1 84 



Journal of Agricultural Research 



Vol. XX, No. 3 



The results show that the sap of Valencia orange leaves at the age of 

 6 weeks contains smaller amounts of dissolved solids and total ash ma- 

 terial than mature leaves. The calcium content increases more than two- 

 fold, and the potassium and phosphorus content decreases in passing to 

 maturity. On the other hand, the sap of mottled leaves has a higher 

 specific gravity and a higher ash content than that of mature normal 

 leaves. The calcium content, however, is considerably less, while the 

 potassium and phosphorus content is much higher. 



It is evident from these data, therefore, that the sap of mottled Valen- 

 cia orange leaves is materially different from that of normal leaves, 

 either when they are 6 weeks of age or mature. 



The water-soluble constituents were found to diverge in the same 

 general direction as the sap. It is interesting to note that a very high 

 percentage of the potassium, phosphorus, and calcium of orange leaves 

 is soluble in water. 



Samples of fully mature normal leaves and of severely mottled leaves 

 of the previous year's growth were collected from Navel orange trees of 

 the fertilizer plots at Riverside in August, 1918. The sap was expressed 

 and used for more complete chemical study. (Tables XIX and XX.) 



Table XVIII. — Composition of mottled Valencia leaves 



<» Expressed in terms of dry matter. 



The results are fairly concordant with those reported above for Valencia 

 leaves. It is again shown that the composition of the sap of mottled 

 orange leaves differs widely from that of normal leaves. The data also 

 show that the ash of the sap of each sample contained considerably 

 smaller percentages of calcium and higher percentages of iron than 

 those reported above for the ash of the leaf as a whole, while the per- 

 centages of the other constituents are not materially different from 

 those of the entire leaf. The calcium content of the sap of Navel 

 orange leaves appears to be lower than that of Valencia leaves. (Com- 

 pare Tables XVII and XX.) 



Upon studying the preceding data, it seems difficult to escape the con- 

 clusion that there must be some important physiological significance 

 attached to the fact that the sap of mottled orange leaves contains only 

 about one-half as much calcium and approximately twice as much 

 potassium and nitrogen and three times as much phosphorus as normal 

 leaves. 



