Frost and the Prevention of Damage by It. 



41 



radiation from the fruit so that the fall in temperature inside the 

 fruit lags considerably behind that of the air. 



MM. 2A.M. 3AM 4AM. 5AM. 6A.M. 7A.M. 



7//t/ 8PM. 



/0PM. //PM. 



4O 



\ 



4/r temperature 



Sf/e/fer 

 0ra/?gre 



30 

 28' 



85* 



\ 



X7 



FIG. 16. Eye readings of the temperature inside a 3J-inch mature navel orange on the 

 tree exposed to the sky, compared with simultaneous readings of the air temperature 

 Inside a standard thermometer shelter at the same height above the ground. Xote that 

 the temperature inside the fruit did not fall below 28, which is approximately the 

 freezing point of the juice. 



The critical temperature for nearly ripe oranges is most often 

 given as 26 F. to 27 F. During the winter of 1918-19, however, 

 two navel orange groves in southern California experienced air 

 temperatures on different nights as shown in figure 17. 



Comparative figures on the amount of damage in the two groves 

 are given below : 



Comparison of damage to two groves. 



1 Fruit with up to 15 per cent of tissue 15 per cent frozen marketed in this grade, which brought from 

 40 to 70 per cent of the price received for undamaged fruit. 

 4 Includes misshapen fruit, frozen fruit, etc., total loss. 

 3 More than 15 per cent of tissue 15 per cent frozen. This fruit is a total loss. 



The fruit in grove Xo. 2 was of a much better quality before the 

 first frost than that in grove Xo. 1, which accounts for the large 

 amount of culls, not frozen, in grove No. 1. If there had .been no 

 damage from frost the amount of fruit marketed as " extra choice " 

 and " choice " would have been much larger in grove Xo. 2 than in 

 grove Xo. 1. 



Green oranges are injured at considerably higher temperatures, 

 their critical temperature being between 28 F. and 29 F. 



