The Plantlet. 47 



its dissolved constituents, is commonly called sap, ex- 

 cept in fruits, when it is usually called juice. 



63. How Food Materials are Distributed through 

 the plant. If we drop a bit of aniline blue into a glass 

 of clear water, it will not retain its form and size, but 

 infinitely small particles will become detached and move 

 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 distrib- 

 uted 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 sub- 

 stances 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 the 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 dif- 

 ferent parts. The water absorbed by the root-hairs 

 (100) is not chemically pure, but holds in solution small 

 quantities of various soluble matters contained by the 



