ABSORPTION, DIFFUSION, OSMOSE. 21 



drawn out of the cell-sap, but the substances in solution in the cell-sap do not 

 readily move out. As the bulk of the cell-sap diminishes the pressure from 

 the outside pushes the protoplasmic membrane away from the wall. Now 

 when we remove the salt solution and bathe the thread with water again, the 

 cell-sap, being a more highly concentrated solution than water, diffuses 

 with more difficulty and the diffusion current is inward, while the protoplasmic 

 membrane moves out against the cell wall, and turgidity again results. Also 

 in the experiments with salt and sugar solutions on the leaves of geranium, on 

 the leaves and stems of the seedlings, on the tissues and cells of the beet and 

 carrot, and on the root hairs of the seedlings, the same processes take place. 



These experiments not only teach us that in the protoplasmic membrane, the 

 cell wall, and the cell-sap of plants do we have structures which are capable of 

 performing these physical processes, but they also show that these processes are 

 of the utmost importance to the plant ; not only in giving the plant the power 

 to take up solutions of nutriment from the soil, but they serve also other pur- 

 poses, as we shall see later. 



