[Reprinted from the AMERICAN JOURNAL OF BOTANY, 5: 490-506, November, 1918.] 



ON THE OSMOTIC CONCENTRATION OF THE TISSUE 

 FLUIDS OF PHANEROGAMIC EPIPHYTES 1 



J. ARTHUR HARRIS 

 INTRODUCTORY REMARKS 



The purpose of this paper, which is one of a series dealing 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 (191 70). 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, 19170). 



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. 



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