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THE FARMERS' REGISTER. 



able; but there is a great gulf, as it appears to 

 us, belwixt the obvious conclusion from this— ihat 

 humic acid, namely, and iis earthy salts, can con- 

 tribute but little to the general nourishment of 

 plants, and that which he atiecls to draw I'rom it 

 —that humic acid in no other way can directly 

 contribute to the nourishment ol plants, and that 

 the only use of the entire vegetable matter in the 

 soil is, by its decay, to yield carbonic acid to the 

 roots. The compounds of humic acid, with 

 potash, soda, and ammonia, are very soluble in 

 water, and it has yet to be proved that they may 

 not, especially in manured land, be present in the 

 soil, and be thence taken up by the roots, while it 

 is certain, also, that other soluble organic sub- 

 stances do exist about the roots, which, therefore, 

 may enter into the circulation of the plant and aid 

 its growth. In philosophical questions, a distinct 

 line should be drawn between clearly established 

 facts, or conclusions legitimately Ibrmed from 

 them, and the mere opinions even of the rpost 

 eminent men. On the whole, we are inclined 

 to hold a middle way, and with our author to 

 consider it to be satisfactorily established, that, 

 while a plant sucks in by its leaves and roots 

 much carbon, in the form of carbonic acid, it 

 derives a variable portion of its immediate sus- 

 tenance (of its carbon) from the soluble organic 

 substances that are within reach of its roots. 



This fact is never doubted by the practical hus- 

 bandman. It forms the basis of many of his 

 daily and most important operations, while the 

 results of these operations are further proofs of 

 the fact. 



We pass on to another important question con- 

 nected with the food of plants, in regard to which 

 the views of our author difi'er to some extent Irom 

 another of those opinions propounded in so broad 

 and general a manner in the recent work of 

 Liebig. We allude to the source of the nitrogen 

 of plants. There are two compounds from which, 

 according to our author, there is reason to suppose 

 that plants, in the general vegetation of the globe, 

 derive the greatest proportion of their nitrogen. 

 These compounds are ammonia, which consists 

 of' nitrogen and hydrogen ; and nitric acid, which 

 is composed of nitrogen and oxygen only. The 

 beneficial action of ammonia upon vegetation 

 has been long recognized in practice, experiment- 

 ed upon by philosophical agriculturists, and 

 brought prominently forward by writers upon 

 theoretical and practical agriculture. It is given 

 off in the gaseous state during the decay of the 

 bodies and excretions of animals; and therefore 

 wherever such are added, intentionally or other- 

 wise, to the soil, the ammonia they yield rnust 

 be considered as the source of a portion of the 

 nitrogen which the plants that grow there are 

 found to contain. In one of those numerous ex- 

 perimental papers With which Boussingault has 

 enriched theoretical agriculture, he adverted to the 

 opinion which had been long entertained by some 

 that ammoniacal vapours probably float in the at- 

 mosphere in minute quantity, and suggested that 

 those vapors might probably be a natural source 

 of a portion of the nitrogen which is known to 

 be present in plants. This opinion in regard to 

 the presence of ammonia in the atmosphere, was 

 founded upon the known fact that ammonia does 

 escape into the air during the decay of animal 

 substances, and that experimenters, Brandes, 



among others, as early as 1825, had found am- 

 moniacal salts in rain water. Liebig, who also 

 found a sensible quantity of ammonia in rain 

 water, has recently been led to propound the opi- 

 nion that all the nitrogen contained in plants 

 enters them in the form of ammonia, and that the 

 minute portion which floats in the atmosphere 

 is the source from which ihey derive this am- 

 monia when it is not present already in sufficient 

 quantity in the soil. On reading his chapter on 

 this subject, we could not help granting— what 

 we were indeed prepared to concede, and in which 

 all recent practical and theoretical writers concur 

 —Ihat ammonia is ol great value in promoting 

 vegetation, and that it is one source ol the nitro- 

 gen of plants; but when we found ourselves in 

 the midst of a paragraph, which assumed it to be 

 proved that ammonia is the only source from 

 which their nitrogen is derived, we fancied that 

 we must have inadvertently missed an important 

 step in the argument, and we turned back again 

 and carefully retraced our steps in seach ol the 

 missing link in the chain of reasoning— but in 

 vain. °Il is proved that ammonia is very useful 

 to vegetation, and ought never to be wasted in 

 good husbandry ; but it is thence assumed by 

 Liebig to be the only source of nitrogen to living 

 vegetables. We are the more particular in in- 

 sisting upon this, because the wriier, borne away 

 by his own belief, expresses himself as if he had 

 really deduced his opinion from legitimate pre- 

 mises, and because we have seen many notices of 

 his book, in which, what is merely an opinion ol 

 the writer, is really supposed to be proved. But 

 we should be sorry to think that such an opinion 

 was capable of prool, lor we are quite sure that 

 it does not truly represent the ordinary procedure 

 of nature. 



The author of the work now before us ap- 

 pears to be so far of the same opinion with our- 

 selves, that he mentions another important source 

 of nitrogen to the general vegetation of the globe, 

 as he expresses it, t)esides the ammonia— namely, 

 nitric acid, a compound consisting, as we have 

 already said, of nitrogen and oxygen only. The 

 arguments upon which he rests this opinion are 

 slated in his eighth lecture, and are perfectly 

 satisfactory. To us one authoriiy, not quoted by 

 Mr. Johnston, is conclusive. In a work ol the 

 celebrated Berzelius ol Stockholm, now belore us, 

 and which was written in 1829, long belore the 

 opinions now in question were agitated, it is 

 staled, " that every flash of lighming thai passes 

 through the air must produce a not inconsiderable 

 quaniTty of nitric acid ;" and we have seen enough 

 of the incessant lightnings of South America, 

 and of the thunders that piecede the monsoons 

 in India, to satisfy us that the quantity of nitric 

 acid produced in the air must be really enormoiis. 

 When, in addition to this, we recollect that the 

 nitrates of potash and soda have been observed 

 in all climates to promoie vegetation when ar- 

 tificially applied to plants, we are inclined to think 

 that in the following summary of his views,' 

 which for the sake of brevity we extract Irora his 

 Elements, the agency of niiric acid is rather under 

 than over stated by our author. . 



"IS uric acid is also naturally formed, and iQ 

 some countries probably in large quantities, by 

 the passage of electricity through the atmosphere. 

 The air, as has been already staled, contains 



