168 HOW THIS INFLUENCE IS MANIFESTED. 



rectly conveyed to the plant by these nitrates, they also exercise sortie 

 other influence, by which they enable the hving vegetable to draw from 

 natural sources a much larger supply than they would otherwise be 

 capable of doing. What is this influence, and how is it explained? 



This I suppose to be that kind of influence to which writers on agri- 

 culture are in the habit of alluding, when they speak of certain substan- 

 ces stimulating plants, or acting as stimulants to their growth, though the 

 term itself conveys to the mind no distinct idea of the mode of opemtion 

 intended to be indicated — of the way in which the effect is produced. 



In the present case, this special action of ammonia and the nitrates, 

 and perhaps also of immediate applications of manure in general, ap- 

 pears to arise from their affording to the plant, in its early youth, a copi- 

 ous supply of nitrogenous food, by which it is enabled at once to shoot 

 out in a more healthy and vigorous manner. It thrusts forth roots in 

 greater numbers, and to greater distances, and is thus enabled to extract 

 nourishment from a greater extent and depth of soil than is ever reached 

 by the sickly plant — it expands larger and more numerous leaves, and 

 thus can extract from the air more of every thing it contains which is 

 fitted to supply the wants of the living vegetable; as the stout and 

 healthy savage can hunt and fish to support many lives, while the feeble 

 or sickly can scarcely secure sustenance for himself alone. Feed a wild 

 animal well the first few months of its life, and you may set it loose to 

 prey for itself; starve it in its infancy, and its growth and strength will 

 be stunted, and it may lead a wretched and hungry life. * 



Even in soils, then, and situations, which are capable of yielding to 

 the plant every thing it may retjuire for its ordinary growth, it is an im- 

 portant object of the art of husbandry to discover what substances are 

 especially necessary or grateful to particular crops, and to apply these 

 directly^ and in abundance, to the new-born plant, — in order that it may 

 acquire sufficient strength to be able to avail itself in the greatest degree 

 of the stores of food which lie within its reach. 



Concluding observations regarding the organic constituents of plants. 



We have now considered the most important of those questions con- 

 nected with the organic elements of plants, which are directly interesting 

 lo the practical agriculturist. We have seen — 



1°. That all vegetable productions consist of two parts — one the or- 

 ganic part, which is capable of being burned away in the air — the other, 

 the inorganic part, which remains behind in the form of asli. 



2°. That this organic part consists of carbon, hydrogen, oxygen, and 

 nitrogen only. 



3°. That plants derive the greater part of their carbon from carbonic 

 acid, of their hydrogen and oxygen from water, and of their nitrogen 

 from ammonia and nitric acid. 



4°. That by far the largest portion of those substances which form 

 the principal mass of plants, such as staxch and woody fibre, consists of 

 carbon united to oxygen and hydrogen in the proportions in which they 



more than half the quantity, which in consequence of the presence and action of the nitrate 

 the wheat was enabled to obtain and appropriate above the quantity appropriated by the 

 wheat in the un-nitrated part of the field. 



It requires no further proof, therefore, to show that the nitrate of soda and the nitrates must 

 act in some other way in reference to vegetation, than by simply supplying aportion of nitrogen. 



