jukE I, 1894.] THE TROPICAL AGRICULTURIST. 
805 
regard the qaestion of fixation of free nitrogen by 
soil organisms, it is perfectly clear that here ia a 
most pressing question for further experimental 
research, and agricultural and forest practice are 
alike keenly interested in having the question defi- 
nitely answered. 
The third possible view — that the leguminosae are 
able to force free nitrogen iuto conibiuitiou with 
other elements, owing to the energetic action ot 
their protoplasmic machinery stimulated by the 
symbiotic fungoid organism — deserves more consider- 
ation than may at first sight appear, especially to 
these who are not familiarised with the remarkable 
phenomena of symbiosis generally. 
In the tirst place, tlie fact that leguminous plants 
amply provided with the root-nodules do " lix " the 
atmospheric nitrogen under conditions in which the 
same plants devoid of the nodules fail to increase 
their t-upplies of nitrogen, is far better established 
tha-i any 1 f the other cases discussed, and must now 
be accepted as proved by the experiments of Frank, 
Hellriegel, myself, Lavves and Gilbert, and especially 
by the recent splendid investigations of Laurent and 
Schloesing. 
It is true that Fr.ink says the symbiosis is not 
absolutely nece.-sary for the fixation to proceed, but 
even he deckxres that the leguminosae are .••timulated 
to greater powers of nitrogen-fixation by the nodule- 
organisms. 
A curious and significant confirmation of the 
symbiosis theory comes from the experiments of 
Nobbe, Schmid, Hiltner, and Hotter, who find that 
Elmarjnas plants, the root of which develop nodules 
due to the invasion of a fungus totally different from 
the one causing the leguminous nodules, also "fix" 
r.ud assimilate the free nitrogen of the atmosphere, 
as shown by their growing and flourishing much 
better and more rapidly than Edrainms plants side 
by side with them, but not infected with the root 
organism. It will be interesting to see if further 
research shows similar results with any of the 
physiologically similar root outgrowths, due to very 
different fungi, met with in Taxodimn, Podorarpiif, 
Alnm, Juiicv.>i, and many other plants .including 
some vascular Ciyptogams. 
Now comes the question, in what part of the legu- 
minous plant does the actual " fixation" of the free 
nitrogen occur ? Frank stands practically alone in 
claiming the leaves to be the organs concerned. 
Nearly all other observers regard the roots as 
the region, and the nodules tbemse ves as the actual 
seat of fixation. 
Kossowitsch has even attempted the heroic task 
of deciding be ween leaves and ro 'ts, by enclosing 
the former or the latter respectively in air- 
tight receptacles, shut olf from the non-enclosed 
parts, in which gases devoid of nitrogen were cir- 
culated. He could not always keep the apparatus 
perfectly gas-tight, however, and this and other 
failures met with in these exceedingly difficult ex- 
periments, undoubtedly weakens the force of his 
conclusions that it is in the roots and not in the 
leaves that the process occurs, though it does look 
as if the balance of evidence obtained fairly support 
his conclusion so far as it goes. 
There arc facts, however, to be gathered from 
the microscopic analyses of the root-nodules, as fur- 
nished by myself and others, which have been in 
great part overlooked in the discussions on this sub- 
ject, and which, although not conclusive, seem to 
support the view that the seat of fixation may be 
in tho nodules themselves. For instance, the nodules 
are supplied with a regular system of conducting 
vascular bundles, conmuinicating «ilh those of the 
roots; then their cells, during tho pe iod of incu- 
bation of the symbiotic organism, arc abundantly 
supplied with starch; further, the cells in which 
the fungoid organi.^iui is vigorously nourishing are 
evidently exceedingly active, as may be deduced from 
thoir large size, brilliant nuclei, protoplasm, and siip- 
vacuolc, all of which show signs of intense metabolic 
activity, lasting for considerable periods. The fact 
that tlie sap cxpiesscd from those active tissues ia 
alkaline, has been interpreted as in accordance with 
JjWws suggestion that the living protopla'jm, in 
presence of an alkali and free nitrogen, can build 
up ammonium nitrite, or some similar body. Be 
this as it may, there can be no question as regards 
the infected nodule-cells being centres where intense 
physiological activity is going on ; and it seems im- 
possible to avoid tho conclusion that the vascular 
supplies from the roots into tho nodules bring to 
these cells water in which various salts, carbo-hy- 
drates, &c. are dissolved, and carry off from them 
the soluble products of metabolism. 
