1890.] On the Question of the Fixation of Free Nitrogen. 101 



fine root-fibre not removed at the conclusion, so that where there is 

 loss it is to be supposed that some of the original nitrogen of the soil 

 has contributed to the growth. In the case of the garden soil, with 

 its high percentage of nitrogen, it is of course not impossible that 

 there may have been some loss by evolution of free nitrogen. 



That there is at any rate no material gain in the soils would seem 

 to be confirmatory of the conclusion indicated by other evidence, 

 that the fixation of nitrogen is not effected by the organisms within 

 the soil independently of the symbiotic growth of the nodules and 

 their contents and the higher plant to which they are attached, to 

 whose nitrogenous supply they seem to contribute. Indeed, if the 

 fixation had taken place under the influence of microbes within the 

 soil, independently of connexion with the higher plant, we should 

 have to conclude that the latter had, nevertheless, availed itself of 

 exactly the whole of the nitrogen so brought into combination — a 

 supposition for which there would seem no reasonable justification. 



Turning to the middle division of the table, which shows the nitro- 

 gen in the seed sown, in the total vegetable matter grown, and the 

 gain, and disregarding the changes in the soil itself, which it has been 

 seen may well be done, it will be observed that the gain of nitrogen in 

 the plants is so large as to be very far beyond the limit of any 

 possible experimental error. This certainly cannot be said of some 

 of the experiments conducted on other lines, the results of which 

 have been published in recent years, and been held to show the fixa- 

 tion of free nitrogen under the agency of micro-organisms within the 

 soil, without coincident higher plant-growth, or with the coincident 

 growth of other plants than of the leguminous family. 



The gain in these initiative experiments with peas is, however, 

 much less than in many of those of Hellriegel and Wilfarth. This is 

 not to be wondered at, when the late period of the season, and the 

 consequent character of the growth, are borne in mind ; and when we 

 come to consider the greater growth attained in the experiments of 

 1889, little doubt can be entertained that the fixation was then very 

 much greater than it was in 1888. 



To refer to the figures, it is seen that, whilst the nitrogen supplied 

 in the seed was only 0*03 gram or less, that of the products of growth 

 was 0-2822 gram in pot 1, 0'5361 in pot 2, 0'4357 in pot 3, and 0'6600 

 in pot 4 ; and the gains are ^ of a gram in pot 1, more than \ a gram 

 in pot 2, nearly \ a gram in pot 3, and more than \ a gram in pot 4. 



The third division of the table shows — the total nitrogen at the com- 

 mencement (in soil and seed together), at the conclusion (in soil and 

 total vegetable matter grown), and the gains. But the significance of 

 the results is more clearly seen in the last two columns. The first of 

 these shows the relation of the amount of nitrogen in the total 

 products (soil and plants together) to the total initial nitrogen (soil 



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