42 University of California Publications in Agricultural Sciences [Vol. 3 



ing, with the temperature at 62 F. and the humidity 54%, the water 

 content of similar leaves was found to be 172.6%, showing a differ- 

 ence of 28.3%. This phenomenon is taken to indicate the presence of 

 incipient drying in citrus and is in full accord with the results of 

 the writers above mentioned as well as with those obtained by Lloyd. 



Since the young fruits have a higher water content than adjoin- 

 ing leaves which, in turn, exhibit a diurnal decrease in relative water 

 content, the conclusion, a priori, that the leaves might possibly draw 

 on the water supply of the fruit during periods of excessive transpira- 

 tion seemed entirely plausible. If such is the case it would seem that 

 leaves so favorably situated should not show this daily variation, at 

 least to the degree shown in the leaves not so favorably situated. The 

 data in table 1 show, however, that the average difference in water 

 content of the two sorts of leaves gathered in the forenoon and after- 

 noon is quite small. This is taken to indicate that if such leaves do 

 utilize the water supply of the fruits, the evaporating power of the 

 atmosphere is so strong that as fast as they receive this surplus water, 

 it is lost and thus causes no appreciable difference in their relative 

 water content. 



The next step was to ascertain the water content of different kinds 

 of fruits, those destined to remain and mature, and those showing 

 indications of subsequent abscission. It is quite easy to distinguish 

 between the two, from a week to ten days before abscission occurs, 

 by the difference in their appearance. Exposed fruits destined to 

 drop exhibit a small yellow spot about the navel end several weeks 

 before the actual drop occurs. This spot gradually extends and 

 spreads until at abscission it usually occupies at least half the area 

 of the fruit. In the case of well-shaded fruits, the yellow color is 

 evenly distributed over the entire surface. A large number of mois- 

 ture determinations were made which showed that those fruits destined 

 to subsequent abscission averaged 59% less water than those fruits 

 destined to remain and mature. (See table 1.) The presence of this 

 condition in the fruits, especially when considered in connection with 

 the daily increase at certain hours in the water deficit of the leaves 

 immediately behind them, seems to point to the possibility of the leaves 

 depriving the fruit of a part of their normal water supply. It cer- 

 tainly indicates an abnormal water relation. 



Lemon growers prune their trees at all seasons of the year, even 

 while the fruit is still on the trees. It is a well established practice to 

 gather the good fruit from the excised branches immediately, in order 

 to prevent it from becoming flaccid. Inasmuch as the fruit, as ordi- 



