10 TRANSACTIONS. 



to ascertain what food is needed by plants, is to analyze their 

 whole substance, to see what ingredients they contain. For 

 the notion prevalent not long since, that vegetables have the 

 power to transmute one simple substance into another, is ut- 

 terly exploded ; and no scientific man now expects to find in 

 plants any ingredient that does not exist in the soil or the at- 

 mosphere. The uniform result of careful and repeated analy- 

 sis of plants is, that they are mainly and essentially composed 

 of four principles, viz : carbon, oxygen, hydrogen, and nitrogen. 

 These are combined together in various ways, and form the 

 almost entire mass of vegetables. But when plants are burnt, 

 they leave a solid residuum, or ash, which often contains eight 

 or nine other simple substances : viz : chlorine, iodine, sulphur, 

 phosphorus, potassium, sodium, calcium, magnesium, alumin- 

 um, silicon iroij, and manganese. These are the inorganic 

 ingredients ; and though essential to the composition of plants, 

 they do not always exist in the same proportions, even in the 

 same plant, as do the organic ingredients, that is, carbon, ox- 

 ygen, hydrogen, and nitrogen. Neither are any of these in- 

 gredients, organic or inorganic, found in a simple state, but are 

 united in various ways. 



The next grand inquiry is, Whence do plants derive their 

 twelve or thirteen ingredients? If we can answer this ques- 

 tion satisfactorily, we have gained an important step in ascer- 

 taining how the farmer can supply food to those plants which 

 he cultivates. As a general answer to the question, we may 

 say, that the soil and the atmosphere are the only sources 

 whence the vegetable world can derive its nourishment. And 

 analysis dhows that ordinarily all that is essential to its healthy 

 development is found there. Indeed, nearly or quite all of 

 these ingredients are usually found in the soil ; and the com- 

 mon impression is, that the greater part of the substance of 

 plants is derivpd from the soil; by means of the sap absorbed 

 by the roots, because it is necessary to add manure yearly to 

 render soils productive. But the opinion is now general 

 among chemists, and seems sustained by facts, that a large 

 proportion, — say about two thirds, — of the carbon contained 



