ON THE OSMOTIC PRESSURE OF THE TISSUE FLUIDS 
OF JAMAICAN LORANTHACEAE PARASITIC 
ON VARIOUS HOSTSi 
J. Arthur Harris and John V. Lawrence 
1. Introductory Remarks 
This paper, which is one of a series on various physiological, 
ecological, phytogeographic, and evolutionary problems involving a 
knowledge of the physico-chemical properties of vegetable saps, has 
for its object the presentation of a series of observational data on one 
phase of the water-relations of tropical Loranthaceae — the osmotic 
pressure of their tissue fluids in comparison with that of their hosts. 
Since our method of attack upon the physiology of the Loran- 
thaceae is so far as we are aware quite novel, it has seemed most 
expedient to focus attention sharply and practically exclusively upon 
the actual results of our studies, reserving a detailed discussion of the 
literature until other work now planned and under way has been 
completed. 
Whatever the answer to the mooted question of the nature of the 
solutes obtained by the parasite from its host — whether solely mineral 
or both mineral and plastic — the nature and the magnitude of the 
forces by which the solution containing these substances is drawn from 
the tissues of the host is a subject of fundamental importance. 
Furthermore, few botanists would, we beheve, be inclined to 
question the validity of the proposition that among these forces one 
of the fundamental variables is the osmotic pressure of the fluids 
contained in the tissues of the two organisms.^ 
^ Results of investigations carried on at Cinchona, by courtesy of the British 
Association for the Advancement of Science and the Jamaican Local Government, 
under the joint auspices of the Department of Botanical Research and the Depart- 
ment of Experimental Evolution of the Carnegie Institution of Washington, and with 
the collaboration of the New York Botanical Garden. 
2 As far as we are aware the only botanists who have actually published this 
view are MacDougal and Cannon (1910) and MacDougal (1911a, 191 1&), who con- 
sidered a higher osmotic pressure in the sap of the engrafted organism to be one of 
the essentials of experimentally induced parasitism. 
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