Nov., 1892. the fixation of atmospheric nitrogen. 
257 
extract was used there was, almost always, luxuriant growth 
and abundant formation of root - nodules, but where the 
extract had been sterilised, the plants were meagre and ill- 
grown as before. These experiments were conducted princi¬ 
pally with peas, beans, or vetches, but further trials showed 
that in the case of lupins similar results might be obtained 
by watering with an appropriate extract derived from soil 
in which those plants were growing, though the extract 
which was so successful in the case of peas was without effect 
in that of the other plants named. A curious point is 
thus raised as to the existence of varieties or species of 
microbes.appropriate to each plant. Hellriegel and Wilfarth’s 
experiments were repeated later by Gilbert and Lawes, 
and confirmed in every particular; they also determined 
the nitrogen actually present in the crops under the 
different conditions, and found that, without soil extract, 
and in the absence of nodules, there was no gain of nitrogen, 
but that with soil extract, and consequent nodule formation, 
there was many times as much nitrogen in the produce as in 
the seed sown, and the conclusion drawn was that atmospheric 
nitrogen must have been fixed by the plant, and that this took 
place in the course of the development of the organisms 
within the nodules, the resulting nitrogenous compounds 
being absorbed and utilized by the host. Within the last 
year MM. Schloesing, fils, and Emile Laurent have pub¬ 
lished researches which prove that the power of fixing free 
nitrogen is not confined to the Leguminosse, but that some of 
the “inferior green plants” (mosses and algae) possess the 
same property. The commensalism or symbiosis in which the 
organism of the nodule supplies the host plant with food, in 
the shape of nitrogenous compounds, throws light upon, and at 
the same time helps to confirm, the views of Schwendener, 
and, after him, of De Bary, with regard to the nature of 
lichens. Indeed, one objection to those views on the part of 
biologists lay in the fact that no analogous instance could be 
found in nature. Schwendener teaches that every lichen is a 
compound organism, consisting of a fungus and an alga, 
which bear to each other somewhat the same relation as 
a tree to its leaves ; the fungus supplies the nitrogenous 
matter to the alga, while the alga, by means of its chlorophyll, 
builds up carbohydrates for the support of the fungus out of 
the carbonic acid of the atmosphere. We see here a very 
close and suggestive analogy to the case of a leguminous 
plant and its nitrogen-fixing nodules. 
[Our readers will fiud much interesting matter for reflection on the 
subject of this paper in a valuable contribution by Prof. Percy F. 
Frankland, F.R.S., read before the Royal Institution of Great Britain, 
printed in “ Nature,” June 9th, 1892. —Eds. “ Mid. Nat.”] 
