DETERMINATION OF ACIDITY IN PLANT 
TISSUES 
By HERBERT M. RICHARDS 
Barnard College, Columbia University 
For many physiological purposes the determination of the 
concentration and amount of acids in plant juices is a matter of 
importance. Acid formation or acid splitting may affect the 
output of carbon dioxide and thereby alter the gas interchange 
relations. It is necessary to be informed as to the amount of 
its rise and decline to evaluate properly the energy-releasing 
processes connected with respiration. It is known also that the 
degree of acidity in an imbibed fluid has an important influence 
on the hydratative capacity of colloidal systems and therefore 
must affect the colloidal mélange of protoplasm. Besides this the 
concentration of acids in the vacuole has an important bearing 
upon the osmotic coefficient of its contents. Without attempting 
then to enumerate all the ways in which a knowledge of the acid 
content of plant juices may be of physiological importance, it is 
evident that the determination of this factor is necessary. 
In this very brief communication it is not intended to give even 
a partial survey of the problem, or to touch upon the variety of 
methods which have been developed for the isolation of definite 
acids. For technical purposes many ways have been devised by 
which the acids in various fruits and other plant parts can be 
determined and extracted in a manner that is satisfactory for the 
results required. That these methods may not be applicable to 
some physiological problems is not a criticism of their technical 
value; but, at the same time, it is questionable in some instances 
whether the acids extracted really represent either in quantity 
or condition the acids originally present in the living cell. 
In the first place, the manner of obtaining the plant juices 
may be considered. The common method is by pressure. As 
far as concentration is concerned, the juice squeezed out may 
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