Equilibrium in the Intake of Salts hy Plant Cells. 449 



been for the physiology of nutrition of plants to become more and more a 

 biochemical study of organs, or a biochemical study of the cell, rather than 

 a study of the mode of living of the plant, yet it is perfectly obvious that it is 

 neither possible nor desirable always to use the whole plant as the experi- 

 mental object, and so long as the conditions of experiment are borne in 

 mind, experiments on isolated cells or tissues should yield results of value 

 which supplement those obtained by experiments with the whole living 

 plant. 



In this paper we deal with the absorption by plant tissue of salts presented 

 singly to the tissue, and especially with the position of the equilibrium 

 attained in this intake of salt, and the influence of the concentration of salt 

 both on the rate of absorption and on the position of the equilibrium. 

 Although a number of different salts were employed, the influence of the 

 nature of the salt on the rate of its absorption is only touched upon briefly 

 here ; this question forms the subject of another paper. 



Method. 



The essentials of the method used are as follows. A number of discs o 

 tissue of uniform dimensions are immersed in the experimental liquid and 

 the change in electrical conductivity of the latter measured. In this way an 

 approximate value is obtained of the change in ionic concentration of the 

 external solution. The experimental tissues employed were those of potato 

 and carrot, but, for reasons which will be explained later, carrot was 

 chiefly used. 



In order to prepare the discs, cylinders of tissue were obtained by means of 

 a cork -borer of the necessary diameter, and the cylinders cut into discs of 

 the required thickness by means of a hand microtome. They were then 

 washed in distilled water thoroughly, or in tap-water followed by distilled 

 water, and finally, -lightly dried between blotting-paper before being used for 

 an experiment. 



In each experiment 100 c.c. of solution were employed, in which were 

 immersed 40 discs of a diameter of 1*8 cm. and a thickness of 1 mm. The 

 experiments were all performed in triplicate, which gives sufficient accuracy, 

 as the regularity of the results obtained indicates. In all series in which the 

 results were compared, the whole of the discs used in the series were mixed 

 together and the sets of 40 discs for each individual sample were then taken 

 from the general stock. It has been shown previously (13) that by this 

 means the error arising from inherent differences in different samples of 

 tissue may be considerably reduced. Comparisons are only made between 



2 N 2 



