NOURISHMENT OF PLANTS. 43 



Thus far, then, on the constituents of plants, and 

 the means of nourishment by which they are provid- 

 ed. The table here exhibited may be regarded as 

 a retrospective view of the essential elements and 

 nutritive materials of plants, and may perhaps ren- 

 der still clearer w^hat has been communicated in re- 

 lation to these topics. 



How Nature proceeds in order to develop from 

 the three nutrients, carbonic acid, water, and am- 

 monia, with the aid of a few mineral substances, the 

 innumerable proximate constituents of vegetables, is 

 a subject upon which we still know nothing. That 

 which is called into existence by the creative power 

 inherent in living plants, we cannot imitate by art, 

 although we know with certainty that it avails itself 

 of chemical forces for the performance of its works. 

 On the other hand, we can imitate several of those 

 transformations of one vegetable substance into 

 another, (for instance, the conversion of starch into 

 gum, of gum into sugar, of sugar into oxalic acid,) 

 which are produced by the vital activity of plants 

 during the period of their growth. In this respect, 

 indeed, art can accomplish more than Nature ; for it 

 can effect combinations such as alcohol, ether, pyro- 

 ligneous acid, chloroform, gun-cotton, and a thou- 

 sand other compounds, which we never find ready 

 made in living plants. 



No doubt, however, now prevails in relation to the 

 fact, that the elementary substances contained in the 

 nutritive materials above mentioned are sufficient to 



