176 Journal of Agricultural Research voi.xx,No. 3 



We have analyzed different portions of orange and lemon trees affected 

 with mottle-leaf, as well as grapefruit leaves and samples representing 

 different degrees of mottling. Most of the samples were collected from 

 the fertilizer plots of the Citrus Experiment Station. In all cases the 

 leaves were collected from shoots 6 or more months of age. The analysis 

 of orange leaves in an advanced stage of mottling is presented in Tables 

 VIII and IX. 



Comparison of the data with the previously submitted analyses shows 

 at once that the composition of mottled leaves differs considerably 

 from that of average mature normal leaves. The principal differences 

 are found in the greater percentages of potassium and phosphate, on 

 the one hand, and the lesser percentages of calcium on the other. The 

 ash of mottled leaves also contains greater percentages of magnesium 

 and sulphate, while the iron, silica, sodium, and chlorin do not differ 

 materially. 



Considerable variations will also be noted among the different samples 

 of mottled leaves. This is probably due to the varying degrees of 

 mottling represented by the samples. However, every sample of 

 mottled leaves that has been analyzed in this laboratory has been found 

 to vary from the normal in the same general direction. 



The average content of water in mottled leaves was found to be 

 slightly higher than in normal leaves and the ash content somewhat 

 lower. Considering the dry matter, the most pronounced differences 

 are found in the lesser calcium content, on the one hand, and the abnor- 

 mally high percentages of potassium and phosphorus in mottled leaves, 

 on the other. The average nitrogen content of mottled leaves is also 

 considerably above normal, as was previously pointed out by McBeth (//). 



From his analyses of normal and mottled citrus leaves, Jensen (7) 

 failed to find any consistent difference in composition. In order to 

 insure uniformity in the age of his samples, he collected the leaves from 

 the current season's growth. On the dates two of his samples were 

 collected, April 18 and May 11, the current season's growth is probably 

 never mature at Riverside. Furthermore, the calcium content, which 

 he reported, was very much below that of any mature normal orange 

 leaf we have been able to find. It seems safe to conclude, therefore, that 

 Jensen's studies were made with immature leaves. It is possible, of 

 course, that the variations in composition incident to mottling may 

 not occur until after the leaves have reached a certain stage of growth, 

 although recent analysis of a sample of leaves about 10 days of age, 

 taken from severely mottled trees, indicates that the composition may 

 begin to diverge from the normal at a very early period. 



It is well known that, with the exception of severe cases of mottle-leaf, 

 the discoloration ordinarily does not become apparent until the leaves 

 have reached an age of 2 to 3 months. Subsequently, the degree of 

 discoloration becomes increasingly intense until the period of normal 



