48 MASSACHUSETTS AGRICULTURE. 



to transmute one simple substance into another, is utterly 

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

 any ingredient tliat does not exist in the soil or the atmosphere. 

 The uniform result of careful and repeated analysis of plants 

 is, that they are mainly and essentially composed of four princi- 

 ples, A'iz. : carbon, oxygen, hydrogen and nitrogen. These are 

 combined together in varioiis 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, aluminum, silicon, 

 iron and manganese. These are the inorganic ingredients ; 

 and though essential to the composition of plants, they do not 

 always exist in the same proportio\is, even in the same plant, as 

 do the organic ingredients, — that is, carbon, oxygen, hydrogen 

 and nitrogen. Neither are any of these ingredients, organic or 

 inorganic, found in a simple state, but arc united in various 

 ways. 



The next grand inquiry is, Whence do plants derive their 

 twelve or thirteen ingredients ? If we can answer this question 

 satisfactorily, we have gained an important step in ascertaining 

 how the farmer can supply food to those plants which he culti- 

 vates. 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 shows 

 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 common impression is, 

 that the greater part of the substance of plants is derived 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 sus- 

 tained by facts, that a large proportion, — say about two-thirds, — 

 of the carbon contained in plants, is absorbed directly from the 

 atmosphere by their leaves. And yet only 2 sVo"^^^ P^^'^ °^ ^^^® 

 atmosphere is carbonic acid, which is diffused through the whole 

 air, and less than one-third of this gas is carbon. How then 

 can a tree or forest, for instance, obtain enough of this gas to 

 form so large a part of its substance ? since the quantity imme- 

 diately around it, and even the fresh portions brought by the 



