80 ON THE PLANT-CELL. 



CHAPTEE II. 



ON THE LIFE OF THE PLANT-CELL. 



SECTION I. 



FUNCTIONS OF THE INDIVIDUAL CELL. 



30. ALL the chemical and physical powers of the earth naturally 

 act upon the plant-cell. Inasmuch as these striking phenomena are 

 called forth, and especially as they exhibit, in and through the cell 

 itself, an especial form of action, I call all such action the life (vita) 

 of the cell. Most of the physical powers of nature are too little 

 known for us to be able to comprehend the peculiarities which they 

 exhibit under especial relations. We can only say generally that 

 the various chemical processes which take place in the cell must 

 be accompanied by changes of temperature, electricity, absolute 

 and specific gravity, &c., without being able to count or measure 

 the same. There are, therefore, only a few relations which permit 

 of a more accurate estimation, as the absorption of foreign agents 

 (endosmosis), the decomposition and recomposition of the same (as- 

 similation and secretion), the getting rid of superfluous matter 

 (exhalation and excretion), the working up of the assimilated 

 matter (organisation), the movements of the contents of the cell 

 (circulation), the movement of the whole cell (locomotion), the 

 formation of new cells within the old ones (propagation), and the 

 cessation of all these processes (death). 



I. On the Absorption of Foreign Agents. 



31. The cell-membrane (in its young state) is perfectly closed, 

 but permeable to all fluids. It thus takes up all perfect solutions 

 through its walls into its cavity. In consequence of the chemical 

 change going on in its interior, the cell constantly contains a fluid 

 thicker than water, or dilute solutions of saline substances, and 

 mostly one which, like a solution of sugar or gum, has so great an 

 affinity for water, that they draw water into the cavity with a cer- 

 tain degree of force, and, on the other hand, a small quantity of the 

 concentrated fluid passes out of the cell. The passing in of the 

 fluid into the cell has been called by Dutrochet endosmose, and its 

 passing out exosmose. 



The property which cellulose possesses of allowing fluids to pass 

 through it has already been mentioned. It is an entirely superfluous 



