June r, 1894.J THE TROPICAL AGRICULTURIST. 
803 
RECENT INVESTIGATIONS AND IDEAS 
ON THE FIXATION OF NITROGEN 
BY PLANTS. 
Three totally diffe'ent, thoogh convergent, scientific 
CDnt.r< verges have arisen duriog the latter hslf of the 
present century conoernicg the role played in nature by 
nitrogen, as met with in the flir, rain, ard soil, fieo 
or combined, in connection with the ordinary plants 
of agricultu-e and forestry; and q'lite apirt from th ir 
real relations to one another, thefe three controversies 
h»va at times been somewhat cmifusad in their issir s. 
One of these controversies turned 01 the qu s'im 
of the tranti'orma'ions of combined nitrogen. »s met 
withintli3 forms of ammonia, nitritep, and nitra'es, 
and Bs organic compounds of nilrogon resulting from 
the decomposition of the remains of living beings — 
plants and animals — in the soil. The outcome hes 
been the p-oot that oxidatiois and da-oxilations of 
these compounds are intimately hound up wi h the 
physiol gical aolivitios of living organisms; ecp^cially 
bacteria, in the soil; the investigations of Giltay and 
AbersoD, and Wino^ridsky's brilliant researches es- 
pecially, bave brought wh»t hsd long been regarded 
as pureW ohRmical problems into the domain of bio- 
logy. "Nitritication " and "de-nitrification," to use 
the current term", are phenomena incorporated with 
those cf fermentation, respiration, &c., and theref jre 
involve biological science for their elucidation. 
Another of theee controversies turned on the ques- 
tion vfhether tbe free introgen which fi rms so large 
a proportion of that huge gnseous ocean, the at- 
mosphere, can be again directly employed by green 
leave', and boilt up »a combined nitrogen in plints ; 
or whether, once having besn disengaged from or- 
ganic and other compoundp, and pass;d into the a'r 
as gaseous nitrogen, it is for ever lost, except in so 
far as electric di cUargfs an 1 other energetic physical 
and chemical procesfei force this reUtiv»ly inert 
element into combinations, which tt e rain then brings 
down BS inorganio s its, and so help to restore the 
balance of i.itrogenous substaLCS in the soil. 
This controversy, a long and iovolved one, started 
and for Eorae time continued as a peculiarly chemical 
qaestion, has pissed through various phases a.d 
branched out into several subsidiary controversiee, 
if wa may fo tsrm them. 
Thus the alleged " fi.xatioa " in the soilj (spjci .Hy 
investiga'ei by B rthelot and Andre, bocirae a 
scient'fic question apparently on definite lines of itj 
own, and (so f»r as any such q-iestim oaa be in- 
depondent) independent of the question whether 
ordinary green-lenfed plant?, such as peas, luceri:e, 
wheat, &c. c»n assimilate the free nitrogen of the 
atmosphere by processes more or less compara'de to 
those by which they are known to assimilate the 
carbon they wrench from the carbon-dioxide of that 
gaseous environment. 
r.fThe latter question, r^.iin, becime a divided one, 
cMeflv owing to assertions thit grcn leaves could 
directly assimi'ate the ammonia, if no', the free nitrogen, 
of the air, and some time was occupied in arriving 
at the conclusion that ordinary grceu plants do not 
di octly asjimilato f r fix cither thg giseous ammo .ia 
or the tri e nitrogen of the atmosphere. Tliis con- 
clusion, in opposition to that arrived at by ViUo, 
was regarded as so thoroughly established by the 
experiments of IJaussing lult and of Lawes, Gilbert, 
aad Pugb, that it h"s been definitely accepted Riid 
taught for luMiy years — and rightly so, from the 
ev dtnce to hand. 
The thiid of tho three cont over ios referred tout 
the cu'set, is the more rejent oje coticernod with 
the quesii m whether cortsiu of the th-! liig lOr gri en- 
1 uf«d pUintp, pu ticulirly those known as leguminous 
p'a:.ts (^uch as peas, b ais, clovers, votclie.", lup ii", 
riiblnii itc ), wlmn living us thoy iionniiUy (!» iu 
.s; lubio' c :nd( cihl'ou with c rtxin luicr tcopi 5 and 
HBSOnliuUy pirasitio luiigoid ortjanisms whioli jnvalo 
t'loir rout', mo dilfcTontly pli cod fioiii other n'meu 
ulunts x* rt'gards th 1 pivor of " fuing " and iiaaiini- 
liitiig, iho froo Litrot.e i of iho atiuojphare. 
