160 THE ROTHAMSTED EXPERIMENTS. 



3. That free nitrogen is fixed in the course of the develop- 

 ment of the organisms within the nodules, and that the 

 resulting nitrogenous compounds are absorbed and utilised 

 by the host. 

 The most Certainly the balance of the evidence at present at command 

 likely ex- ^ g muc h j n f aV our of the third mode of explanation. Indeed 



planation. . . . r . * . . 



there seems nothing in the tacts to lead to the conclusion 

 that under the influence of the symbiosis the higher plant 

 itself is enabled to fix the free nitrogen of the air by its 

 leaves. Nor does the evidence point to the conclusion that 

 the nodule -organisms become distributed through the soil, 

 and there fix free nitrogen, the compounds of nitrogen so pro- 

 duced being taken up by the higher plant. It seems much 

 more consistent, both with the experimental results and with 

 general views, to suppose that the nodule-organisms fix free 

 nitrogen, and that the nitrogenous compounds produced are 

 absorbed and utilised by the plant. 



In other words, there does not seem to be any evidence 

 that the higher chlorophyllous plant itself fixes free nitrogen, 

 or that the fixation takes place within the soil ; but it is 

 much more probable that the lower organisms fix the free 

 nitrogen. If this should eventually be established, we have 

 to recognise a new power of living organisms — that of as- 

 similating an elementary substance. But this would only be 

 Lower or- an extension of the fact that lower organisms are capable of 

 gamsms performing assimilation-work which the higher cannot ac- 



servmg the r ,. , m ,.■,.., , , , r ;i • <• i 



higher. complish ; whilst it would be a further instance of lower 



organisms serving the higher. 

 Loew's Lastly, it may be observed that Loew has suggested that 



theory. the vegetable cell, with its active protoplasm, if in an 

 alkaline condition, may fix free nitrogen with the formation 

 of ammonium-nitrate. Without passing any judgment on 

 this point, it may be stated that it has frequently been found 

 at Rothamsted that the contents of the nodules have a weak 

 alkaline reaction when in apparently an active condition — 

 that is, while still flesh-red and glistening. 



It will be seen that the experimental results which have 

 been brought forward constitute only a small proportion of 

 those obtained at Eothamsted ; and it is hoped that when the 

 investigations and the study of them are completed, more 

 definite answers will be forthcoming to some of the admittedly 

 still open questions in connection with this interesting and 

 important subject. 



