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University of California Publications in Agricultural Sciences [Vol. 3 



over its water loss. This coudition itself eou.stitutes strong evidcnoe 

 of its tropical origin. 



If there be any regulatory action upon transpiration it should be 

 brought out in a study of the transpiration curve as compared to the 

 evaporation curve. These two curves for a typical day in July are 

 shown in figure 9, and it will be seen that the general form is very 

 similar and that the maxima of the two were reached at the same 



4 p. M. JULY 



12 p. .M 



JULY 



12 .M. 



Fig. 9. Comparison of Citrus transpiration curves witli the evaporation 

 curve for the same period. Nos. 1, 2, 3, and 4 are transpiration curves obtained 

 bv the potometer method. No. 5 is the evaporation curve obtained from a 

 Livingston white cyliBdrical porous cup atmometer. Ordinates represent water 

 loss in cc; abscissae, hours of the day. 



period. "Were there any regulatory action the transpiration curve 

 should reach its maximum some time before the evaporation curve. 



Susceptibility of Citrus Varieties to Abscission 



It is well Imown that when grown under similar conditions the 

 Valencia variety of orange and the pomelo do not shed the young 

 fruits in anything like the same proportion as the Washington Navel. 



