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ON

THE SOURCES OF

THE

Were hOGEN OF VEGETATION;

WITH SPECIAL REFERENCE TO THE QUESTION WHETHER PLANTS

ASSIMILATE FREE OR UNCOMBINED NITROGEN.

BY
JOHN BENNETT LAWES, F.R.S., F.CS.,
JOSEPH HENRY GILBERT, Pu.D., F.R.S., F.CS.,

AND
EVAN PUGH, Ps.D.,-F.C.S.

From the PHILOSOPHICAL TRANSACTIONS.—Parv IT. 1861.

LONDON:
PRINTED BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET.
1862.

ON

PALE... SO; Ue Cai sea cer:

THE

NITROGEN Of YEG a eee,

WITH SPECIAL REFERENCE TO THE QUESTION WHETHER PLANTS

ASSIMILATE FREE OR UNCOMBINED NITROGEN.

LIBRARY
NEW YORK
EOTANIC AL
GARDEN
BY
JOHN BENNET LAWES, F.R.S., F.C.S.,

JOSEPH HENRY GILBERT, Pu.D., F.RS., F.CS.,
AND
EVAN PUGH, Ps.D., F.C.

From the PHILOSOPHICAL TRANSACTIONS.—Panrr II. 1861.

LONDON:
PRINTED BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET.
1862.

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,

JAN 28 1904

[ 431 ]

XXIII. On the Sources of the Nitrogen of Vegetation; with special reference to the
Question whether Plants assimilate Free or uncombined Nitrogen. By Joux Benner
Lawes, F.R.S., F.C.S., Josepx Henry Ginpert, PA.D., PRS. F.CS., and Evay
Pueu, Ph.D., FCS.

. Received June 21,—Read June 21, 1860.

CoNnTENTS.

PARE BRS.

GENERAL HISTORY, AND STATEMENT OF THE QUESTION,
Page
Szorron J.—Jntroduction, and carly History ......cccseecsececsenseoceesseqecseovsecccecserecsesesceseees 4393-430
Section I1.—Annual yield of Nitrogen per acre, in different Crops :—
A. Yield of Nitrogen per acre when the same crop is grown year after year, on

the same land . De cesaivecis 435—438
B. Yield of RABatSon aor acre i ae Wheat i is grown in * aibenantion with Beats:
or with Fallow seguiccadsevicasieesucetroaaaeeneceetessier ess 438—439

C. Yield of Nitrogen per acre re crops are grown in an valpa anal course See Raletiten 439—44.0
D. Relation of the increased yield of Nitrogen in the produce, to the amount sup-
plied, when nitrogenous manures are employed .........s.ssceseeseeseeeeesesseneee 440—442

Section II].— General view of the various actual or possible sources of the Nitrogen of our crops :—
Enumeration of, observations; &C. ..........s..0eeessessencoecsssesccssccseccccecsccscsccseeee A42—447,

Srorron 1V.—Review of the Researches of others, on the question of the assimilation of Free
Nitrogen by Plants, and on some allied points :—

Introductory observations *. des SUSI. ARS Area Desa aataeesteen AAT
A. The Experiments of M. Recents SS decb 0dr CCHOCOIAACHOGIDGIO canutioadontncbocodds GHss a
B. The Experiments of M. G. VILLE ......... yee oD—463
Summary statement of the Results, and dondlisions} “of M. Houser aud
M.:G. VILLE ........: oa bbanoSadhesles tad obetwlatadth Rekvekestueiavecsneemteess (SOR ——kiG4
C. The Experiments of M. Maines SERN EN SROs Sialic et Gaaatoates esteneacewes, AGA
DMhelviews OL VeRO Wea. eetcaveseeseakc eds teeta ook cee cam auiecaiostinenechitaticeebne sine siccencia ss 464—465
EB... The Experiments. of MM. Cronz and GRATIOLET ....c.ecesesseesesceresesceeseceeens 465
H,. The Experiments. of Mi DE WUUGA Te. cccc-ceccaeccesecaccevsvedsesieveliecstevesaveersssees | 200-400
G. Dhe' Bxperiments| of Mi HARING) (iccscscescco+sosseccuceesursecssearpasssensaceereassao OO
Hi. Experiments recorded by M. A. Bunmioi, ScdanpoNdoacCAH odjONd coanNSOSACEHacBeeoneT 467
Concluding observations ....csccscssseecsscseavevecseetonsaeeesesesceses-ceccssensessecees 467—468

PART SECOND.

