184 J. H. Gilbert— Points in connection with Vegetation. 



of dust. Theodore de Saussure was the first to demonstrate 

 the presence of ammonia in the air, and consequently in 

 meteoric waters. Liebig 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, ami comprised within 

 limits, which nave <pn < entlv been indicated in the remark- 

 able investigations of .M, Si •! dosing.'' 



"(B.) From the soil, which, besides furnishing the crops 

 with mineral alkaline substances, provides them with 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 <-om!>b :-■ fertilizing 



by the effect of time. If we tab 



the_ deposits of the last geological period must be coi sid< n 1 as 

 an inexhaustible reserve of fertilizing agents. Forest-, prairies, 

 and some vineyards, have really no other manures than what 

 ished by the atmosphere, and by the soil. Since the 

 basis of all cultivated land contains materials capable of giving 

 rise to nitrogenous combinations, and to mineral .- 

 assimilable by plants, 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 nitrogen of the" atmosphere. As for 

 the absorption of the gaseous nitrogen of the air bv vegetable 

 earth, I am not acquainted with a single irreproachable'obser- 

 vation that establishes it; not only does the earth not absorb 

 itrogen, but it gives it off, as you have observed in 

 conjunction with Mr. Lawes, as Eeiset has shown in the case of 

 dung, as M. Schlosing and I have proved in our researches on 

 nitrification." 



" If there is one fact perfectly demonstrated in physiology, 

 it is this of the non-assimilation of free nitrogen bv plants: 

 and I may add by plants of an inferior order, such as myco- 

 derms, and mushrooms." 



Numerous experiments of Schlosing indicate a similar result 

 of Boussingault. He selected a soil rich in 

 humus, containing about 16 per cent of moisture, and 0263 

 per cent of combined nitrogen. Known quantities of it were 

 placed in large wide glass tubes, and during a period of about 

 four months, he aspirated over them air containing respec- 

 tively from l-o to 21 per cent of oxygen. He determined the 

 carbonic acid in tin ; ,ss _ „i ,,d t in, icid in the 



soil beiore and after the experiment He found that both the 

 combustion of the organic matter, and the formation of nitric 

 acid, were very considerable, even with the lowst proportion 

 of oxygen in the air; but that the formation of the nitric aeid 



