486 ORGANOLOGY. 



land always commences with the burning of the aboriginal wood, which 

 is occasionally done also in the Old World, especially in Russia. Amongst 

 the various burnings is also that of the Steppes, so frequent in the 

 Pampas and the prairies of North and South America. Exceeding all 

 these, are those incalculable quantities of carbonic acid which con- 

 tinually issue from volcanoes. When all these sources of supply are put 

 together, we can entertain no doubt that the carbonic acid annually pro- 

 duced upon the surface of the earth is abundantly sufficient to supply 

 all the demands of vegetation. 



The foregoing will serve to make clear the relation of plants to 

 carbon, and the great part which carbonic acid plays, and must play, in 

 the economy of nature. 



2. Nitrogen. The views of botanists upon the taking up of nitrogen 

 by plants are in a twofold manner opposed to those upon the appropri- 

 ation of carbon. It is eighty years since the discovery of oxygen and 

 its qualities by Priestley showed the immense importance of carbonic 

 acid to the vegetable world ; but there is. still at the present day a great 

 number of botanists, and theoretical agriculturists, and even some 

 chemists, who entertain the conviction that the organic matter of the 

 soil is received by plants in order to supply them with carbon. Again, 

 it has been recently ascertained that ammonia, and the salts of ammonia, 

 are the only essential sources of the nitrogenous contents of plants, al- 

 though there may yet be found persons ignorant enough to believe that 

 plants receive their nitrogen from the soil, and who overlook its change 

 in manures into ammonia and the salts of ammonia. The fact is, 

 it is simply impossible to oppose any thing to ammonia and its 

 salts as humus has been to carbonic acid. We are unacquainted with 

 any soluble organic substance containing nitrogen, which is present in 

 the earth in sufficient quantity to supply the necessities of plants, and 

 all experiments have led to the result that neither animals nor plants 

 are capable of assimilating nitrogen in its elementary form. There is 

 nothing left to the theorists on organic nutrition and vital powers but 

 to receive it in the form of ammonia. The simple question to be solved 

 here is, What are the sources of ammonia? and in the discussion of this 

 question it will be requisite to distinguish between cultivated plants and 

 those growing wild. 



It hardly needs to be observed, that plants growing wild are not sup- 

 plied with ammonia through manuring or other organic supplies ; nor 

 can they be, according to De Saussure, who was the first to point out 

 this fact, that the atmosphere is the source from whence plants derive their 

 volatile salts of ammonia, and which have been supplied from the soil. 

 A second source has been recently pointed out by Mulder, namely, the 

 formation of ammonia at the cost of the atmospheric nitrogen by the 

 putrefaction of non-azotised organic substances.* We can make no ac- 

 curate computation of the amount obtained in either way. We know 

 that the last result of the putrefaction and decomposition of substances 



* Mulder, moreover, regards as important, in which I agree with him, the gradual 

 formation of ammonia in the soil. I attach little value to the objection to De Saussure's 

 experiments, that in the decomposition of the non-azotised compounds, which for the 

 most part contain oxygen and hydrogen in the proportions to form water, there is 

 no free oxygen, which ought to be the case if the hydrogen combines with the nitrogen 

 to form ammonia. But it is highly probable that the sources of nourishment are 

 universally the same for all plants, and that this formation of ammonia, according to 

 Mulder, may occur on every primitive soil, and yet leave no organic matters. 