EXPERIMENTAL RESULTS OBTAINED AT ROTHAMSTED, DURING THE YEARS 1857,
1858, AND 1859.
Tntroductory ODServations secsscssecsecenccncecececccececccnscnsensnsesaeessnaanceeseeccsecceecnenseesea senses ees 468—470
Srcrioy I.—Conditions required, and Plan adopted, in Experiments on the Question of the assi-
milation of Free Nitrogen by Plants :—
A. Preparation of the soil, or Matrix, for the reception of the Plant, and of the
nutriment to be supplied to it .......s:sssssssesesssreeecessessesseeserscssserssers 470—472

MDCCCLXI. 30

432 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

B. The Mineral Constituents added to the aie BOLLS en dcevvecsnconasvatnadaveste

C. The Distilled Water .......... Tavenarvses veordiuadoeea

D. The Pots used to receive the Soil, ashy ‘Plant, vio. vatedasebreeasva

E. Final preparation of the Soil, Ash, and Pot, for the Plant ;

Hs, “Lhe Pecos waAKeN 100 EXPCTIMIOMl ...,s1<ss.sensapveseswsvecesgiosecossesssesnssassaceseasy

G. The Atmosphere supplied to the Plants ............ A satus

H. The Apparatus used to enclose the Plants, and to coauly ‘hem ait ae Water,
Carbonic acid, GC.) 1....ccccocostsearscadecdcsnesscvredn oud evseesadeseedenessendsespes9

I. Use of the Apparatus .......s.secceccscceeseccescersescsasenseescessescesssoeecssase sssees

J. The supply of Carbonic acid to the Plants .,.........:sccsseccceeececseeccesseceesseees

K. Advantages of the Apparatus adopted ..........ccsscssesescsvcceccnccocceseesecesenesens

L. Adaptation for healthy growth of the conditions of experiment adopted ......

Szorron I1.—Other Conditions of Experiment requiring collateral Investigation :—
BINUMETALION OL cecienisscissicosaeacesscausverscararsasnasdnennoses*assedrareasecdeumtanenesenp
A. General considerations in regard to the possible influence of Ozone on the
supply of combined Nitrogen to growing Plants...........:seeseee0
B. Composition of the Gas in Plants.. So
C. Experiments on the action of Grane air on daenapeeae Greane Malice, ou

porous and alkaline substances) ............42.2-s00+eeeree-coreacasrnescesecsecesesseone
D. Evolution of free Nitrogen in the decomposition of Nitrogenous organic
TIRED ooo 5 opsias san/o's (00's cioniewesle wale oleloacleiwels oe = ain|aic'=isviels.olsineolasn ae Aboard ciabien a anise
E. Experiments on the action of the oxidizing and reducing forces, as manifested
in the decomposition of Nitrogenous orgamicsmatter ......-.. 1.0... seeseeeee eee
F. The mutual relations of Gaseous Nitrogen, and the Nascent Hydrogen evolved
during the decomposition of organic matter...............21.sseseceeeseeeeeceneeeaas

Summary Statement of the Results of the consideration of the conditions required, or involved, in
Experiments on the question of the assimilation of free Nitrogen by Plants .....-...10scseceeoe

Srotton III.—Conditions of growth under which assimilation of Free Nitrogen by Plants is most
likely to take place. Direct Experiments upon the Question under various cir-
cumstances of growth :—

A. General consideration of conditions of growth ~.......ccceccesececee eee ceseee een ceeees
B, Direct experiments on the question of the assimilation of free Nitrogen by plants
I. Experiments in which the plants had no other supply of combined Nitrogen
than that contained in the seed SOW .........s.scsecsseesserececencencercensenees

IL. Experiments in which the plants had a known supply of combined Nitro-
gen, beyond that contained in the original seed ...............-ssseeseeeeeeneees
Relations of the plants grown with an extraneous supply of combined nitrogen,

Od DOSS PTOWA vi NGG St fancrsa-es ccs sec-eane! -«teaen des seanesamcas pedeenceeree sae
WonclUniOnS eee danieanesaseenaseiqasisanase sein docten ae cet een dees aerate delasiasatts saiobaws wee

APPENDIX.

A. Preparation of solutions for manuring the plants, dates of application, and
TIES ADDON a esac css lnn cian cine chs engin ei eee eee researc Pree ease
B. Taking up the plants, preparation for analysis, methods of analysis, &¢
C. Abstract of the Records of Growth of the Plants.
I. Plants grown in 1857 Saath eRe os aeten enneesnebceemsnswacntsen ze

Prares XII. XIII. XIV. and XV.

473—474
474

474—A75
475—476
476—478
478—480
480—481
481—483
483—4584

484

484—456
486—495

495—497

497—508

509—515

515—516

516—517

517—520
520—540

521—529

529—538

538—539
539—540

540—541

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 433

PARE (FLRSE.
GENERAL HISTORY, AND STATEMENT OF THE QUESTION.

