1 88 Journal of Agricultural Research voi.xx.No.j 



phosphorus, on the other. Usually the nitrogen content of mottled 

 leaves is also abnormally high. The composition of mottled orange 

 leaves resembles that of immature leaves, although the percentages of 

 ash and nitrogen in the former are materially greater than in the latter. 



It has been shown that the absolute amounts of potassium and phos- 

 phorus contained in mottled orange leaves are fully as great as ordi- 

 narily occur in normal leaves that are two or three times as large, while 

 the calcium content is not more than one-third that occurring in average 

 normal leaves. 



The sap of normal orange leaves becomes increasingly concentrated and 

 acidic as growth proceeds. When mature it is especially rich in calcium 

 and contains fully twice as much of this element as of potassium. 



The abnormalities of mottled leaves noted above also occur in the sap 

 and among the water-soluble constituents. The sap of mottled leaves 

 contains subnormal amounts of calcium and fully twice as high concentra- 

 tions of potassium and phosphorus as mature normal leaves. The 

 hydrogen-ion concentration of mottled leaves is not materially different 

 from that of normal leaves, but the sap is less nearly saturated with base. 

 In other words, abnormally large amounts of unionized acids occur in 

 mottled-leaf sap. 



Limited study of portions of citrus trees other than the leaves in- 

 dicates that the composition of the leaf spurs of severely mottled trees 

 varies from the normal in much the same way as the leaves. The compo- 

 sition of the older wood, however, is more nearly normal. On the other 

 hand, both the large roots and small rootlets of severely mottled trees 

 appear to contain considerably less potassium and phosphorus than nor- 

 mal roots, while the calcium content is approximately normal. 



Should more extended study confirm these latter observations, it 

 would seem that the excessive proportions of potassium and phosphorus 

 occurring in mottled leaves may have been drawn, in part at least, from 

 the supply normally stored in the roots. 



The results of these investigations suggest that mottled citrus trees 

 are deficient in calcium, but the cause of the subnormal content of 

 calcium can not be definitely stated. 



While we recognize that growing plants have the power, through 

 selective absorption, of regulating their composition to a marked degree, 

 and that a given variation in the composition of a plant does not neces- 

 sarily reflect a corresponding deficiency in the nutrient medium, the above 

 data suggest that the abnormalities in the composition of different parts 

 of mottled citrus trees may be due, in part at least, to the inability of the 

 tree to satisfy its normal calcium requirements at critical periods. 



It is well known that manure and other forms of decaying organic 

 matter exert an ameliorating effect on mottle-leaf. It is interesting in 

 this connection that the concentration of soluble calcium in the soil 



