ON THE OSMOTIC CONCENTRATION OF THE TISSUE 
FLUIDS OF PHANEROGAMIC EPIPHYTES^ 
J. Arthur Harris 
INTRODUCTORY REMARKS 
The purpose of this paper, which is one of a series deahng with the 
problem of the physico-chemical properties of vegetable saps in relation 
to environmental factors and to geographical distribution, is to present 
the results of three series of determinations of the osmotic concentration 
of the tissue fluids of phanerogamic epiphytes, and to compare them 
briefly and in a preliminary way with available data for the osmotic 
concentrations found in the sap of terrestrial vegetation. 
Notwithstanding the enthusiastic interest aroused in the mind of 
the botanical traveler by the remarkable range of form and the obvious 
physiological peculiarities of the Orchidaceae, Bromeliaceae, and other 
epiphytic forms so characteristic of tropical vegetation, our knowledge, 
in quantitative terms, of the physiology of these organisms is exceed- 
ingly meager. 
Since I hope on another occasion to discuss epiphytism in greater 
detail, I shall not in this place review the general literature. 
MATERIALS AND METHODS 
In this paper I have meant to include only those species which may 
unquestionably be considered typical epiphytes. It was for this reason 
that a few determinations made on plants which may be either terres- 
trial or epiphytic were included by Mr. Lawrence and myself in our 
paper on the Jamaican montane rain forest vegetation (1917a). In 
some instances it is extremely difficult to determine just which species 
shall be regarded as epiphytes. Our data are given in detail, and any 
botanist who chooses may arrange them differently. 
The methods employed in the present study are those sufficiently 
described in our earlier discussion of the parasitic and the terrestrial 
vegetation of the Blue Mountains (Harris and Lawrence, 1916, 1917a). 
1 This study was made possible by the Department of Botanical Research and 
the Department of Experimental Evolution of the Carnegie Institution of Wash- 
ington. 
490 
