Nov.. 1. 19-0 Composition of Normal and Mottled Citrus Leaves 187 



analyses in that they indicate that the composition changes materially 

 as growth proceeds and that the composition of mottled leaves differs 

 from that of normal leaves. 



It is interesting to note that the total water content of mottled and 

 normal mature leaves is roughly correlated with the concentration of 

 the sap, but this correlation does not hold when immature leaves are 

 compared with mature leaves. 



GENERAL DISCUSSION 



It has been shown that the composition of orange leaves changes 

 rapidly as growth takes place. The relationships between the several 

 constituents drawn from the soil undergo important alterations. The 

 percentages of potassium and phosphorus, when expressed on the basis 

 of either the ash or the dry matter, decline rapidly during the early part 

 of the growth cycle and continue to decline, although at reduced rates, 

 during the latter part of the growth period. The percentages of nitro- 

 gen in" the dry matter also decrease as growth proceeds. The percent- 

 age of calcium, on the other hand, increases rapidly at first, and later 

 more slowly. The concentration of iron is greatest in very young leaves, 

 but later its concentration decreases slowly, while no very pronounced 

 changes take place in the percentages of the other constituents. The 

 concentration of the different constituents probably remains practically 

 constant throughout the period of normal maturity. 



As the leaves approach senility just preceding the time of normal 

 dropping, notable amounts of potassium and nitrogen are translocated 

 back into the stem or other portions of the tree. A part of the phos- 

 phorus also appears to leave the leaf sometime preceding the period of 

 normal maturity. In contrast to certain cereals, the absolute content 

 of magnesium does not decrease as maturity approaches. 



It has been shown that a given orange leaf normally contains the 

 maximum amounts of potassium, phosphorus, and nitrogen by the time 

 it is approximately 6 weeks of age. It is interesting that the leaf also 

 reaches its maximum size about the same time. On the other hand, the 

 absolute content of calcium continues to increase until full maturity is 

 reached. 



Mature orange leaves are extremely rich in certain nutrients. The con- 

 tent of carbonated ash ranges from 14 to 18 per cent of the dry matter, and 

 the nitrogen content is usually above 2 per cent. The most pronounced 

 characteristic of the orange leaf, however, is found in its highly calcareous 

 nature. When the leaf is mature, the dry matter contains from 5 to 6 

 per cent of calcium. 



Lemon and grapefruit leaves are similar in composition to orange leaves. 



The composition of mottled citrus leaves is widely different from that 

 of normal leaves. The difference lies mainly in the smaller calcium 

 content, on the one hand, and the greater content of potassium and 



