333 



nodules at the conclutsioii. Still, as in the peas grown in siiiul, tlio 

 porcentage of nitrogen in the dry substance of the nodules was very 

 much reduced at the conclusion. In the case of tlic ]»lant of longer life — 

 the sainfoin — there was, both in sand and in soil, very great increase in 

 the number of nodules and also in the actual amount of dry substance 

 and of nitrogen in them as the groAvth progressed. The percentage of 

 nitrogen in the dry substance of the nodules also showed, even in the 

 sand, comparatively little reduction, and in soil even an increase. In 

 fact, separate analyses of nodules of difi'erent character or in different 

 conditions showed that while some were more or less exliausted and 

 contained a low x><ii"eentage of nitrogen, others contained a high per- 

 centage and were doubtless new and active. Thus the results pointed 

 to the interesting conclusion that although with the jdant of longer life 

 the earlier-formed nodules became exliausted, others were constantly 

 produced to provide for future growth. 



As to the exj)lanation of the fixation of free nitrogen, the facts at 

 command did not favor the conclusion that under the influence of the 

 symbiosis the higher plant itself was enabled to fix the free nitrogen of 

 the air by its leaves; nor did the evidence point to the conclusion that 

 the nodule bacteria became distributed through tlie soil and there fixed 

 free nitrogen, the compounds of nitrogen so produced being taken up by 

 the higher plant. It seemed more consistent, both with experimental 

 results and with general ideas, to suppose that the noduh; bacteria 

 fixed free nitrogen within the plant, and that the higher i)laut absorbed 

 the nitrogenous compounds produced. In other words, there was no evi- 

 dence that the chlorophyllous plant itself fixed free nitrogen, or that 

 the fixation takes place within the soil, but it was more probable that 

 the lower organisms fix the free nitrogen. If this should eventually be 

 established we have to recognize a new x>ower of living organisms — 

 that of assimilating an elementary substance. But this would only be 

 an extension of the fact that lower organisms are capable of performing 

 assimilation work which the higher can not accomplish, w^hile it would 

 be a further instance of lower organisms serving the higher. Finally 

 it may here be observed that Loew has suggested that the vegetable 

 cell with its active protoplasm, if in an alkaline condition, might fix free 

 nitrogen, with the formation of ammonium nitrate. Without passing 

 any judgment on this jwint, it may be stated that it has frequently been 

 found at Kothamsted 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. 



As to the importance of the fixation for agriculture and for M'geta- 

 tiou generally, there is also much yet to learn. It is obvious that 

 different Papilionaceae, growing under the same external conditifms, 

 manifest very different susceptil)ility to or power to take advantage of 

 the symbiosis, and under its influencemay gain much nitrogen. This is of 

 interest from a scientific point of view as serving to explain the souice of 



