PRESIDENT HITCHCOCK'S ADDRESS. 161 



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

 gen, hydrogen, and nitrogen. Neither are any of these ingredi- 

 ents, organic or inorganic, found in a simple state, but are united 

 in various ways. Thus the oxygen and hydrogen exist in the 

 form of water ; the carbon forms that portion of a plant which 

 may be converted into charcoal ; and the nitrogen constitutes 

 one part of albumen, gluten, and other vegetable products. 



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 develop- 

 ment is found there. Indeed, nearly or quite all of these ingre- 

 dients are usually found in the soil ; and the common impres- 

 sion is, that the greater part of the substance of plants is derived 

 from the soil, by means of the sap absorbed by the roots, be- 

 cause it is necessary to add manure yearly to render soils pro- 

 ductive. 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 in plants, is absorbed di- 

 rectly from the atmosphere by their leaves. And yet only 2-gWh 

 part of the 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 

 quan4ity immediately around it, and even the fresh portions 

 brought by the wind, must soon be exhausted. But here a 

 very wonderful law of nature completely provides for the diffi- 

 culty. If several sorts of gas or air be brought together, even 

 though some be much heavier than others, they will soon be- 

 come equally mixed throughout ; and if any one of them be 

 removed from a particular spot, what remains of the same gas 

 in other portions of the mixture will instantly expand, till it 

 has filled the whole space, just as it would do if that were the 

 only gas present. So that, if all the carbonic acid around a par- 

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