5OO 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, 5 

 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 (1916), 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 Lawrence, and Gortner, as yet unpublished, and the Jamaican montane 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- 2 7 



All habitats 



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 : 



6 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 (19170). Some general comparisons are made by 

 Harris (1917). 



