58 CARNEGIE INSTITUTION OF WASHINGTON. 



common metals found in the soil and which are important in nutrition, 

 but it may not permit more complex substances to pass readily. 

 These features are represented in the new colloidal cell by the cylin- 

 drical clay cup used in the Livingston atmometer, which has a length 

 of about 12 cm. and an internal diameter of 2 cm., is closed at one end, 

 and has a capacity of from 35 to 40 c. c. The walls of the cup have a 

 thickness of about 2 mm., and when it is closed with a stopper with 

 suitable fixtures it may be used directly in osmotic tests of great in- 

 terest. Tests show that the solutions of the soil salts pass through 

 the clay walls almost as readily as water, while sugar and other organic 

 compounds are retarded, so that when such substances are used to fill 

 the cell a positive osmotic pressure may be set up. 



The plasmatic or living layer of the cell is represented in this cell 

 by a lining layer of a gel consisting of two parts of agar, one of gelatine, 

 and one-thousandth part of calcium or potassium oleate and an 

 equivalent amount of some lipin. A sufficient quantity of such a 

 mixture is poured into the cup while warm, so that when the cup is 

 closed by an osmometer head and the cup slowly rotated in the hand 

 the colloids set as a gel 3 mm. in diameter over the entire interior 

 surface. 



The osmometer head is fitted with a separatory funnel, by which 

 solutions representing the cell contents may be introduced, while a 

 second delivery or exit tube conducts out any excess which may accrue 

 from the positive action of the cell, and this is collected in a graduated 

 test-tube. When it is stated that the lining colloidal layer forms a 

 special layer where it comes in contact with the cell-wall, simulating 

 the plasmatic membrane of the living cell, the principal features of the 

 colloidal cell have been enumerated. 



Chief interest in the cell in the present connection centers in the 

 action by which it absorbs solutions from the soil or water in which 

 the plant may be growing. The most important experiments with the 

 new cell, therefore, were those in which it was given a sap or content 

 of varying character and placed in solutions of known composition 

 to test its action. The first illustration of the fact that the new cell 

 is not a simple osmometer consists in the difference in results when it is 

 filled with a sodium solution as contrasted with the effect of a potas- 

 sium solution of equimolecular concentration. The cell with the 

 potassium (chloride) sap and potassium soap in the plasma absorbs 

 about twice as much water as the sodium cell and ten times as much as 

 a calcium or magnesium cell with a sap of identical molecular concen- 

 tration. Furthermore, some of the effects of balanced solutions of 

 sodium and calcium are to be seen in the action of the new cell. 



Among the more interesting features of the action of this device are 

 the operations which parallel those of plasmolysis and of adaptive 

 adjustments of the living cell. Furthermore, as may be seen by the 



