Oct* 2 , 1916 
Effect of Blackrot Fungus on the Apple 
35 
At the end of four hours the contents of the flasks were poured upon 
large filters, allowed to drain, and washed with distilled water until 
the total volume of the filtrate and washings equalled 500 c. c. A 
convenient portion of each filtrate was then titrated with iV/20 sodium 
hydroxid. As the tissues of the apple contain a natural indicator which 
develops a marked color upon neutralization, the method of titration 
employed was that described by Schley (23). The results given in 
Table V state in each case the number of cubic centimeters of N/20 
sodium hydroxid required to neutralize the acids in the clear filtrate 
from 40 gm. of fresh pulp. 
Table V. —Acidity in normal and diseased tissue of apple expressed in cubic centimeters 
of N120 sodium hydroxid required to neutralize the clear filtrate from 40 gm, of fresh 
pulp after four hours’ extraction with water 
Extraction and date. 
Normal. 
Half- 
decayed. 
Wholly 
decayed. 
Average for samples taken June 17: 
Cold water.. 
8-5 
4-3 
3- 4 
Hot water.;. 
ix. 7 
4 . 6 
4- 5 
Average for samples taken June 22: 
Cold water. 
9- 7 
6 . 0 
3-3 
Hot water. 
9- 7 
7 - 5 
4 . 0 
It is, of course, recognized that this method gives only comparative 
results, that a considerable portion of the acid content is not extracted 
by water, and that much higher figures would have been obtained had the 
titration been made directly upon the pulp suspended in water. It may 
be pointed out, however, that when titrations are made by the last- 
mentioned method, the diffusion of acids out of the tissues continues for 
many hours and at slower rates in diseased than in normal fruits, as 
experiments in this laboratory have shown. Hence, the employment of 
a method which combines rapidity of performance with the attainment* 
of consistent approximate results. As a check upon determinations made 
upon samples from the field, artificial inoculations and sterile checks 
containing 40 gm. each of pulp were prepared, sterilized, and inoculated 
for 33 days in all respects as previously described, and 150 c. c. of distilled 
water were then added to each flask. The flasks were heated on the 
water bath for 30 minutes, and duplicate portions were taken for titration. 
The neutralization of the acids of the sterile check required 66 c. c. of 
N/20 sodium hydroxid, for the inoculated pulp 3 c. c. were required. The 
acidity of the sterile check was therefore 22 times that of the culture. In 
natural infections, there is a reduction of acidity to about one-third that 
found in sound fruits. The growth of Sphaeropsis malovum upon the apple, 
whether under natural or artificial conditions, is therefore accompanied 
by a considerable reduction in the acidity of the tissues. Reed (18), in 
the course of his studies of the enzymic activities of Glomerella rufomacu- 
lans y observed that this fungus produced an alkaline reaction in originally 
