OSMOTIC CONCENTRATION OF TISSUE FLUIDS 273 
The freezing-point lowering of the filtered sap was determined by 
means of ether or carbon bisulphide vaporized by a dried air current 
in a vacuum jacketed bulb. 
The results are expressed in terms of freezing-point lowering, 
A, corrected for undercooling, and in atmospheres pressure P from a 
published table (Harris and Gortner, 1914). 
Classificatio7i of Habitats. — In these studies it has been our policy 
to adopt in so far as possible the classification of plant habitats drawn 
up by specialists in ecology or phytogeography. Such a course makes 
for simplicity and lack of confusion in the literature, lends added 
value to such habitat studies as have already been made by correlating 
with them new kinds of observations, and finally precludes any possi- 
bility of bias in the classification of determinations in a way to make 
them agree with any preconceived theory. 
For the Blue Mountain region it has been possible to follow the 
classification presented in the splendid work of our colleague Forrest 
Shreve (1914) whose extended experience in the montane region of 
Jamaica and whose analyses of the previous scattered literature and 
meteorological data have made it unnecessary for us to go back of his 
large publication on the region. 
For descriptive details presented in a most readable manner and 
a wealth of carefully selected illustrations the reader must turn to 
Shreve's book. Here only the most salient and essential points will 
be set forth. 
The fundamental division is that into the two main slopes of the 
mountain chain. These are designated as windward and leeward 
rather than northern and southern to emphasize the predominant 
influence of the moisture-laden trade winds in determining the char- 
acteristics of the vegetation. The subdivision of the two main slopes 
is made on the basis of topography, into ravines, slopes and ridges. 
In carrying out our work we have found it desirable to emphasize 
certain of these regions at the expense of others. Such descriptive 
details as are essential will be given under the discussions of the 
individual habitats. 
We have not found it practicable to consider individually all of 
the five types of habitats recognized by Shreve. 
Because of the morphologically xerophilous character of its scrub 
vegetation we desired to investigate rather fully the sap properties 
of the '"ruinate" of the once cleared southern slopes. This seemed 
