THE OSMOTIC CONCENTRATION OF THE SAP OF 

 THE LEAVES OF MANGROVE TREES. 1 



J. ARTHUR HARRIS AND JOHN V. LAWRENCE, 

 STATION FOR EXPERIMENTAL EVOLUTION, COLD SPRING HARBOR, N. Y. 



I. PROBLEM AND METHODS. 



The morasses of insular and continental coasts in the tropical 

 zone of both eastern and western hemispheres are largely occupied 

 by a vegetation consisting almost exclusively of a number of 

 species of trees or shrubs collectively designated as mangroves. 



These species, belonging to different genera and families, are 

 characterized by striking morphological and biological features, 

 for example, the prop or stilt roots of Rhizophora, the negatively 

 geotropic roots, breathing roots or pneumatophores of Avicennia, 

 and the remarkable vivipary and seedling dispersal of Rhizo- 

 phora. 



These various peculiarities have attracted the universal in- 

 terest of biological travelers in the tropics. 



The physiology of a group of organisms characterized by such 

 morphological features and growing under environmental con- 

 ditions so specialized presents a most interesting group of prob- 

 lems. When, however, one turns to the literature he is impressed 

 by the fact that conclusions concerning the physiology of these 

 plants are chiefly deductions from all too superficial field ob- 

 servations and from macroscopic and microscopic anatomical 

 investigations. Physiological constants, properly so called, are 

 practically wanting. Thus the recording of any quantitative 

 data on the physiology of this ecologically fascinating group of 

 plants is especially desirable. In the present paper we shall not 

 summarize or comment upon the available literature, but shall 

 limit ourselves to the presentation of the results of certain meas- 

 urements carried out on the southern shore of the island of Jamaica 



1 Cooperative studies carried out by the Department of Experimental Evolution 

 and the Department of Botanical Research of the Carnegie Institution of Washing- 

 ton. 



2O2 



