The Plantld. 47 



about to all parts of the water in which it dissolves. 

 This movement will not stop until the bit has entirely 

 disappeared, and until every part of the water contains 

 exactly as much of the aniline blue as every other part. 

 This equal distribution of the soluble material takes 

 place in response to the law of diffusion, that tends to 

 cause any soluble substance to become equally distributed 

 throughout the liquid in which it is placed. The liquid 

 in the meantime may remain stationary. The process 

 would be the same if we were to put in a very small 

 quantity of each of several soluble substances at the same 

 time. The movements of one of these substances would 

 not interfere much with those of the others. 



If we could remove some of the dissolved aniline blue 

 from the water in one part of the glass, it would follow 

 that the dissolved aniline blue would move from the 

 other parts toward this point, and if this removal were 

 continuous, slow currents would move in this direction 

 from all other parts of the glass. 



We may now understand how the materials from which 

 the plant is built up are distributed to its different parts. 

 The water absorbed by the root-hairs (101) is not chem- 

 ically pure, but holds in solution small quantities of vari- 

 ous soluble matters contained by the soil, some of which 

 are used by the plant in growth. As these useful mat- 

 ters are removed from the water of the cells, to be 

 formed into food (59), the supply is replenished from 

 the soil, not through any power of selection possessed by 

 the ptant, but in accordance with the law of diffusion. 

 In like manner, the food formed by the chlorophyll (59) 

 finds its way to the growing parts. Soluble matters not 