Szctioy I—INTRODUCTION, AND EARLY HISTORY.

THE facts at the present time generally accepted regarding the ultimate composition,
and the sources of the constituents, of plants, have, for the most part, received their
preponderating weight of proof within the limits of the present century. But it is to
the century preceding it that we must look for the establishment of much that was
essential as the foundation of those advances which have since been made.

Whatever may be the value at present attached to the particular views of Hates
regarding the composition and the sources of vegetable matter, we must accord to his
labours, in the early part of the eighteenth century, the merit of having been guided by
a proper spirit of experimental inquiry. Nor did he fail in applying to good account,
and even in extending, the then existing knowledge of the material things around him
which were apparently involved in the mysterious processes of vegetable growth.

With our present knowledge, however, of the general composition of plants, and of
the sources of their constituents, it is easy to see how essential was a proper under-
standing of the chemistry of the air, and of water, to any true conceptions of the mate-
rial changes involved in the vegetative process. It can, indeed, hardly excite surprise,
that what may be called the germs of our present knowledge of the chemistry of plant-
growth came forth almost simultaneously with the now adopted views of the compo-
sition of those universal, though not exclusive, media of vegetation—air, and water.

Accordingly, it is between the ‘dates of 1770 and 1800 that we find Biack, ScHEELE,
PriestLey, Lavoister, CAVENDISH, and Warr establishing for us the facts that common
air consists chiefly of nitrogen and oxygen, with a little carbonic acid, that carbonic
acid itself is composed of carbon and oxygen; and that water is composed of hydrogen
and oxygen; and it is within the same period that PriesTtey and In@renHousz, SENNE-
BIER and Woopuotss, laboured to show the mutual relations of these bodies and vege-
table growth.

But the observers last mentioned seem to haye had more prominently in view the
question of the influence of plants upon the media with which they were surrounded,
than that of the influence of these media in contributing materially to the increased
substance of plants themselves. Following closely on their footsteps, both in point of
time and in general plan of research, came Dz Saussure. His labours were conducted
towards the end of the last century and in the beginning of the present one; and their
results, and the arguments he founded upon them, published by him in 1804, may be
said to have indicated, if not indeed established, many of the most important facts with
which we are yet acquainted regarding the sources of the constituents stored up by the
growing plant. To Dr SavssurE we owe the experimental, and even quantitative, illus-
tration of the fact, that plants in sunlight increase in their amounts of carbon, hydro-
gen, and oxygen, at the expense of carbonic acid and of water. It is remarkable, too,
that, in the case of the main experiment he cites on the point, he, with his very imper-

302

434 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

fect methods, found the increase in carbon and in the elements of water to be almost
identically in the proportion in which these are known to exist in the so-denomi-
nated carbo-hydrates. He further maintained the essentialness of the so-distinguished
“mineral” constituents of plants; and he pointed out, in opposition to previous views,
that they were derived from the soil, and were not the result of a creative power exer-
cised by the living plant. He also called attention to the probability that the incom-
bustible or mineral constituents derived by plants from the soil, were the source of those
found in the animals which are fed upon them.

Besides carbon, hydrogen, oxygen, and the more peculiarly mineral constituents, plants
had already been shown to contain nitrogen. Priestley and InGENnovsz thought they
had observed that plants absorbed the free nitrogen of the confined atmospheres in which
they were placed in their experiments. SENNEBIER and WoopHOUSE arrived at an oppo-
site conclusion. De Savssure, again, did not find that plants took up appreciable quan-
tities of the nitrogen supplied to them in the free and gaseous form. On the other
hand, he thought that his experiments indicated rather an evolution of that element at
the expense of the substance of the plant, than any assimilation of it from gaseous
media. On this point he further concluded that the source of the nitrogen of plants
was, more probably, the nitrogenous compounds in the soil, and the small amount of
ammonia which he demonstrated to exist in the atmosphere.

From his results, as a whole, Dr Saussure concluded that air and water contributed
amuch larger proportion of the dry substance of plants, than did the soils in which they
grew. In his view, the fertile soil was the one which yielded liberally to the plant nitro-
genous compounds and the incombustible or mineral constituents; whilst he attributed
to air and water, at least the main part of the carbon, hydrogen, and oxygen of which
the greater portion of the dry substance of the plant was made up.

