The Smirces of the Nitror/en of wr Leguminovs Crops. 695 
the earlier formed nodules become exhausted, others are con- 
stantly produced, thus providing for future growth. The results 
of this new series of experiments, taken together with those of 
the quantitative series, serve farther to show that there is inti- 
mate connection between the gain of nitrogen by Leijuminosce 
and the development of nodules on their roots. 
The alternative ex]^)lanations of the fixation of free nitrogen 
seem to be — 
1. That, under the conditions of the symbiosis, the plant is 
enabled to fix the free nitrogen of the atmosphere by its leaves. 
2. That the nodule-organisms become distributed within the 
soil, and there fix free nitrogen ; the resulting nitrogenous com- 
pounds becoming available as a source of nitrogen to the roots 
of the higher plant. 
3. That fi-ee 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. 
It certainly seems to us that the balance of the evidence at 
present at command is much in favour of the third mode of ex- 
planation. Indeed, there seems little or nothing in the facts 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-bacteria become distiibuted through the soil 
and there fix free nitrogen, the compounds of nitrogen there 
produced being taken up by the higher plant. It seems more 
consistent, both with the experimental results, and with general 
views, to suppose that the nodule-bacteria fix fi'ee nitrogen 
within the higher plant, 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 eventu- 
ally be established, we have to recognise a new power 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 
cannot accomplish ; whilst 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, may fix free 
nitrogen with the formation of ammonium nitrite. Without 
passing any judgment on this point, it may be stated that it has 
frequently been found at Rothamsted that the contents of the 
