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



subsequently obtained increased growth by seeding with extract from 

 both a loamy humus-soil, and a root-crop-soil ; but the result was less 

 marked than with some other Leguminosae. It has been seen that, in 

 the first year of the experimental growth of clover at Rothamsted, no 

 beneficial effect resulted from seeding with rich garden-soil-extract. 

 It is believed, however, that the growth in the sterilised sand without 

 soil-extract seeding will prove to be greater than can be accounted for 

 by the supply of nitrogen in the seed sown. If this should turn out 

 to be the case, the supposition will be that the necessary infection has 

 come from the atmosphere. In reference to this point it may be men- 

 tioned that the glass-house in which the experiments are conducted 

 Stands in the midst of allotment gardens, in which a great variety of 

 vegetables is growing, whilst Hellriegel's most definite result with 

 clover was obtained by seeding with an extract from a root-crop 

 soil. 



Existing evidence is, therefore, in favour of the supposition that 

 red clover does derive some of its nitrogen from fixation under the 

 influence of proper soil-infection, and the resulting symbiosis of the 

 lower and the higher growth. There is, however, at present very 

 little definite evidence to guide us in judging under what conditions, 

 on the one hand soil supplies of combined nitrogen, and, on the 

 other such fixation, will contribute more or less of the total nitrogen 

 of the crop. As one important element in forming a judgment on the 

 subject, it is, as already said, our intention to study the conditions 

 under which the development of nodules on the roots of growing 

 clover is more or less favoured. 



Upon the whole, then, the evidence at command points to the con- 

 clusion that, in the case of most if not all of our leguminous crops, 

 a greater or less proportion of their nitrogen will be due to the 

 fixation supposed. 



Admitting the fact of such fixation to be fully established, the 

 question still remains, how is it to be explained ? Unfortunately, 

 here again, as in the matter of the importance to agriculture in a 

 quantitative sense, of this source of nitrogen to our crops, there is 

 much yet to learn before a satisfactory answer can be given. Hell- 

 riegel frankly admits that a satisfactory explanation is still want- 

 ing ; and we agree with him that we must know more of the nature 

 and mode of life of the organisms which, in symbiosis with the 

 leguminous plant, bring about the fixation of free nitrogen, before 

 the nature of the action can be understood. As to the mode of life 

 of these bodies, we owe much to the investigations of Marshall Ward, 

 Prazmowski, Beyerinck, and others ; but probably none will more 

 readily admit than themselves, that the facts which they have estab- 

 lished so far, are insufficient to afford an adequate explanation of 

 the phenomena involved. 



