86 



Sir J. B. Lawes and Prof. J. H. Gilbert. [Jan. 9, 



and at Rothanisted, under conditions in which the action both of elec- 

 tricity and of microbes was excluded, were conclusive against the sup- 

 position that, under such conditions, the higher chlorophyll ous plants 

 can directly fix the free nitrogen of the atmosphere, either by their 

 leaves or otherwise. Others have, indeed, come to the conclusion 

 that at any rate some plants do directly fix the free nitrogen of the 

 air by their leaves. We believe, however, that there is, up to the 

 present time, no evidence which can be held to be conclusive in favour 

 of such a view. 



It was pointed out how large was the store of already existing com- 

 bined nitrogen in many soils and subsoils, and evidence was adduced to 

 show that even Leguminosce derive, at any rate a considerable amount 

 of nitrogen from nitric acid within the soil and subsoil ; and, further, 

 that it was, as a rule, those having the most powerful root-develop- 

 nieni that took up the most nitrogen from somewhere ; and it was 

 considered that this fact pointed to a subsoil source. 



Upon the whole it was concluded that, at any rate in the case of 

 our gramineous, our cruciferous, our chenopodiaceous, and our solane- 

 ous crops, atmospheric nitrogen was not the source. It was admitted, 

 however, that existing evidence was insufficient to explain the source 

 of the whole of the nitrogen of the Leguminosce. 



According to some of the more recent experimenters, the fixation 

 of free nitrogen is not limited to our leguminous crops ; and the 

 modes of explanation of the gains of nitrogen observed are extremely 

 various. Thus, it is assumed — that combined nitrogen has been 

 absorbed from the air, either by the soil or by the plant ; that there is 

 fixation of free nitrogen within the soil by the agency of porous and 

 alkaline bodies; that there is fixation by the plant itself ; that there 

 is fixation within the soil by the agency of electricity ; and, finally, 

 that there is fixation under the influence of micro-organisms within 

 the soil, with, or even without, the accompanying growth of higher 

 plants. 



The balance of the evidence recorded seemed to be undoubtedly in 

 favour of the supposition that there is fixation under the influence of 

 micro-organisms or of other low forms within the soil, and of all the 

 various results which were discussed, those of Hellriegel andWiifarth 

 were considered to be by far the most definite and significant ; point- 

 ing to the conclusion that, although the higher chlorophyllous plants 

 may not directly utilise the free nitrogen of the air, some of them, at 

 any rate, may acquire nitrogen brought into combination under the 

 influence of lower organisms, the development of which is, appa- 

 rently, in some cases, a coincident of the growth of the higher plant 

 whcse nutrition they are to serve. Such a conclusion is, however, of 

 such fundamental importance that it seemed very desirable that it 

 should be confirmed by independent investigation. 



