lOlSl] CoH-Hodfison: Abnormal Shcchlinij of fl'ashington Navel Orange 289 



ening tissue at the base of the ovary may prevent the fall of the fruit. 

 These dead, dry fruits, as shown in plate 31. are often quite conspicuous 

 on the trees. Soon after the application of the stimulus, but several 

 days before actual separation. tli(> larger fruits assume a characteristic 

 appearance, lo.sint; their luster ami taking- on a lighter green color. Tn 

 the ease of exposed fruits the yellow color is deeper around the apex, but 

 this is not the case with shaded fruits. It is thus a simple matter to 

 select any number of fruits which are destined to absciss several days 

 before separation actually occurs. 



Experinicnts carried on in the laboratory and observations made in 

 the field, both in a survey of the citrus districts t)f southern California 

 immediately following the heat wave of Jiuie 15-17, 1917. and at 

 Bakersfield during 1916 and 1917, have shown that the time inter- 

 vening between the application of the stimulus and actual separation 

 is from four to ten days. The shorter periods were obtained in the 

 laboratory, whci-e the room temperature was uniroi-mly high. 0\u' 

 observations are that under field conditions abscission is ordinarily 

 complete within five to eight days after the application of tbe stimulus. 



Normally, orange blossoms, being borne in cymes, open in succession. 

 beginning about JIareh 20 in the San Joa(|uin N'aili'y and i-untinuing 

 about one month. Al)seission varies with the sea.son but usually it is 

 in evidence from April 1 to about July 1. a period of three months. 

 The period of maximum shedding occurs during the latter half of 

 April. It should be noted that the season <if 1917 was uni(|uc in being 

 the latest on record. Protracted cool weather delayed the bloom fully 

 five weeks, with a conseciucnt delay of the period of maximum shedding. 

 A comparison of the mean maximum atmospheric temperatures for the 

 years 1914-17 inclusive is shown in table 2. The comparative lateness 

 of the lf)17 season is app;irent fnnii a stu<ly of this table. 



TABLE 2 



Monthly Me.\n .M.vxi.mum Temperatures for Tex Months at Bakersfield 



Compiled from V. S. Weather Bureau Records 



