398 Necessity and Advantage of Scientific Enquiry 



it cannot be doubted that much remains to be done, to make the 

 science of horticulture complete. It is not a recent discovery, 

 that the results of the decomposition of animal and vegetable 

 matters impart fertility to the earth ; nor that the same oper- 

 ations and applications of manure, being made and performed 

 on different lands, would produce different effects ; and it must 

 always have been desirable to ascertain the cause of this dif- 

 ference. But as the earth, water, and air, as well as animal 

 and vegetable matters, are all combined to produce the differ- 

 ent effects, the cause could not have been discovered by any 

 other means, than by ascertaining what elementary substances 

 enter into the composition of vegetables, and also what elements 

 are contained in the other compound substances; and then, 

 by comparison, we may discover what part of these elements 

 could be furnished by each, or either, of the compound sub- 

 stances, and thus be enabled to judge how far one could make 

 good the deficiencies of the other ; and as this could only be 

 done by a decomposition and analysis of all the different sub- 

 stances concerned in vegetation, it could not have been effected 

 by our ancestors. 



These important operations, however, have been performed 

 by the chemists of the present day; and the following re- 

 sults appear to be generally admitted to be just : — The earth 

 is a compound of various metallic oxides, but as it is not 

 found to exist in, or to affect, vegetables, in any other state 

 than as argil or clay, silex or flint, and limestone and mag- 

 nesia, it has not been thought necessary to push the ana- 

 lysis further. Water is formed by a combination of oxygen 

 and hydrogen ; air is a compound of nitrogen and oxygen. 

 All vegetable substances are proved to be formed by a combin- 

 ation of hydrogen, oxygen, carbon, and earth ; and animal sub- 

 stances are a compound of oxygen, nitrogen, hydrogen, carbon, 

 and earth. By a comparison of the elements forming these 

 compound substances, it appears that the earth and water 

 contain, and are capable of supplying, all that is required for 

 the composition of vegetables, except carbon ; and that by the 

 decomposition of animal and vegetable substances, in and on 

 the earth, carbon is furnished. It must be concluded then, 

 that carbon is the nutritive principle, or the element whose 

 absence or presence determines the fertility of the soil ; and 

 which cannot be supplied by earth and water only. 



The next object to be considered must be, what carbon is, and 

 how, and in what state, it is to be obtained and made available 

 to plants ; and herein we find the chemists at fault : for all we 

 learn from them is, that carbon takes its name from coal, of 

 which it appears to be the basis, but from its affinity for other 