Up to the present time, carbonic acid and water are admitted to be the chief sources
of the carbon, hydrogen, and oxygen which constitute the great proportion of vegetable
produce. Nor is it questioned that ammonia, and especially ammonia provided within
the soil, is at least an important source of the nitrogen of such produce. But the experi-
ments of De SaussurE—however sagacious his conclusions—were less satisfactory as to
the source of the nitrogen, than as to that of the carbon, hydrogen, and oxygen, of vege-
table matter.

It will not be supposed, from what has just been said, that there remain no questions,
of vast scientific as well as of practical interest, to be yet solved, regarding the con-
ditions under which our different crops take up their carbon, hydrogen, and oxygen. At
the same time, those who devote themselves to the subject of Agricultural Chemistry
soon find that the explanation of the chemical phenomena of agricultural production
awaits much more for a further elucidation of the sources, and of the modes of assimila-
tion, of the nitrogen than of the other, so-called, organic elements of our crops—carbon,
hydrogen, and oxygen.

In 1837, BoussineavLt took up the subject of the sources of the Nitrogen of plants,
where Dr SavussurE had left it more than thirty years before. To the investigations

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 435

and conclusions of BoussINGAULT, and others, in connexion with this question, from the
date above mentioned up to the present time, we shall have to refer pretty fully further
on. It may here be mentioned, however, that already at that early period Bovs-
SINGAULT had so far advanced in his inquiries into the chemical statistics of certain agri-
cultural practices on the large scale, as to be apparently led by them to see the import-
ance of investigating much more closely the sources of the Nitrogen periodically yielded
by a given area of land, over and aboye that which was artificially supplied to it.

We fully admit the pertinence of the considerations, and the sagacity of the observa-
tions adduced on this head, more than twenty years ago, by Boussineauur. It will,
nevertheless, be well to preface the discussion of our own experimental evidence regard-
ing the sources of the nitrogen of plants, by the statement of a few prominent and
striking facts, established by investigations conducted here, at Rothamsted, illustrative
of the amounts of nitrogen yielded by different crops over a given area of land, and of
the relation of these amounts to certain measured, or known, sources of it. Of these
points, however, we profess to speak only in a very brief and summary manner on the
present occasion. The discussion in detail, of the evidence relating to them, would
indeed itself exhaust the limits of our Paper. Moreover, we have already treated of
this subject in a separate form, elsewhere *; and it is our intention to consider it much
more fully at some future opportunity.

Section I.—ANNUAL YIELD OF NITROGEN PER ACRE, IN DIFFERENT CROPS.
A.— Yield of Nitrogen per acre when the same Crop is grown year after year
on the same Land.
The following Summary Table shows the average annual amounts of nitrogen yielded

per acre, in the crops enumerated, when each was grown for a number of years con-
secutively on the same land, without manure.

TABLE I,
- Average Annual yield of
Description of Crop. Dates of ae Experi- Number of Years. Nicogen per ae
HANS without Manure.
Wikheatiresccsccosecsees 1844—1859 inclusive 16
Barley ......se+0+4+«/1852—1859 inclusive 8
Meadow Hay... sess 1856-—1 859 inclusive
Beans ......e0eeeeeeeee4/1847—] 858 inclusive 12

There were obtained, then, in each of the Cereal crops (wheat and barley) about
243 lbs. of Nitrogen per acre, per annum, without manure. In the case of each of the
crops the land was, in an agricultural sense, exhausted at the commencement of the

* British Association for the Advancement of Science, Leeds Meeting (1858), Section B.

+ The results given in this Section have been revised, and in some cases the periods over which the
estimates are taken extended, since the reading of the Paper.

436 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

experiment; that is to say, it had been brought to such a condition by previous crop-
ping, that, in the ordinary course of practice, it would be deemed necessary to supply
manure to it before growing another corn-crop. It may be further remarked that in
the case of the wheat there is as yet little, but in that of the barley more obvious
indication of progressive decline in the annual yield.

The meadow-land yielded nearly 40 lbs. of Nitrogen per acre, per annum, or above
one-half more than the exclusively Graminaceous crops, wheat and barley. ‘The hetero-
gencous produce, meadow-hay, contained, however, a good deal of Trifolium, and other
Leguminous plants, intermixed with the Grasses. To this fact is to be attributed, at
least in great part, its comparatively high amount of Nitrogen. It should be observed,
too, that the average is as yet taken over only four years.

