1890.] On the Question of the Fixation of Free Nitrogen, 117 



tion, the actually ascertained large gain of nitrogen by the leguminous 

 plant growing in a nitrogen-free, but properly infected, soil becomes 

 intelligible. It is admitted, however, that further investigation of 

 the mode of life of the parasite, especially having regard to its sur- 

 rounding media, is needed. 



It seems to us that there is nothing in the evidence pointing to the 

 conclusion that the fixation is effected by the lower organisms within 

 the soil independently of the symbiotic life. We do not here enter 

 into the question, so much discussed of late, as to whether or not there 

 is fixation within the soil under the influence of other low organisms, 

 independently of the associated growth of a higher plant. 



In our recent paper in the ' Philosophical Transactions,' before 

 referred to, we said that whilst experience, whether practical or 

 experimental, did not point to an unsolved problem in the matter of 

 the sources of the nitrogen of the agricultural plants of other families, 

 it was far otherwise so far as those of the Papilionaceee were con- 

 cerned. Further, that since the question of the sources of the nitrogen 

 of the Leguminosee had been the subject of experiment and of con- 

 troversy for about- half a century, and it was admitted that all the 

 evidence that had been acquired on lines of inquiry previously fol- 

 lowed had failed to solve the problem conclusively, it should not 

 excite surprise that new light should come from a new line of 

 inquiry; and, that hence should be recognised the importance of the 

 cumulative evidence of the last few years, of which that furnished by 

 the experiments of Hellriegel and Wilfarth was certainly the most 

 definite and the most striking, pointing to the conclusion that although 

 chlorophyllous plants might 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 was, apparently, in some cases a coincident of the growth 

 of the higher plant whose nutrition they were to serve. It was 

 added, that as such a conclusion was of fundamental and far- 

 reaching importance, it was desirable it should be confirmed by in- 

 dependent investigation. 



The results even so far obtained, and recorded in this paper, can 

 leave no doubt that this important conclusion is confirmed, so far 

 as a number of agricultural plants of the leguminous family are 

 concerned. The question suggests itself, whether such, or allied 

 agency, comes into play in the nitrogen assimilation of leguminous 

 plants generally, or of that of other than the agricultural representa- 

 tives of the non-legaminous families to which we owe such plants, 

 or of those of the numerous and varied other families of the vegetable 

 kingdom. 



It is true that the families which contribute staple agricultural 

 plants are but few, and that the agricultural representatives of those 



K 2 



