248 SCIENCE PROGRESS 



after Gilbert's death in fact — other bacteria were discovered 

 living free in the soil which also possess the power of fixing 

 nitrogen and some of the evidence accumulated at Rothamsted 

 served to demonstrate that it is to these later bacteria we must 

 attribute the storing up of nitrogen which has been going on 

 for long ages in some of the rich virgin soils, such as the black 

 lands of Manitoba and Russia. Even the temporary putting 

 down of land to grass and any other farming process which will 

 enrich the soil with carbonaceous matter leads to the fixation 

 of nitrogen, by providing material from which the appropriate 

 bacteria can derive energy. Thus, in a very wide sense, Liebig's 

 opinion is vindicated : the growth of plants, though not of the 

 higher plants, is the only method by which any considerable 

 amount of nitrogen is brought into combination in nature 

 and it is possible to devise a system of farming which will 

 continue to produce good crops without any extraneous sources 

 of nitrogen, provided the land be supplied with lime, phosphoric 

 acid and potash. 



With the first twenty years of the field trials, a period which 

 was sufficiently long to eliminate the experimental error and 

 to smooth out the inequalities due to varying seasons, it might 

 have been considered that the original Rothamsted experiments 

 had done their work ; it is indeed true that, as regards the im- 

 mediate effect of the application of the manures to the crops, 

 final conclusions had been reached of which no revision has been 

 necessary. But here comes in one of the chief contributions of 

 Gilbert to the Rothamsted Station. Possessed of a conservative 

 temperament and persuaded that much still remained to be 

 learnt, he held out for the continuance of the- experiments 

 without change ; as a result, the treatment of the plots has been 

 repeated without variation from at least 1852 until the present 

 day. Thanks to this continuity, the Station now possesses 

 unrivalled material for the study of a number of questions which 

 were hardly appreciated or even suspected at the time the 

 experiments were designed ; in fact, there is hardly any portion 

 of the theory of nutrition of the plant which they do not 

 serve to elucidate. It is even to-day impossible to guess in 

 what directions they may not next prove to be of value; as 

 new points of view and lines of research successively open 

 before us, they will doubtless provide material for investigation, 

 either from the past records or the crops actually growing. A 