The Leguminous crop (beans) has given, over a period of twelve years, an average of
nearly 48 lbs. of Nitrogen per acre, per annum. ‘The yield of Nitrogen in this Legumi-
nous crop was, therefore, nearly twice as great as in the Graminaceous corn-crops. The
bean and allied crops are, however, very subject to disease, especially when grown too
frequently on the same land. It is, at least in part, owing to this circumstance, that
the average annual yield over the twelve years was so much less than would be the
yield of the crop when grown in suitable alternation with others in a season of average
adaptation for its healthy development. In fact, so great was the deterioration in the
character and amount of produce in the experiments in question, due to the continuous
cropping, that whilst the average annual yield of Nitrogen over the first six of the
twelve years was 70 lbs., that over the concluding six years was only 26 lbs. Nor did
the addition of nitrogenous manure in the form of ammonia-salts, together with liberal
mineral manuring, obviate this deterioration in any material degree more than did
mineral manures alone.

In further illustration of the larger amount of Nitrogen obtained over a given area of
land in Leguminous crops than in Graminaceous ones, some remarkable results with
clover may be cited. Red clover was grown in three out of four consecutive years, the
intermediate crop being wheat—all without manure. The following amounts of
Nitrogen were obtained per acre :—

TaBeE II.

Season. Crop. Nitrogen per acre. |
Ibs.
Ist Year, 1849 ...... 206°8
(2nd Year, 1850 .. 45:2)
3rd Year, 1851...... 29°3

4th Year, 1852...... 111-9

Bee eeeeee

All further attempts to grow clover year after year, on this land, have, however,
failed. Neither ammonia-salts, nor organic matter rich in carbon as well as other
constituents, nor mineral manures, nor a mixture of all has availed to restore the

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 437

clover-yielding capabilities of the land. On the other hand, it should be particularly
observed that, after taking 206-8 lbs. of Nitrogen from an acre of land in the clover-
crop of the first year, the wheat-crop of the second or succeeding year, compared with
that of the same season in the adjoining experimental wheat-field where the crop is
grown year after year on the same land, was about double that obtained from the plot
which had there been unmanured for a series of consecutive years, and fully equal to that
from a plot which had for the same period received annually a dressing of farm-yard
manure. It should be added that, after failing to get any crop of clover at all in 1853
and in 1854, and getting a very poor one in 1855, the land was allowed to lie fallow
for two years; that after this, in 1858, there was obtained an over-luxuriant and laid
crop of barley, more than twice as great as the average annual produce of eight years
of the successive growth of the crop without manure in the same field; yet, after
resowing with clover in the spring of 1859, and getting a small cutting in the autumn
of the same year, the plant has again died off during the winter of 1859-60. This was
the case notwithstanding that it was a perennial variety that was last sown.

Again, eight consecutive crops of turnips (four “ White Globe” and four ‘‘ Swedish”)
gave an average annual yield, per acre, of about 40 lbs. of Nitrogen, without the supply
of any inthe manure. In the case of these turnips, however, the land received annually
certain “mineral” manures. In fact, turnips grown year after year without manure of
any kind, yielded, after a few years, only a few hundred-weights of produce per acre;
but the percentage of Nitrogen in these diminutive unmanured turnips was very un-
usually high. It will be observed that the average annual yield of Nitrogen per acre,
in the turnips grown by mineral manures (containing no Nitrogen), was considerably
more than that in the unmanured Cereal grain-crops. And, in connexion with this
point, it is worthy of remark, that, on barley, without manure, succeeding on the land
from which these eight mineral-manured turnip-crops had been taken, the produce
was only about three-fourths as much as that obtained, in the same season, where
barley was grown for the second year in succession without manure, in another field ;
and it was only about three-fifths as much as that obtained, also in the same season,
where barley was grown as the second crop of the second course, in a series of entirely
unmanured four-course Rotation-crops.

It may be mentioned that, in the case of the purely Graminaceous crops, there has
been but very little gain in the annual yield of Nitrogen per acre by the use of mineral
or non-nitrogenous manures. But in the case of the Leguminous crops, as in that of the
root-crops just referred to, there has been much more Nitrogen harvested over a given
area, within a given time, when mineral manures were employed, than when no manure
at all was used.

It has thus far been seen, then, that the Leguminous crops yield much more Nitrogen
over a given area than the Graminaceous ones, and, further, that the amount of Nitro-
gen harvested in the former is increased considerably by the use of “ mineral” manures,
whilst that in the latter is so in a very limited degree. It is, nevertheless, a well-known
agricultural fact, that the growth of the Leguminous crops, which carry off such a com-

438 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

paratively large amount of Nitrogen, is one of the best preparations for the after-growth
of wheat. On the other hand, it is equally true that fa//ow—one important effect of
which is to accumulate within the soil the available Nitrogen of two or mere years for
the growth of one—and adding nitrogenous manures, have each much the same effect in
increasing the produce of the Cereal crops.

B.—Yield of Nitrogen per acre when Wheat is grown in alternation with
Beans, or with Fallow.

