bulletin previously referred to. The much higher per- 

 centage of clay in the Sfax samples gives a very distinct character to 

 that soil, which as it exists in nature impresses one as sandy, owing 

 doubtless to the clay and silt particles being cemented together. 



In chemical composition these soils (Table V") show a striking 

 similarity in the lime content, having only one-eighth to one-fourth 

 as much of that element as is found at Sfax. 



In the amount of potash the Casa Grande and Palm Springs sam- 

 ples are also very much alike, being five to ten times richer than the 

 Sfax samples. In the amount of phosphoric acid it is interesting to 

 note that the Palm Springs soil, though seemingly a desert sand, 

 contains more than twice as much of this important element as is 

 found in the Casa Grande samples. In the potash and phosphoric 

 acid contents either of these samples compares favorably with aver- 

 age agricultural soils ; for instance, with the soils of the famous Michi- 

 gan peach belt, ^ while in phosphoric acid the Palm Springs samples, 

 averaging 0.436 per cent for the entire 18 inches in depth, are ahead 

 of all but the very richest farm lands of the eastern United States. 

 This richness of desert soils in phosphoric acid and potash is espe- 

 cially advantageous to olive culture, as investigations by the Cali- 

 fornia Agricultural Experiment Station have shown that the olive 

 makes mucli higher demands upon the soil for these elements than 

 do grapes, plums, apricots, or oranges. •= 



HISTORY OF THE GROVE. 



As nearly as can be gathered the greater part of the Pope olive 

 orchard was set in 1890 and 1891. There was at that time an ade- 

 quate supply of water available from the Whitewater ditch, which 

 was conveyed to each block of land by box conduits. Along these 

 conduits and across the north side of the blocks rows of cottonwood 

 trees were set 20 feet apart. Their influence on the olive plantation 

 will be referred to later. 



The olive trees were planted 21 feet apart on the hexagonal system, 

 giving 116 trees to the acre. For the first seven or eight 3'ears there 

 was a fair supply of water. No Bermuda grass or other serious weed 

 gained a foothold and the work of irrigating the trees was the chief 



a From analyses by Mr. Joseph G. Smith, of the Bureau of Soils, U. S. Dept. of 

 Agriculture. 



6 See Roberts, I. P., "The Fertility of the Land." 



c Report of the Director of the California Agricultural Experiment Station, 1894-95, 

 p. 124. 

 192 



