292 BOTANICAL GAZETTE [APRIL 
tissues of the plums, after the latter had been sterilized with 
mercuric chloride. The plums were left to rot as long a time as 
was practicable, which was usually from five to seven days after 
all the tissue had turned brown to the stone. The same degree of 
rotting was not obtained in all cases, since this cannot readily be 
judged. 
Methods 
PREPARATION FOR ANALYSIS.—In preparing the samples for 
analysis the stones were removed, the pulps frozen in an ice and 
salt mixture for three hours, ground in a food grinder, and pressed 
in a hydraulic press. All manipulations were maintained as uni- 
form as possible throughout the series. The expressed juice was 
then used for all the subsequent analyses. Harvey (26) has shown 
that, in order to obtain the true P,, of a juice, the latter should be 
expressed without freezing, since the freezing precipitates certain 
proteins and thus changes the H-ion concentration. This fact had 
to be ignored in the present instance, however, since the determina- 
tion of the other solutes must be made on juice from frozen tissue, 
and since the amount of material available was not large enough 
to admit of two samples of juice being taken in each case. It 
might be of interest to record the results of a single test of the effect 
of freezing. The material was some seedling plums about one-third 
grown. 
Frozen Unfrozen 
Percentage of pulp obtained as juice.......... 70 
Bo ose bc ee a i 1.67 1.48 
SPECIFIC GRAVITY.—The specific gravity was obtained by means 
of a Westphal balance, after the juice had stood at least an hour. 
TITRATABLE ACIDITY.—Because of the high pigmentation of the 
juices soon after expression, titration by means of an indicator was 
impossible; hence the electrical conductivity method was employed. 
The peak of the curve could be read with an error of about = 0. 3 CC. 
0.1 N NaOH 
HYDROGEN-ION CONCENTRATION.—The electrometric method 
was used for determining the P, of the juices. Considerable 
trouble was experienced with the poisoning of the electrode by the 