The striking and interesting fact, that the growth (and removal from the land) of a
highly nitrogenized Leguminous crop, and fallow, have each the effect of increasing the
amount of produce, and with it the yield of Nitrogen per acre, of a succeeding Cereal
crop, is briefly illustrated by the summary of direct experimental results given in the
following Table :—

TaBLe ITI.

Showing the Amount of Nitrogen obtained per acre, in Wheat grown consecutively, in
Wheat alternated with Beans, and in Wheat alternated with Fallow.

Period of Experiment ten years, 1850—1859 inclusive.

Nitrogen per acre, lbs.

Total. | Average annual.
WE hori uae gritty one's. CE anheg rae |

Beans —10 erops consecutively { WinO\r MANNE wrseterrenee| 8 Tod
Wheat—without Manure {73 Grohs citernated with Fallow ccc] 2193 | 439 of 2149 |
Se re ee ee ee eer itl ceite lan eed
Bence parte Mineral Manure 4 2 Gee vaste eee hea a eee VE eae

It is seen, then, that ten consecutive crops of beans, without manure of any kind,
gave an average annual yield of Nitrogen, per acre, of 34:7 lbs.; and ten consecutive
crops with “mineral” but without nitrogenous manure gave an average annual yield,
per acre, of 51:1 Ibs.

During the same period, ten consecutive crops of wheat without manure of any
kind gave annually 23-4 lbs. of Nitrogen, or less than half as much as the beans
with mineral but without nitrogenous manure. Again, extending over the same
series of years, five crops of wheat alternated with fallow gave, taking the average of
the five years under crop, 43-9 Ibs., and on the average of the ten years, 21:9 lbs. per
acre, per annum, of Nitrogen., That is to say, the wheat alternated with fallow gave,
taking the average of the five years of its growth, nearly twice as much Nitrogen
annually as the wheat grown after wheat in the same seasons. The total Nitrogen
cbtained, per acre, over the ten years, was, however, pretty much the same in the two

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 439

cases,—namely, 234 Ibs. in the ten crops of wheat grown consecutively, and 219-3 3 Ibs.
in the five crops of wheat alternated with fallow.

Again, five crops of wheat alternated with beans gave 45:2 Ibs. of Nitrogen per acre,
per annum, over the five years—equal half that amount, or 22-6 lbs., averaged over the
ten years. The total amount of Nitrogen obtained during the ten years was, in the
ten crops of wheat grown consecutively, 234 Ibs., in the five crops of wheat alternated
with fallow, 219-3 lbs., and in the five crops of wheat alternated with beans, 225°8 lbs.
—or not very materially different in the three cases. But, notwithstanding that the
land has thus yielded in wheat, over ten years, almost as much total Nitrogen in five
crops alternated with beans, as in ten crops grown consecutively, and rather more than in
five crops alternated with fallow, the five intermediate crops of beans have, in addition
to this, themselves carried off more than the same amount of Nitrogen as the wheat—
namely, 244°5 lbs.

The general result is, then, that pretty nearly the same amount of Nitrogen was taken
from a given area of land in wheat, in ten years, whether ten crops were grown con-
secutively, five crops in alternation with fallow, or five crops in alternation with beans.
In fact, the crop of wheat was increased fully as much when it succeeded Jeans, which
carried off a large amount of Nitrogen, and of mineral matters also, as when it succeeded
fallow, which conserved the stores both of Nitrogen and of mineral matter.

It will be seen, by the illustrations given in the next sub-section (C.), that the experi-
mental results thus far adduced are perfectly consistent in character with those obtained
under circumstances more nearly allied to those of ordinary farm practice.

C.— Yield of Nitrogen per acre when crops are grown in an actual course of rotation.

In BoussinGAvutt’s experiments, he obtained, taking the results of six separate courses
of rotation, an average of between one-third and one-half more Nitrogen in the produce
than had been supplied in the manure. He found, moreover, that the largest yields of
Nitrogen were in the Leguminous crops, and, further, that the Cereal crops were the
larger when they next succeeded upon the removal of the highly nitrogenized Legumi-
nous crops.

For our own experiments at Rothamsted upon an actual course of rotation, a piece
of land was selected which was, in an agricultural sense, exhausted; that is to say, it
had grown a course of crops since the application of manure, and would, under ordinary

= e ay ™ fig) G3 fn

438 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

paratively large amount of Nitrogen, is one of the best preparations for the after-growth
of wheat. On the other hand, it is equally true that fa//ow—one important effect of
which is to accumulate within the soil the available Nitrogen of two or mere years for
the growth of one—and adding nitrogenous manures, have each much the same effect in
increasing the produce of the Cereal crops.

