Feb. 2,1924 
Tissue Fluids in Cotton 
275 
Dixon and Atkins (12) and ourselves (16, 17). Freezing-point lowering, 
A; specific electrical conductivity, k; and hydrogen-ion concentration, 
expressed as P n , were then determined on the centrifuged sap, extracted 
from the tissue by pressure. 
In the first series of determinations (see p. 283) the physical measure¬ 
ments were made as soon as possible after the extraction of the leaf 
fluids. In the second series the expressed sap was allowed to stand over¬ 
night in the ice box. 
Freezing point lowering was measured by means of a mercury ther¬ 
mometer graduated to hundredths of degrees. Electrical conductivity 
was determined at 30° in Freas conductivity cells standardized against 
N/10 KC 1 , considered as having a conductivity of 0.01412 reciprocal ohm 
at 30°. The Washburn half-meter bridge with extension coils, giving 
10 M. of wire, and a Leeds and Northrup resistance box was used. 
Hydrogen-ion concentration was measured by means of the Wendt 
modification of the Hildebrand assemblage. In this method a calomel 
cell charged with normal KC 1 , a small Weston Millivoltmeter and a slid¬ 
ing resistance of 500 ohms with current capacity of one ampere were 
used. Hildebrand, Sharp, Hoagland, and others (10) have recognized 
the limitations of precision of this method. The accuracy of the physical 
measurements is, however, sufficient for the comparisons which are 
emphasized in this paper. 
In discussing these acidities we must not forget that the determina¬ 
tions were made on sap extracted by pressure from killed tissues. Haas 
(18) has stated that a considerable change in reaction may take place 
in the cell as it dies (from P H 3 to P H 7), but he evidently refers to the 
changes taking place in the natural ageing and death of the cells, rather 
than to errors introduced by the killing of the cell and the extraction of 
the cell sap. His own determinations were made by means of extracts 
obtained by rapidly macerating petals in a mortar with the solvent. 
McClendon and Sharp (44) noted an increase in the acidity of freshly 
expressed carrot juice on exposure to the air for a short time. They also 
give some data on P H of fluids extracted from boiled and unboiled tissues. 
Finally, Atkins (1) has noted a similar increase in the acidity of expressed 
sap on exposure to the air, and suggests a coordination of this result 
with those obtained by Bunzell (8) on acidity and oxidase activity. It 
is also possible, as noted by Hoagland and Davis (35), that extracellular 
substances in the tissues may influence the concentration or reaction of 
the cell sap after the crushing of the tissues. 
Whatever may be the results of further investigations on the relative 
values of the hydrogen-ion concentration of extracted sap as compared 
with that of the sap occurring in the tissues, the facts remain (a) that 
the only method by which the problem of hydrogen-ion concentration 
may be investigated in a series like the present is upon extracted sap, 
(b) that the technique used introduces no artificial differences between 
the biological series considered, and (c) that, as will be shown below, the 
results for the various series considered here show a high degree of con¬ 
sistency, thus indicating that there is no highly variable disturbing 
factor in the technique. 
The results in the accompanying tables are expressed in terms of 
freezing-point depression, A, corrected for the amount of ice separating on 
under-cooling. Those who prefer to consider the results in terms of 
atmospheres may transmute the values of freezing-point lowering given 
