DETERMINATION OF MOISTURE CONTENT OF 
EXPRESSED PLANT TISSUE FLUIDS’ 
Ross AIKEN GORTNER AND WALTER F, HOFFMAN 
The fact that the physico-chemical properties of plant tissue 
fluids reflect in many instances the ecological environment of the 
plant, and that the ability of a plant to exist under widely different 
environmental conditions appears to depend largely upon its ability 
to adjust the physico-chemical properties of its tissue fluids to the 
new environment has only recently been recognized. Harris (3) 
has pointed out that any thorough ecological study should include 
physico-chemical studies of the plant saps. GORTNER and HARRIS 
(1) have indicated some of the precautions which must be taken 
in order to secure an accurate measure of the osmotic pressure of 
expressed plant saps by the cryoscopic method, and in subsequent 
papers Harris and his co-workers (4, 5, 8-14) have investigated the 
physico-chemical properties of plant saps in a variety of habitats. 
The physico-chemical determinations which have been used have 
necessarily been limited to those which are adapted to field labora- 
tory facilities, and which do not require excessive amounts of either 
time, apparatus, or plant materials. The determinations have 
therefore been confined exclusively to the measurement of osmotic 
pressure by the cryoscopic method, the electrical conductivity by 
the conventional wheatstone bridge, and more recently hydrogen 
ion concentration (unpublished data). 
Throughout all this work it has been recognized that a knowl- 
edge of the moisture content of the expressed plant saps would be 
most desirable. For example, a knowledge of the total solids com- 
bined with the depression of the freezing point would permit the 
calculation of the “average molecular weight” of the dissolved 
solutes. An increase in “average molecular weight” in a different 
environment might logically be interpreted as indicating a response 
‘Contribution from the Division of Agricultural Biochemistry, University of 
Minnesota; published with the approval of the Director as Paper no. 322, Journal 
Series, Minnesota Agricultural Experiment Station. 
Botanical Gazette, vol. 74] [308 
