526 ' KEroRT— 1880. 



Lastly, in a letter received from Boussingault some j'ears ago, referring to the 

 sources whence tlie nitrogen of vegetation is derived, lie says : — 



' From the atmosphere, because it furnishes ammonia in the form of carbonate, 

 nitrates, or nitrites, and various kinds of dust. Theodore de Saussure was the first 

 to demonstrate the presence of ammonia in the air, and consequently in meteoric 

 waters. Liehig exaggerated the influence of this ammonia on vegetation, since he 

 went so far as to deny the utility of the nitrogen which forms a part of farm-yard 

 manure. This influence is nevertheless real, and comprised witliin limits which 

 have quite recently been indicated in the remarkable investigations of M. Schlosing. 



' From the soil, which, besides furnishing the crops with mineral alkaline sub- 

 stances, provides them -w-itli nitrogen, by ammonia, and by nitrates, which are 

 formed in the soil at the expense of the nitrogenous matters contained in diluvium, 

 which is the basis of vegetable earth ; compounds in which nitrogen exists in stable 

 combination, only becoming fertilising by the effect of time. If we take into 

 account their immensity, the deposits of the last geological periods must be con- 

 sidered as an inexliaustible reserve of fertilising agents. Forests, prairies, and 

 some vineyards have really no other manures than what are furnished by the 

 atmosphere and by the soU. Since the Ijasis of all cultivated land contains 

 materials capable of giving rise to nitrogenous combinations, and to mineral sub- 

 stances, assimilable by ])lants, it is not necessary to suppose that in a system of 

 cultivation the excess of nitrogen found in the crops is derived from the free nitro- 

 gen of the atmosphere. As for the absorption of the gaseous nitrogen of the air by 

 . vegetable earth, I am not acquainted ynt\i a single irreproachable observation that 

 establishes it ; not only does the earth not absorb gaseous nitrogen, but it gives it 

 off", as you have observed in conjunction ^^^th Mr. Lawes, as Reiset has shown in 

 the case of dung, as M. Schlosing and I have proved in our researches on nitri- 

 fication. 



' If there is one fact perfectly demonstrated in physiology, it is this of the non- 

 assimilation of free nitrogen by plants ; and I may add by plants of an inferior 

 order, such as mycoderms and mushrooms (Translation).' 



If, then, our soils are subject to a continual loss of nitrogen by drainage, pro- 

 bably in many cases more than they receive of combined nitrogen from the atmo- 

 sphere — if the nitrogen of our crops is derived mainly from the soil, and not from 

 the atmosphere — and if, when due return is not made from without, we are draw- 

 ing upon what may be termed the store of nitrogen of the soil itself — is there 

 not, in the case of manj' soils at any rate, as much danger of the exhaustion of 

 their available nitrogen as there has been supposed to be of the exhaustion of their 

 available mineral constituents ? 



I had hoped to say something more about soils, to advance our knowledge re- 

 specting Avhich an immense amount of investigation has been devoted of late years, 

 but in regard to which we have yet very much more to learn. I must, however, 

 now turn to other matters. 



I have thus far directed attention to some pomts of importance in connection 

 with the sources of the constituents of our crops, and I must now briefly refer to 

 some in connection with the composition, and to some relating to the uses, of the 

 crops themselves. 



As to composition, I must confine mj-self to indicating something of what is 

 known of the condition of the nitrogen in our various crops ; though I had intended 

 to say something respecting the carbo-hydrates, and especially respecting the 

 varioiis members of the cellulose group. 



As to the nitrogen — in our first experiments on the feeding of animals, made in 

 1847, 1848, and 1849, the results of which were published in the last-mentioned year 

 — we found that, in the case of succulent roots used as food, not only were they not 

 of value as food in proportion to their richness in nitrogen, but when the percentage 

 of it was higher than a certain normal amount, indicating relative succulence and 

 immaturity, they were positively injurious to the animals. So marked was the 

 variation of result according to the condition of maturity or otherwise of the 

 foods employed, that, when re^^ewing the results of the experiments which had up 



