ABSORPTION, DIFFUSION, OSMOSE. 21 



the thread with water again, the cell-sap, being a solution of certain sub- 

 stances, diffuses with more difficulty than the water, 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 solu- 

 tions on the leaves of geranium, on the leaves and stems of the seedlings, on 

 the tissues and cells of the beet and carrot, and pn the root hairs of the seed- 

 lings, 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. 



