Nov. i, 1920 Composition of Normal and Mottled Citrus Leaves 171 



Among the other necessary nutrients, the percentages of iron, magne- 

 sium, and sulphate decreased with age, although to a lesser degree than 

 potassium and phosphate. The ash of the youngest leaves contained 

 approximately twice as much iron as that of the mature leaves, and 

 differences almost as great occurred in the percentages of magnesium 

 and sulphate. 



As was anticipated, the changes that take place in Valencia orange 

 leaves are quite similar to those of navel leaves. 



The percentages of phosphorus and sulphur refer to the total amounts 

 as determined by the magnesium-nitrate and sodium-peroxid fusion 

 methods, respectively, and are somewhat higher than the corresponding 

 data calculated from the ash analyses. As is well known, organic 

 materials usually lose a portion of their phosphorus and sulphur in the 

 ashing process. 



It will be noted that the content of water decreased considerably as 

 growth took place. At 1 week of age the navel leaves contained 72.31 

 per cent water, at 6 weeks 70.81 per cent, at maturity 60.98 per cent, 

 and the very old leaves still contained 60.73 P er cent. The content of 

 total ash, on the other hand, increased markedly with age, rising from 

 6.54 per cent of the dry matter at the age of 1 week to the very high 

 content of 21.39 P er cent in the old leaves. 



The nitrogen decreased from 3.01 per cent at the age of 1 week to 2.39 

 per cent at maturity, and finally to 1.31 per cent in the old stage. The 

 percentage of phosphorus decreased still more rapidly during the actively 

 growing period, but later the phosphorus content remained approxi- 

 mately constant. The percentage of potassium also decreased rapidly 

 during the early period of growth but remained almost constant after 

 the second period until the period of senility approached, when a still 

 further decrease took place. 



The percentage of iron in the dry matter was found to be reasonably 

 constant at all stages of growth. However, in considering the iron con- 

 tent of these and all other samples reported herein, it is important to 

 bear in mind that the analytical error involved in the determination of 

 small amounts of this element is likely to be relatively great. For this 

 reason small variations in the results are probably not significant. 

 The percentages of sulphur and magnesium each increased somewhat 

 as growth took place. 



The constituent of the dry matter of orange leaves that undergoes the 

 greatest percentage change as a result of growth is calcium. At 1 week 

 of age, the navel leaves contained 1.36 per cent calcium, at 6 weeks 

 2.62 per cent, at maturity 5.63 per cent, and the very old leaves contained 

 7.36 per cent. 



Of the supposedly unessential constituents, the greatest concentration 

 of sodium was found in the young leaves; but the amount was always 

 small, while the data for silica and chlorin show no consistent variation. 



