AREA OF POSSIBLE DRY-LAND OLIVE CULTURE. 37 



AREA LIMITED BY HEAT REQUIREMENTS. 



While the Pope ohve grove has been studied as a case of survival 

 without fruiting in spite of extreme adverse conditions, yet in the 

 garden of Dr. Wellwood Murray at Palm Springs Hotel, with an 

 ample shelter belt of trees around the border, two trees. of the Pendu- 

 lina variety have made a good growth and ripen fair crops of fruit 

 with only scant irrigation, though there is scarcely a summer when 

 a temperature of 120° to 122° F. is not recorded. 



As to the maximum temperature which the olive will withstand, it 

 is hard to find a locality in the United States where a fair degree of 

 success may not be met with. 



Contrary to the often-expressed opinion that it is only successfully 

 grown in regions adjacent to the seacoast " the olive thrives and 

 produces abundantly in such hot interior locahties as Biskra, Algeria; 

 Fresno, Cal.; and Phoenix, Ariz. 



At Phoenix, Ariz., maximum summer temperatures of 112° to 116° 

 F. are matters of record, with a July mean of 90° F. The mean 

 temperatures for the months of June, July, August, and September 

 are 6 to 9 degrees higher than those of Catania, the warmest olive- 

 growing station of Italy,* and compare quite closely throughout the 

 year with the mean of Biskra, Algeria. (See fig. 10.) 



There is near Phoenix a small but flourishing olive industry under 

 irrigation, the trees making a rapid, healthy growth and bearing good 

 crops of olives, yielding oil of an excellent quality. This affords 

 proof of the high temperature which the olive will sustain when that 

 factor alone is taken into account. 



There is an area through the more wind-exposed portions of the 

 Colorado Desert where it is possible that the hot, dry winds of the 

 early spring prevent, as a rule, the setting of the fruit, though the few 

 trees to be found there make a fair growth with a minimum of 

 irrigation. 



For the development of the olive fruit a rather constant number of 

 heat units above the dormant or zero point of the olive tree is needed 

 during the active or growing season. For convenience in transcrib- 

 ing the data from weather records, however, these heat units are here 

 assumed in degrees above zero, Fahrenheit. Thus, as the mean tem- 

 perature of Phoenix, Ariz., has been determined after a number of 

 years of recorded observations to be 52° F. for the month of January, 

 multiplying 52 by 31, the number of days, gives 1,612, representing 

 the number of heat units for that month. Computing each month 

 in the same manner, their sum amounts to 25,607, the number of 

 heat units for the year. 



tt Caruso, G. Dell' Olivo, Turin, 1883, p. 34. 

 192 



