300 BOTANICAL GAZETTE [October 



f 



about this stage of growth of the plant. They are thus quite 

 comparable with the concentrations of certain of the solutions 

 used in the sand and water culture experiments. In every instance 

 the osmotic pressure of the plant sap is much higher than that 

 of the nutrient medium. 



All of the samples of plant sap have a very high specific con- 

 ductivity, and very decided variations are exhibited by the 

 different water cultures. The concentration of the nutrient 

 solution has unquestionably had a pronounced effect on the elec- 

 trolyte content of the cell sap. A somewhat greater resistance is 

 found in the root sap than in that from the tops. It is to be 

 noted, however, that the variations in conductivity due to the 

 nutrient solution are generally as great for the tops as for the 

 roots, but in either case only a general relationship is apparent. 

 The conductivities of the plant saps from the various soils were 

 very similar in magnitude to those of the plants grown in water 

 culture solutions of 0.5 to 0.9 atmospheres osmotic pressure. 

 The conductivities of the sand culture plants were somewhat 

 greater, but these plants were two weeks younger. In each case 

 the expressed cell sap has a much higher concentration of electro- 

 lytes than the surrounding media, the relationship being 50 : i in 

 the case of the most dilute solution. Thus the nutrient media, 

 the root sap, and sap from the tops show three very dissimilar 

 levels of electrolyte concentration. That the simple laws of 

 diffusion are not sufficient to explain the equilibria involved in 

 the plant absorption and metabolism is well recognized, and the 

 data now presented strikingly illustrate this point of view, with 

 reference to the ion content of the plant and its nutrient solution. 



H ion concentration of sap 



Haas (3) and Truog (7) have shown that the sap of plants 

 quite generally has an H ion concentration distinctly on the 

 acid side. Determinations of H ion concentration were made on 

 the samples of sap obtained as previously described. Table I 

 shows a comparison of the acidity of the sap from plants grown 

 in water cultures of very different concentration and reactions, 

 as well as in sand and soil media. 



