54 THE LIFE OF THE PLANT 



be reached in our illustration ? Apparently not ; as 

 soon as our iron salt penetrates into our cell, it enters 

 into combination with the tannin, forming what for the 

 sake of brevity we shall call ink. Therefore the cell 

 will contain ink, but no more iron salt, and if it does not 

 contain any iron salt a fresh supply of the salt will 

 enter from the vessel outside ; this in turn will become 

 ink, and so on. If the bladder contains a sufficient 

 quantity of tannin, the equilibrium will never be reached, 

 and the iron salt will diffuse into our cell in a continual 

 stream. Thus we have only to take the collodion 

 bladder containing the solution of tannin, and put it 

 down into the vessel containing the solution of iron 

 salt, to withdraw from this solution the whole of its 

 salt and transfer it into the bladder. Let us put 

 aside this apparatus for a few hours or days, and we 

 shall find that there is no more iron salt in the outer 

 vessel : our artificial cell will consume it, will absorb it 

 completely. 



Apparently we are approaching the simple physical 

 explanation of the way nutrient substances enter into 

 the vegetable cell. We have seen that a gaseous or 

 soluble substance penetrates into a cell spontaneously, 

 and goes on penetrating into it until it finds itself 

 present equally on both sides of the cell-wall. We have 

 noticed further that this equilibrium will never be 

 established if the substance which penetrates into the 

 cell is transformed there and enters into a new combina- 

 tion. In that case it will rush into the cell in a per- 

 petual and continuous stream, and become precipitated 

 therein. We perceive here one of the reasons why the 

 mass of a plant increases, i.e. why matter becomes 

 accumulated in it ; but to complete our explanation we 

 require one more Hnk in the chain. The process of the 

 accumulation of matter in a cell will become quite clear 

 only in so far as we admit that substances enter freely 

 from outside into the cell, and that those into which 



