292 
J. ARTHUR HARRIS AND JOHN V. LAWRENCE 
xerophytic region about the Desert Laboratory at Tucson and the 
more mesophytic vegetation in the neighborhood of the Station for 
Experimental Evolution on Long Island. 
Since carrying out the Jamaican determinations we have been able 
to make very substantial beginnings on the investigation of several 
other habitats, for example the forests of the upper Santa Catalina 
mountains and the various transition stations to the desert floor in 
southern Arizona, the Everglades, the Pinelands, and the hammocks 
of sub-tropical Florida, rich in West Indian species. A detailed 
comparison of the montane rain forest with other regions may profit- 
ably be reserved until the completion of these studies. In the mean- 
time it is worth while to indicate to phytogeographers and ecologists 
the relative position of the Blue Mountain habitats in the series 
concerning which published data are available. 
Consider first the values for the rain-forest plants as compared 
with those obtained in more mesophytic regions. Two such series are 
available, that of Ohlweiler ('12) based on trees and shrubs growing 
at the Missouri Botanical Garden, and that of Harris, Lawrence and 
Gortner ('15) for Long Island habitats. 
Ohlweiler's St. Louis series suffers from two disadvantages as 
regarded from the standpoint of this paper. First, it is based upon 
a series of species brought together from various natural habitats 
and cultivated in a botanical garden. All the species were, however, 
capable of growth in the open under the conditions prevailing at St. 
Louis. Second, sap was extracted without antecedent freezing of the 
leaf tissue. ^ As a result the freezing-point lowerings recorded are 
probably too low. 
Ohlweiler's series comprises trees and shrubs only. Comparing 
with the general average for ligneous plants from the Blue Mountains 
the results are : 
The trees and shrubs growing in the Botanical Garden at St. Louis 
show, therefore, a concentration of their leaf sap of from 2 to 5 atmos- 
pheres higher than do those of the various Blue Mountain habitats, 
and over 3 atmospheres more than the average for the Blue Mountain 
region as a whole. 
Means 
St. Louis series 
Blue Mountain series. 
14.96 
11.44 
