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



The rates of increase in magnesium and sulphur are also rapid during 

 the early part of the growth period, and each of these constituents con- 

 tinues to accumulate in the leaves up to maturity, but the absolute 

 amounts never become high. Since irregularities occurred in the size 

 of the leaves, it is doubtful whether any important amount of either 

 magnesium or sulphur is translocated to other portions of the tree after 

 maturity has been reached. 



The maximum amounts of potassium, phosphorus, and nitrogen were 

 deposited before the leaves were 6 weeks of age. The rates of increase 

 of each were considerably less than that of calcium. The data show that 

 a considerable portion of these elements migrates away from the leaves 

 after certain periods. With potassium and nitrogen the loss takes place 

 after maturity has been reached, while the phosphorus begins to recede 

 even before maturity is attained. 



Similar data for iron are omitted because of the magnitude of the ana- 

 lytical error involved in its determination. 



Samples representing more frequent intervals in the growth cycle 

 would certainly afford more detailed information regarding absorp- 

 tion. It is possible that the analysis of such samples when plotted 

 might show breaks in the curves not indicated by the existing data. 

 For example, the exact period in the growth cycle when the leaves con- 

 tained the maximum amount of potassium might be shifted to some 

 extent and other fluctuations might also be found. However, other 

 analyses of immature orange leaves at different seasons of the year show 

 a fairly close agreement with those reported above. On the whole, we 

 are inclined to believe that the main features of the composition of the 

 orange leaf have been determined. 



It seems appropriate to emphasize the fact that citrus leaves are ex- 

 tremely calcareous, and much more so than most of the economic plants. 

 As is well known, the ash of some of the legumes contains high percentages 

 of calcium, but relatively few have been reported to contain as high per- 

 centages of calcium as citrus leaves. Not only is the ash of citrus leaves 

 high in calcium but the total ash content is high also. It is unusual to 

 find dried plant material that contains from 5 to 7 per cent calcium. 



COMPOSITION OF MOTTLED ORANGE LEAVES 



The condition of citrus trees known as mottle-leaf has been widely 

 discussed. Much study has already been devoted to it, and several 

 hypotheses have been advanced concerning the disease. The symptoms, 

 mode of occurrence, and general distribution were fully discussed in a 

 paper by Briggs, Jensen, and McLane (5). The disease is commonly 

 thought to result from some nutritional disturbance, but the cause has 

 not been definitely determined. 



