500 
J. ARTHUR HARRIS 
I now turn to the relative magnitude of the osmotic concentration 
of terrestrial and epiphytic plants. 
Since in a number of series of determinations we have found a 
differentiation in the sap properties of ligneous and herbaceous plants,^ 
I shall compare epiphytic Orchidaceae, Bromeliaceae, and Piperaceae 
primarily with terrestrial herbaceous plants. 
Unfortunately the several hundreds of determinations from the 
various coastal, pineland, hammock, and Everglade habitats of Sub- 
tropical Florida are as yet unclassified, and it will probably require 
some time before the results from this highly interesting region are 
discussed in detail. 
The averages for the various groups of epiphytes from Jamaica 
and from Subtropical Florida have been given in table i. 
The average freezing-point lowering of the saps ranges from 0.276° 
to 0.464'', less than two tenths of one degree. In terms of osmotic 
concentration the values lie between 3.3 and 5.6 atmospheres, a range 
of less than two and one third atmospheres. 
The only extensive series of averages for herbaceous terrestrial 
vegetation are those for the Arizona deserts made by Harris, Lawrence, 
and Gortner (191 6), and the first Long Island series, by Harris, 
Lawrence, and Gortner, as yet unpublished, and the Jamaican montane 
rain forest series which will be treated in greater detail below. 
For the Long Island habitats the preliminary average values are: 
Average Con- 
Habitat centration, P 
Beaches, coastal sand dunes, and marshes 13.62 
Dryer woods and open fields 10.04 
Permanently moist localities 9.27 
All habitats 10.41 
Note that the epiphytic forms show a sap concentration about 
one third to one half as great. 
For the Arizona desert (vernal) flora the averages for herbaceous 
plants are : 
^ For averages for divers growth forms from the Arizona deserts see Harris, 
Lawrence, and Gortner (1916). Averages for Long Island and Jamaican habitats 
are given by Harris and Lawrence (1917a). Some general comparisons are made by 
Harris (1917). 