Presumably these products of metabolism include 
nitrogenou.s bodi(g. 
In the ordmary courso of evcntp, theory ttaohos 
that ih'fe nitrogenou.-i bodies— f.f/., nmidep, pr<c d;d 
by t i '1 pier c imp juud; — are built up ty the machinery 
of ihe ordinaiy living oell-protopl sm from carbo- 
hjdratea and mtratee, the ercrgy neceeeary for the 
mttaboli m bi iu>^ dirived chittty (if ntt entir.^Iy) 
byt' e oxidation of part of the carbo-hydrates supplied. 
Th s coaslrmlive metabolic work of the protoplasm 
is an act which we cannot fxplain in detail. We 
c in only illmly perc. ive thnt it auU be due to 
81 me remiirkible power the profopUf^m po.sses'es — 
in virtue of wLich it is an illimitrblo midline much 
more rconomictl in its actions than any npparatua 
we cnn conatruct — of so p'aciug the atoaia pna mole- 
cuks of the nitia'e, carbo-hydrate, h ater, &e. with 
which it works, that they are euab'e to undergo 
movements into which we cannot as yet force them 
in the laboratory. 
The whole matter seems to depend on some parti- 
cular mode of presentment of the atoms and mole- 
cules concerned ; and we can see no further than 
that this can be done in the living cell, because the 
protoplasm is a suitable engine for thus bringing 
the combining elements into the necessary positions 
in space. 
Now, if this is so, their seems no exclusion of 
the posoibility, at any ra e, tbat the cell-machinery 
may be so stimulated into greater activity that it 
can even force the notoriously inert nitrogen mole- 
cules, properly presented, into combinations with 
other molecules, resulting in the produa ion of nitritef=, 
amides, or similar bodies in ascending order. 
The whole matter no doubt revolves itself into 
some such question of a properly adopted engine 
sniiiciently supplied with enei'gy. The matter seems 
capable of explanation, in some degree, if we re- 
member that carbo-hydrates and oxygen are present 
in abundance ; the real difficulty is with the machinerj-, 
for we cannot as yet picture the exact construction 
or working of such an engine, as physiology neverth- 
less impels us to suppose tbe cell-protoplasm must be. 
It may be remarked, by the way, that the like-^ 
uess of the living protoplasm to an engine, in the 
sense implied, may hold good whether the former 
is an " emulsion," in the sense of the defenders of 
that hypothesis, or a " structure, ' in the sense of 
those who refuse the emidsion hypothesis. 
The fourth of the possible views as to the means 
by which free nitrogen becomes available to the 
leguminous plant, however, reminds us that, although 
the evidence points to the stiniulated leguminous 
plant as the best established example of one capable 
of doing this work, there are other possibilities. 
Berthelot's recent instance that certain soil-bacteria 
can fix free nitrogen, taken with Frank's, Laurent 
and fcjchloosing's and Koch and Kossowitsch's experi- 
ments, make U impossible to deny that the above 
hypothesis as to the powers of the protoplasmic 
machinery many appl)' to the cells of some lower 
organisms, without symbiosis coming into play at 
all. Tho remarkable facts brought to light regard- 
ing sulphur-bacteria and irou-baoteria by Wino- 
gradsky, and tlie still more unexpected results this 
observer obtained with nitrifying organisms, show 
that the machinery of the cell can avail itself of 
sources of energy undreamt of by earlier observers. 
If, by the oxidation of sulphur or sulphuretted hy- 
drogen, or of lower iron-compounds, or of ammonia, 
certain of these organisms can obtain thu energy 
necessary to set going machinery capable of so 
presenting other molecules of the eleiiionta they lake 
up to one another that organic compoundj result, it 
i-i by no means iuoon«eivable that, at the cost ()i 
