ASSIMILATION OF MATTER BY PLANTS. 35 



and the leaves, are the only means by which 

 plants can derive their supply of food. 



The spongelets of the roots, taking up the 

 liquid matter which is found in the soil, and 

 the leaves absorbing the various gases, which 

 serve as a pabulum for the plant, from the 

 air. 



Thus plants, in contradistinction to the ani- 

 mal tribes which exist on a mixture of solid and 

 liquid food, exist entirely on liquids, as nothing 

 can be absorbed by the root which is not in a 

 fluid state, and the gases taken up by the leaves 

 are equally fluids in a much more subtle state 

 of division. 



From the most careful and recent chemical 

 analysis of the matter, forming the structure 

 of plants, it appears that all the various sub- 

 stances which enter into the composition of the 

 vegetable tribe are reducible into the four fol- 

 lowing simple gases, viz. 



Carbon, 



Nitrogen, 



Hydrogen, 



Oxygen; 

 and that these gases, combined in different pro- 

 portions, and mixed with such earthy matters 

 as potash, soda, lime, phosphorus, and magne- 

 sia, are the simple substances from which all 

 vegetable products are elaborated. 



To give, therefore, such an account of the 

 means employed for this purpose, as shall 

 carry conviction on the subject, it is proposed 

 to consider each body separately, — defining 



