CONCENTRATION OF TISSUE FLUIDS OF EPIPHYTES 503 



If the comparison be made with the ligneous terrestrial vegetation, 

 the differences are 6.07 for the Leeward and 5.45 for the Windward 

 habitats. 



In relative terms, the osmotic concentrations of the sap of the 

 epiphytic Orchidaceae is only 37.3 to 46.5 percent as high as that of 

 the terrestrial herbs of the same habitat, the constants for the Bromeli- 

 aceae range from 42.3 to 49.6 percent of the comparable values for 

 terrestrial herbs, while the determinations based on Peperomia range 

 from 52.9 to 60. i percent of those for the non-epiphytic herbs of the 

 same habitats. Columnea shows a concentration of 56.9 percent of 

 that of herbaceous plants in the Windward habitats and 62.7 percent 

 of that of herbaceous plants in the Leeward habitats. If compared 

 with ligneous terrestrial vegetation it shows a concentration of 44.0 

 percent in the Windward and of 44.0 percent in the Leeward habits. 



Summarizing the results of this comparison : the osmotic concentra 

 tion of the fluids of the epiphytic Orchidaceae, Bromeliaceae, Piper- 

 aceae, and Gesneraceae of the montane rain forest of Jamaica is roughly 

 speaking only 37.3 to 62.7 percent as high as that of the terrestrial 

 plants of the same region. 



The averages for herbaceous forms include, as already explained, a 

 few determinations based on species which may occur on the ground or 

 as epiphytes. They also include those based on a few ferns and fern 

 allies. The removal of these constants might change slightly the actual 

 values of the difference in the table. Since the forms which have been 

 classified as terrestrial but may occur as epiphytes are characterized by 

 lower osmotic concentration than the vegetation as a whole, the re 

 moval of these species from the list of herbaceous plants would make 

 the differences demonstrated between terrestrial and epiphytic vege 

 tation even larger. The exclusion of the few determinations for 

 terrestrial ferns and fern allies could be justified only on the assump 

 tion that they are sensibly differentiated in their sap properties from 

 flowering plants. There is, at present, no basis for such an assumption. 



The low concentration of the sap of epiphytic Phanerogams may 

 perhaps be most clearly brought out by comparing it with that of the 

 ligneous species upon which they may occur. Table 5 gives the 

 differences and relative concentrations for the Jamaican materials. 



Epiphytic Orchidaceae show from 28 to 36 percent, the epiphytic 

 Bromeliaceae from 32 to 38 percent, the epiphytic Piperaceae from 

 39 to 45 percent, and the epiphytic Gesneraceae about 44 percent 



