ON THE DIFFERENTIATION OF THE LEAF TISSUE 

 FLUIDS OF LIGNEOUS AND HERBACEOUS 

 PLANTS WITH RESPECT TO OSMOTIC 

 CONCENTRATION AND ELEC- 

 TRICAL CONDUCTIVITY.* 



By J. ARTHUR HARRIS, ROSS AIKEN GORTNER, and JOHN V. LAWRENCE. 



{Frorp, the Department of Experimental Evolution and the Department of Botanical 

 Research, the Carnegie Institution of Washington, Washington.) 



(Received for publication, October 30, 1920.) 



The existence of a differentiation of ligneous and herbaceous plants 

 with respect to the magnitude of the osmotic concentration of the 

 tissue fluids was first demonstrated in a strictly quantitative manner 

 by work on the sap of the plants of the spring flora of the Arizona 

 deserts^ in the neighborhood of the Desert Botanical Laboratory, and 

 on the terrestrial vegetation of the Jamaican montane rain forest.^ 

 These studies, in two geographically widely separated and climati- 

 cally dissimilar regions, and an extensive series of unpublished obser- 

 vations demonstrate that the leaf tissue fluids of ligneous plants are 

 characterized by an osmotic concentration materially higher than 

 that of herbaceous forms. 



The magnitude of the specific electrical conductivity, K, of the 

 fluids must now be considered in comparison with osmotic concen- 

 tration as measured by the freezing point lowering, A, for a series of 

 plant species on which both of these constants were determined. 



The determinations here considered were made on the north shore 

 of Long Island during the spring and summer of 1914 and 1915. Leaf 



* Studies carried out by the cooperation of the Department of Experimental 

 Evolution and the Department of Botanical Research of the Carnegie Institution 

 of Washington, The results will be published in full in the Journal of Physical 

 Chemistry. 



^ Harris, J, A., Lawrence, J, V., and Gortner, R, A,, Phys. Researches, 1916,, 

 ii, 1. 



2 Harris, J, A., and Lawrence, J, V., Am. J. Bot., 1917, iv, 268. 



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