86 THE NUTRITIVE FUNCTIONS. 



fluid or gaseous condition. This is absolutely necessary, in 

 order to render it susceptible of being conveyed through 

 the vessels and of permeating the walls of the cells, which 

 we have seen to be the ultimate structure of the organism 

 of both plants and animals. With reference to plants, no 

 such reduction of their food to a gaseous or fluid state is 

 necessary, because they live in the midst of their food, and 

 in perpetual contact with it. 



If we plant a seed in the ground, it grows from the very 

 commencement of vital motion, in two opposite directions, 

 upwards into the atmosphere and downwards into the 

 earth : the two grand sources from whence it obtains the 

 materials which contribute to its future growth. We may 

 consider a plant then as a vegetable axis or stem, more or 

 less ramified at its two extremities. That portion of the 

 stem growing into the atmosphere puts forth from its 

 branches, during the season of vegetable activity, certain 

 flat, dilated organs, which we call leaves, the surface of 

 which is porous and by means of which food is absorbed 

 from the atmosphere. That portion of the stem which 

 ramifies in the ground, on the other hand, becomes covered, 

 about the same time, with numberless delicate white fibres, 

 which are the true roots of the plant. These correspond 

 to the leaves on the branches, performing the same func- 

 tion, that of absorption, and like the leaves decay and 

 become detached from the plant in autumn. On the 

 return of spring, the underground and atmospheric rami- 

 fications of the plant are again re-clothed, the former with 

 fibres and the latter with leaves. 



It is a mistake to suppose that all the underground por- 

 tion of a plant is the root. The white delicate fibres put 

 forth in early spring, at the time that the leaves .grow on 

 the branches in the atmosphere', are the true roots ; they 