The prefent po'dt'nn of opinions on this hst and 
most remarkable controversy is the snbjeot of this 
article, so far as it can be done jiistico to in the 
short space at ilisno^al. 
It in now well known tb^.' leguminous plants ara 
normally found to have certi'n rio''osities or fw llings 
on their roots, and that tho«e swellings are cau«ed 
by the activity ot' cftrtf in minute trganisms which, 
as tho writer of this «r icle firit proved, invade the 
roots from cutnde, after the manner of a pirasitic 
fungus. The co-jtrovorsy as to the exact nature of 
these organisiin — bscteria, accori'ing to Prazmowaki, 
B'^yeriock, and others, degraded allies tf the Ustila- 
ginese, or some lower fungus, according to my obser- 
vations, and the confirmatory evid^nco of Laurent — 
in no way affects the trnUi tint tlieso org-anisms 
do not kill the plants attacked, or even make th'-m 
diseased, but incite them to more active life for a 
t"me. The ev"dence on which these organisms (termed 
" bacteroids ") have been taken tc be ba-teria — ^their 
growth in gelatine tubes s'aini g, and th':-ir roinu'e 
size — :s (qaally in favour of tb^ir beina; lower fungi, 
and is no'; euflRaienUy conclusive. Eventually the 
nu'ri'ious contents of these nodul s, with the symbiolio 
" bacteriod.":," are absorbed, in whale rr in part, by 
the leguminous plant, and th'ir rich stores of citro- 
geHOUs material assimilated by the latter. 
The experiments of Hellriegel and Wilfarth, of 
L»wes andj Gilbert, and of others and myself, place l 
it beyond reasonable doubt that, taking th? legumi- 
nous plants and its symbiotic organ-sms together 
with the pot of soil in which it is grown as a 
closed 9y>tem, this system ooiitains more nitrog n at 
the entt of several wreks f'an can be acc uotet f r 
by the nitrogen in the soil aud the s^idit the com- 
mencement of the experiment : ard this was true in 
cases where OTefnl precauti uis were taken to pre- 
vent the aldit'on rf any li'rogen further than the 
free oilrnge 1 of tbe air. Ttie oi ly legitimate con- 
clusion wxs thiit fomewbere, ai d somehow, the sys- 
teti fixes free nitrogen from the air. 
Ti-is m»-(tjr has been since carried further, how. 
ever, by Laurent aud Schloesini?, wli"", by growing 
vari us pi mts in an air-tight apparatus urder sucti 
p rfect control that they could an=.lyse the quan iiy 
of nitrogen both in the plxnt and sjil, and in the 
purified air, sliowed that the g in of nitrogen in 
t' e formtr during the progress of tbe exp rlments, 
is balanced by a correspondiug 1 ss in the latter. They 
further sfaowtd that only two kinds of plants could 
thus 'fix" the nitrogen of the air. These are 1 gaminons 
plan s, and certain low.r algaa (perhips mixe 1 w th 
bacteria) or allied firms. This fixation only occurs 
mder certain definite cocdi ious m- reover. The legu- 
minnns plants must be infjcted with the sjmbiot'c 
"bacteroids," and the algae must be exposed freely 
to tho air and light in the apparatus: ev n a thin 
layer of tin steriliseel sand etuplojed sufficid to stop 
the action of the algse. 
Liaurent and Schloosing found no fixation in the 
ca'e of artichoke, oats, tobacco, mustard cress, or 
any other plants exprriincnted with ; and their ex- 
p^rimsnls, taken as crowntnij the edifice of evidence 
accumulated by them and numerous other observers, 
bave been fairly regarded as proving that 1 gmninous 
plants, at auy rate, and p' rliapi certa u lower algae, 
do somohow •' fix " the fieo nitrogen of tho at- 
moschere and assimilate it. 
Koch and Kossowitsch have recently elaimod to 
confirm tho above results of Laurent and Sch'oesing 
with algse, and it shou'd be nientionel that Prank 
had previously stated that such fixation by lower 
cryptogams o cura. Unfortunately we ara as yet 
uuinfornied what species of algaj are exactly con- 
cerned here, aud no one lias cultivated them pure 
aud confirm. d the results. 
U will be noticed that, s-) far. all that is estab- 
lished is that tho inf ctod leguminous plants, and 
the algio of sorts, jiliis tho Umiun soil (usually 
slerlised sand to which known additions are inad»v. 
somewhere and somehow gain in nitrogen at tho 
expense of the free nitrogen of Ihc atmosphere. 
