126 J. A. Harris, R. A. Gartner and J. V. Lawrence 



dissimilar regions (and by extensive unpublished series) that 

 the leaf tissue fluids of ligneous plants are characterized by an 

 osmotic concentration materially higher than that of her 

 baceous forms. 



The magnitude of the specific electrical conductivity of 

 the fluids must next be considered in comparison with osmotic 

 concentration as measured by the freezing point lowering. 



II. The Osmotic Concentration and Specific Electrical 



Conductivity of the Leaf Tissue Fluids of 



Herbaceous and Ligneous Plants of a 



Mesophytic Flora 



The determinations here considered were made on the 

 north shore of Long Island during 1914 and 1915. Leaf 

 tissue was collected in large test tubes. After freezing in an 

 ice-salt mixture 1 to render the tissue permeable, as has been 

 shown to be necessary by Dixon and Atkins 2 and by our 

 selves. 3 The sap was extracted as completely as possible by 

 pressure, cleared by centrifuging and the freezing point lower 

 ing, A, was determined in the usual manner. Correction 

 was made for the ice separating on undercooling by the for 

 mula 



A = 0.0125 u A , 



where u is the undercooling and A the observed freezing point 

 lowering in degrees. 



The specific electrical conductivity, K, of the sap was 

 measured at 30 C in a Freas conductivity cell, standardized 

 against N/io KC1, which has a specific conductivity 0.01412 

 reciprocal ohms at 30, by means of the ordinary meter bridge 

 wire and resistance box of the physiological laboratory. 



All determinations were made with as great care as possi 

 ble, but there are many possible sources of error, and some 

 selection of the constants to be used in the present paper seems 



1 R. A. Gortner and J. Arthur Harris: Plant World, 17, 49-53 (19*4)- 



2 H. H. Dixon and W. R. G. Atkins: Proc. Roy. Soc. Dublin, 13, 422- 

 433 (1913)- Also in Notes Bot. Sch. Trin. Coll., Dublin, 2, 154-172 (1913). 



3 R. A. Gortner, J. V. Lawrence and J. Arthur Harris: Biochem. Bull., 5, 

 139-142, pi. i (1916). 