B.—Vield of Nitrogen per acre when Wheat is grown in alternation with
Beans, or with Fallow.

The striking and interesting fact, that the growth (and removal from the land) of a
highly nitrogenized Leguminous crop, and fallow, have each the effect of increasing the
amount of produce, and with it the yield of Nitrogen per acre, of a succeeding Cereal
crop, is briefly illustrated by the summary of direct experimental results given in the
following Table :—

TaBLeE III.

Showing the Amount of Nitrogen obtained per acre, in Wheat grown consecutively, in
Wheat alternated with Beans, and in Wheat alternated with Fallow.

Period of Experiment ten years, 1850—1859 inclusive.

|
Nitrogen per acre, lbs.

Total. | Average annual.
2 , wd Nu thoute Man irese—..ncrmecs--b sebmeeessee 346°9 34°7

Beans——10 crops consecutively ee Mineral Manure ....secssssseses-| 510° B11 |
é - 10 Crops consecutively.............0+0+2| 234°0 23-4
Wheat—without Manure { 5 Crops alternated with Fallow...... 219°3 | 43-9 of 21°9 |
|
Wheat] _- 5 Crops alternated with Beans ...... 225°8 | 45:2 or 22:6 |
Beans } without Manure { 5 Crops alternated with Wheat...... 2445 | 48°9 or 24°5

Wheat] _. 4 ~ 5 Crops alternated with Beans ...... 207°0 | 41-4 or 20°7
Beans \ with Mineral Manure { 5 Crops alternated with Wheat...... 227-2 | 45°4 or 22-7 |

It is seen, then, that ten consecutive crops of beans, without manure of any kind,
gave an average annual yield of Nitrogen, per acre, of 34:7 Ibs.; and ten consecutive
crops with “mineral” but without nitrogenous manure gave an average annual yield,

per acre, of 51-1 Ibs.

Note—At page 439, line 3 from bottom, after “.
average annual amount, per acre, of 42:6 lbs.” insert
The second and third courses gave, however, much less
than the first, and hence a less average per annum

than that stated for the twelve years.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 459

cases,—namely, 254 Ibs. in the ten crops of wheat grown consecutively, and 219-3 Ibs,
in the five crops of wheat alternated with fallow.

Again, five crops of wheat alternated with beans gave 45:2 lbs. of Nitrogen per acre,
per annum, over the five years—equal half that amount, or 22°6 Ibs., averaged over the
ten years. The total amount of Nitrogen obtained during the ten years was, in the
ten crops of wheat grown consecutively, 254 lbs., in the fe crops of wheat alternated
with fallow, 219-3 lbs., and in the five crops of wheat alternated with beans, 225°8 lbs.
—or not very materially different in the three cases. But, notwithstanding that the
land has thus yielded in wheat, over ten years, almost as much total Nitrogen in five
crops alternated with beans, as in ten crops grown consecutively, and rather more than in
five crops alternated with fallow, the five intermediate crops of beans have, in addition
to this, themselves carried off more than the same amount of Nitrogen as the wheat—
namely, 244°5 lbs.

The general result is, then, that pretty nearly the same amount of Nitrogen was taken
from a given area of land in wheat, in ten years, whether ten crops were grown con-
secutively, five crops in alternation with fallow, or five crops in alternation with beans.
In fact, the crop of wheat was increased fully as much when it succeeded beans, which
carried off a large amount of Nitrogen, and of mineral matters also, as when it succeeded
fallow, which conserved the stores both of Nitrogen and of mineral matter.

It will be seen, by the illustrations given in the next sub-section (C.), that the experi-
mental results thus far adduced are perfectly consistent in character with those obtained
under circumstances more neatly allied to those of ordinary farm practice.

C.— Yield of Nitrogen per acre when crops are grown in an actual course of rotation.

In BousstnGavtt’s experiments, he obtained, taking the results of six separate courses
of rotation, an average of between one-third and one-half more Nitrogen in the produce
than had been supplied in the manure. He found, moreover, that the largest yields of
Nitrogen were in the Leguminous crops, and, further, that the Cereal crops were the
larger when they next succeeded upon the removal of the highly nitrogenized Legumi-
nous crops.

