THE CELL 57 



quantities of carbonic acid. Therefore, the two phases 

 of nutrition : the diffusion of nutrient substances and 

 their transformation into the very substance of the cell, 

 their assimilation, are closely related to each other. 

 One process is conditioned by the other : did assimila- 

 tion not take place there would be no more diffusion ; 

 did diffusion not take place there would be no matter 

 for assimilation. Moreover, since by means of such 

 assimilation the substance is transformed into a hardly 

 mobile or even totally immobile form, it does not diffuse 

 away again, but accumulates in the cell. 



When we examine the nutrition of the plant from 

 such a general, physical point of view, we get a concep- 

 tion of it quite different from the usual current ideas 

 upon the subject. It is not the plant, nor the cell, 

 which attracts or imbibes nutrient substances ; on the 

 contrary it is the nutrient substance itself which rushes 

 into the cell owing to its inherent mobility. A cell 

 is simply a microscopic centre, where the equilibrium of 

 the surrounding substances is constantly disturbed, a 

 kind of whirlpool, into which these very mobile sub- 

 stances rush in a continual stream, and within which 

 they lose their mobility, are transformed, and become 

 deposited. A vegetable cell is a trap which lets things 

 pass easily one way, but does not let them out again. 

 In this way we come to understand the fundamental 

 feature of vegetable life : increase of mass, accumulation 

 of matter. 



As we shall soon see, these general ideas as to the 

 nutrition of the cell will prove to be essential at almost 

 every step in our study of the phenomena of the nutrition 

 of the whole plant. The nutrition of the root by sub- 

 stances in the soil, the aerial nutrition of leaves by the 

 atmosphere, or the nutrition of one organ at the expense 

 of another adjacent to it — to arrive at the explanation 

 of any of these phenomena we shall have recourse to 

 the same fundamental causes : (i) diffusion, i.e. the 



