302 BOTANICAL GAZETTE é [APRIL 
attempted again by another method. Citrus mottle leaf offers 
another example of an interesting discrepancy between the titre 
and the H-ion concentration (36 
TANNIN.—The conspicuous fact brought out in figs. 3 and 6 is 
the great increase in tannin in the b samples in the first stage of 
growth. This indicates that in these half-grown fruits the tannin 
increases rapidly after the fruit is picked from the tree, but that if 
the fruit is infected by the fungus the tannin does not increase. 
Cook and his colleagues (3, 16, 17) report an enzyme that forms 
tannin rapidly either when the fruit is picked or when it is wounded. 
The former fact is corroborated in the present work, but not the 
latter. In fact, infection by the fungus not only does not cause 
an increase in the tannin content, but in varieties C and SCF in 
fig. 3 there is a decrease over the fresh samples. ‘Two facts should 
be kept in mind in this regard: first, that the great increase in 
tannin after picking from the tree occurs only in the half-grown 
stage of growth; and second, that the decrease in tannin in the 
rotted samples is noticeable only in the two later stages of growth, 
since unfortunately in the first stage the fresh sample was analyzed 
only in the case of AXW 30. In fig. 6 it can be seen that in the 
fresh samples of the second stage the resistant varieties have a 
lower content of tannin than the susceptible, and that in the sound 
samples of the first stage the facts are reversed. It is difficult to 
perceive any facts that can be correlated with resistance characters. 
VALLEAU (46) came to the same conclusion. 
OxaLic acip.—Figs. 4 and 6 give the analyses for oxalic acid 
in the juice and in the residues from the juice. In all cases there 
was a small amount of oxalic acid present in the juice of the fresh 
fruit, as judged by the reduction of permanganate. It does not 
average over 0.02 per cent of the juice. In most cases there is 
more oxalic acid in the c than in the a or b samples, indicating that 
during the rotting a production of the acid takes place. This is 
in accordance with the findings of CooLry (19), who reported that 
oxalic’ acid was produced by Sclerotinia. The amount of oxalic 
acid produced in the rotted plums, however, seems insufficient to 
exert any very marked solvent power on the tissues. Although the 
data for oxalic acid in the residues are very incomplete, they indicate 
