INFLUENCE OP MANURES. NITROGEN. 133 



that productiveness, which it is the aim of the cultivator to 

 obtain ; and it is in the choice of his materials, and the mode of 

 their application, that his skill and judgment are shown. The 

 science of Vegetable Physiology has been but too little connected 

 with the arts of the Farmer and Gardener ; and they have con- 

 sequently been working in the dark, frequently coming, after 

 tedious and unsuccessful trials, to conclusions which might have 

 been drawn immediately from scientific principles. The cer- 

 tainty with which the mode of operation of manures upon vege- 

 tation has been now ascertained, should lead to most important 

 improvements in practice, by which the productiveness of land 

 may be much increased. 



1 94. Although Carbonic acid and Water are the chief sources 

 of nourishment to Plants, there is one element of great import- 

 ance to their active growth, namely nitrogen, which is not 

 contained in either of these compounds. It might be thought 

 that, as so large a quantity of it exists in the atmosphere, no 

 difficulty could exist, in the introduction of as great an amount 

 of it as might be desirable, into the Vegetable system. But it 

 would seem that none of the elements, of which that system is 

 composed, can be introduced into it in a simple form. Thus we 

 have seen that the carbon is derived from carbonic acid, and the 

 oxygen and hydrogen from water : and it is found that plants 

 rather increase than diminish the quantity of nitrogen in the 

 atmosphere. Nitrogen is introduced in the form of ammonia, 

 the pungent gas which gives strength to hartshorn, smelling- 

 salts, c., and which is liberated by the decomposition of almost 

 all Animal substances, in which nitrogen very largely exists. A 

 great quantity of this gas is thus being constantly set free and 

 diffused through the atmosphere : but still it forms so small a 

 proportion of the whole, that it cannot be shown to exist in the 

 air, otherwise than in an indirect manner. Ammonia is very 

 readily absorbed by water ; and thus the rain arid dew, in de- 

 scending through the atmosphere, become impregnated with it, 

 although in very small amount. This ingredient can be proved 

 to exist in rain-water ; and thus its presence in the atmosphere 

 becomes certain. 



