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



could be found in any part of the shoot. Samples of leaves for mois- 

 ture content determination were taken at 8 :30 A.M. Although remain- 

 ing in the shade the leaves showed at 12 :15 P.M. distinct evidence of 

 wilting and upon examination, eosin staining was found in the petioles 

 of every leaf on the shoot, with the exception of a few on the extremi- 

 ties of the side branches. At 12:30 P.M. samples were taken for 

 moisture determination. 



TABLE 5 



MOISTURE CONTENT OF LEAVES TO WHICH WATER WAS AVAILABLE FROM 



Two SOURCES 



Weight of container Weight of same Weight of mate- Average water 



and material in when dry in rial in grams content in 



Hour picked grams grams per cent 



8:30 A.M. 21.967 21.617 .562 



23.455 23.162 .480 160.8 



12:30 P.M. 21.914 21.659 .459 



21.552 21.345 .382 121.6 



The data obtained in this experiment show that during the night, 

 when the draught of the atmosphere on the water supply was low, the 

 leaves were able to maintain themselves in a normal condition by 

 using water from the base container. This is evidenced by the normal 

 water content of the leaves in the morning, as well as indicated by the 

 fact that no eosin whatever was drawn back, although the vascular 

 bundles were open to* its entrance. However, as the atmospheric 

 evaporating power increased during the forenoon, it became more and 

 more difficult for the leaves to obtain requisite amounts of water 

 through the conducting system in the normal way. At a point near 

 12 M. the leaves became unable to obtain enough water in this fashion 

 and they began to draw on the aqueous solution of eosin. The shoot 

 was now drawing water from both ends to satisfy the demands of the 

 transpiring leaves. But the atmospheric pull for water became so 

 severe that even this double supply did not suffice to maintain the 

 water content of the leaves at normal. The water deficit began to 

 increase and continued until a condition of actual wilting resulted. 

 Between 8:30 A.M. and 12:30 P.M. the leaves decreased in water con- 

 tent by 39.2%, although both ends of the shoot were immersed in 

 water. 



From the evidence above presented it seems clear that under con- 

 ditions favorable to rapid transpiration it is entirely possible for the 

 leaves of citrus trees, at least, to draw water back from the young 

 fruits. Moisture determinations of fruits under such conditions 

 showed a considerable decrease in water content and indicated that 



