Apr. lo, 1916 



Citrus Canker 



87 



to be correlated with the acidity of the cell sap. Because of these several 

 facts, an effort has been made to determine whether the difference in 

 susceptibility between Satsuma oranges and grapefruit can be accounted 

 for on the basis of difference in acidity. Leaves collected from plants 

 growing in the greenhouse were used in these tests. The leaves were 

 finely macerated by trituration; distilled water was then added to make 

 a volume equaling 200 times the weight of the finely ground leaves; 

 phenolphthalein was added as an indicator; and the acids present in the 

 sample were titrated with N/io sodium hydroxid. This method is open 

 to criticism where absolutely accurate determinations are sought, but 

 is regarded as satisfactory in indicating relative differences. Consider- 

 able variations in acidity of the same species were noted, dependent 

 largely upon the cessation of photosynthetic activity at night. Greater 

 acidity, as would be expected, occurred in samples collected early in the 

 morning. Representative results of these tests, however, are shown in 

 Table I. 



Table l.—Acidiiy of oranges and grapefruit 



The leaves of Satsuma oranges are consistently higher in acid content 

 than those of grapefruit, since the former require 1.0184 c. c. of N/io 

 sodium hydroxid to neutralize i gm. of wet weight of leaf tissue, young 

 Satsuma leaves, 0.9735 c. c, old grapefruit leaves, 0.8787 c. c, and 

 young grapefruit leaves, 0.8634 c. c. When the acidity of the cell sap is 

 computed on the basis of the total moisture content of the leaves, it is 

 found to be 1.691 per cent for old Satsuma leaves, 1.465 per cent in those 

 of young Satsumas, 1.490 per cent in those of old grapefruit, and 1.080 



