THE OSMOTIC CONCENTRATION OF THE TISSUE FLUIDS 
OF JAMAICAN MONTANE RAIN-FOREST 
VEGETATION! 
J. Arthur Harris and John V. Lawrence 
I. Introductory Remarks 
Purpose of Investigation. — This paper is one of a series in which 
various problems involving the investigation of the osmotic pressure 
or osmotic concentration of the fluids of plant tissues are treated. 
Specifically it presents an extensive series of determinations of the 
freezing-point lowering of the extracted leaf sap of plants from the 
Blue Mountains of Jamaica, discusses the differences in these values 
in their relation to local differences in the environmental complex, and 
briefly compares the series as a whole with others now available. 
In another place (Harris, Lawrence and Gortner, 1916) we have 
put forward in detail the arguments for the carrying out of such 
studies as a regular part of systematic and thoroughgoing phyto- 
geographical investigation. It seems unnecessary, therefore, to repeat 
these arguments here. 
After completing a series of determinations of the osmotic con- 
centration of the tissue fluids of a number of species of plants from 
the southwestern deserts, in the vicinity of the Desert Laboratory 
during the winter and spring months of 1914, and comparing them 
(Harris, Lawrence and Gortner, 1 91 5) with a series made in the more 
mesophytic habitats in the neighborhood of the Station for Experi- 
mental Evolution on Long Island, the next most desirable step seemed 
to be the investigation of the sap properties of the plants of an ex- 
tremely hygrophytic region. 
Since such field studies could be most conveniently carried out 
during the winter months, at a time when we could be absent from 
1 Results of investigations carried on at Cinchona, by courtesy of the British 
Association for the Advancement of Science and the Jamaican local government, 
under the joint auspices of the department of botanical research and the department 
of experimental evolution of the Carnegie Institution of Washington, and with the 
collaboration of the New York Botanical Garden. 
268 
