50 RESULTS OF EXPERIMENTS AT ROTHAMSTED, 



Wilfarth concluded that the Papilionacese can derive the whole of 

 their nitrogen from the air, but that it is doubtful whether the root- 

 nodules are connected with the fixation, though the results point to the 

 agency of bacteria in some way. 



In reference to these results, whilst it can hardly be said that there 

 is an unsolved problem in regard to the source of the nitrogen of our 

 w0ft-Leguminous crops, it must be admitted that, in spite of all the 

 investigations and discussions of the last 50 years, the source of the 

 whole of the nitrogen of our Leguminous crops has not been satis- 

 factorily explained by results obtained on the lines of inquiry until 

 recently adopted. Evidence obtained on new lines should, therefore, 

 receive careful consideration ; and there can be no doubt that, in 

 recent years, cumulative evidence has been adduced, indicating that 

 Chlorophyllous plants may avail themselves of nitrogen brought into 

 combination under the influence of lower organisms ; the development 

 and action of which would seem in some cases to be a coincident of 

 the growth of the higher plants to be benefited. But such a conclusion 

 is of such fundamental importance, that it seemed desirable it should 

 be confirmed by others. To some results obtained at Rothamsted in 

 this direction, I shall refer further on. 



So long ago as 1853, Professor Emil von Wolff obtained 6 times as 

 much dry produce of Clover, grown in an ignited rich meadow soil, as 

 in the same soil in its natural state. Thus, the increased growth, and 

 the increased assimilation of nitrogen, took place in a soil not only 

 nitrogen-free, but sterilised ; so that, unless micro-organisms were 

 acquired during growth, the supposition of their influence in fixing 

 free nitrogen would be excluded. 



Much more recently, Wolff has made numerous experiments, with 

 Oats, Potatoes, and various Papilionacese, in river-sand ; in some cases 

 unwashed, and in some washed ; in some without manure, in some 

 with purely mineral manure, and in some with nitrate in addition. 

 Accordantly with common experience, there was little increase in the 

 Oats or Potatoes with mineral, but much with nitrogenous manure ; 

 and, on the other hand, with the Papilionacese there was very marked 

 increase with the mineral manure, and but little more by adding 

 nitrate. In the experiments with Lupins, Beans, and Clover, in 

 unwashed sand, the results indicated gain of nitrogen, beyond that 

 probably due to the nitrogenous impurity in the sand ; but with sand- 

 Peas, grown in washed sand, which was assumed to be nitrogen-free, 

 the gains from some external source were unmistakable. 



As to the explanation, Wolff does not suppose that free nitrogen is 

 fixed by the plants themselves ; nor does he favour the view that it 

 was fixed by the agency of micro-organisms. The plants may take up 

 combined nitrogen from the air by their leaves ; but he thinks it more 

 probable that combined nitrogen is absorbed from the air by the soil, 

 and that free nitrogen is fixed within the soil under the influence of 

 porous and alkaline bodies. He admits that it is not explained why 

 Cereals do not benefit by these actions as well as Papilionacese ; and he 



