24 NOURISHMENT OF PLANTS. 



structure are freely at their service. For this reason, 

 then, an exact knowledge of the chennical elements 

 of plants, of the soil, of water, and of the air, must 

 be deemed absolutely indispensable, — the starting- 

 point, indeed, from which all subsequent inquiry 

 must proceed. 



The first question, then, which requires to be an- 

 swered in this connection, is of the following tenor : — 



1. Of what do Plants consist ? 



When the chemist wishes to investigate the compo- 

 sition of any body, he reduces it, in the first instance, 

 into its coarser components, and then again resolves 

 these into their finer elements. The former are 

 called the p7'oximate, and the latter the ultimate con- 

 stituents of bodies. If these last admit no further 

 separation into still simpler elements, they receive the 

 name of elementary substances^ or chemical elements. 



In this way numberless plants have been already 

 examined, and have been found to contain proxi- 

 mate constituents of very different character. In 

 many cases these can be readily distinguished from 

 each other by their appearance, taste, and other ex- 

 ternal characteristic marks. Grapes, carrots, and 

 many other fruits and roots, have a sweet taste ; 

 they contain sugar. The branches and leaves of 

 the grape-vine have a sour taste ; they contain an 

 acid salt. Those of the wormwood have a bitter 

 taste ; they contain a peculiar bitter principle. The 

 latter possess aleo a powerful odor, which proceeds 