For our own experiments at Rothamsted upon an actual course of rotation, a piece
of land was selected which was, in an agricultural sense, exhausted; that is to say, it
had grown a course of crops since the application of manure, and would, under ordinary
practice, have received a new supply before growing another crop. On this land the
four-course rotation of Turnips, Barley, Leguminous crop (or Fallow), and Wheat, in
the order of succession here enumerated, and without manure, has now been followed
for twelve years—that is, through three separate courses. The yield of Nitrogen during
these twelve years, or three courses, has been determined; and the result shows an
average annual amount, per acre, of 42:6 lbs. This, it will be remembered, is nearly
twice as much as was obtained in either wheat or barley when these crops were, respect-
ively, grown year after year on the same land. The greatest yield of Nitrogen obtained

MDCCCLXI. 3P

440 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

in the Rotation experiment was in the case of a clover-crop, grown once during the
twelve years, and which constituted the Leguminous crop of the first course. After both
this clover-crop (in which was removed such a large amount of Nitrogen) and beans which
replaced it in the second and third courses (but which gave a very small yield of Nitrogen),
the wheat-crop was about double as much as the average where wheat has been grown
succeeding wheat, and it was about equal to the average per crop when wheat was
grown after fallow, or after beans, in the experiments already referred to.

It has been seen, then:—that even Cereal crops grown, year after year, on the same
land, gave an average of about 24} 1bs. of Nitrogen per acre, per annum; that, under
similar circumstances, Leguminous crops gave much more; that, nevertheless, the pro-
duce of the Cereal crop was nearly doubled when it was preceded by the more highly
nitrogenized Leguminous crop; that the produce of the Cereal crop was also nearly
doubled when it was preceded by fallow; and lastly, that in an actual rotation of crops,
though entirely without manure, there was also an average annual yield of Nitrogen
nearly twice as great as that obtained in the continuously grown Cereal.

It has been incidentally mentioned, too, that the highly nitrogenous Leguminous crops
are comparatively little benefited by the direct application of nitrogenous manures (am-
monia-salts). It has also further been stated, on the other hand, that, notwithstanding
the comparatively small amount of Nitrogen harvested in a Cereal crop, and that both
the crop and its Nitrogen are very much increased when succeeding upon the growth
and removal of a highly nitrogenous Leguminous crop, yet the application of nitroge-
nous manures is also one of the surest means of increasing the produce, and the yield of
Nitrogen, of a Cereal crop.

D.—Relation of the increased yield of Nitrogen in the produce, to the amount
supplied, when nitrogenous manures are employed.

Not only do we harvest in our crops (particularly the Leguminous ones) a large
amount of Nitrogen, the source of which, it will afterwards be seen, is by no means fully
explained, but, when we increase their growth (particularly that of the Cereals) by the
direct application of nitrogenous manures, it is found that, over a series of years, a con-
siderable proportion of the so-supplied Nitrogen is not recovered in the increase of crop.

Thus, when a certain amount of ammonia-salts (in addition to a complex mineral
manure) was applied, year after year, for the growth of wheat, the result, taken over a
period of six years, was, that the increased yield of Nitrogen in the crop was only equal
to about 43 per cent. of the Nitrogen which had been supplied in the manure. When
double the amount of ammonia-salts was employed, by which the crop was still further
increased, the proportion of the supplied Nitrogen which was recovered as increase was
almost identically the same; but with more still, the proportion was less.

Again, when the smaller amount of ammonia-salts was applied annually, for six years,
to barley, the increased yield of Nitrogen corresponded to only about 42 per cent. of the

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 44]

Nitrogen supplied in the manure; and when the double amount of the manure was
employed for barley, over the same series of years, only about 43 per cent. of the sup-
plied Nitrogen were recovered as increased yield.

To the statement of these facts it should be added that the Nitrogen (equal in amount
to, say 60 per cent. of that supplied in the manure) which is not obtained as increased
yield in the immediate crop does not appear to exist in the soil availably for an imme-
diately succeeding crop. ‘Thus, when by the use of nitrogenous manures an increased
yield of Nitrogen has been obtained in the first succeeding wheat-crop, equal in amount
to about 40 per cent. of the Nitrogen supplied in the manure, the increased yield obtained
in the second crop, without any further supply, is equal to little more than one-tenth of
the remainder.

In connexion with this subject it may be mentioned that, so far as our experiments with
meadow-qrasses at present show, it does not appear that the increased yield of Nitrogen
in the crop on the use of nitrogenous manures bears a much higher proportion to the
amount supplied in their case than in that of either wheat or barley. In the case of
the Leguminous corn-crops, the proportion of the increased yield to the amount supplied
appears to be even less than in that of the Cereal grains. Root-crops, on the other hand,
would seem to gather up an increase of Nitrogen bearing a larger proportion to the
quantity directly supplied in the manure.

On the assumption that the relation of the immediately increased yield of Nitrogen
to the amount supplied in manure represents really or approximately the proportion of
the directly supplied Nitrogen which is actually recovered in the immediate crop, the
following questions seem to suggest themselves :—

Is the unrecovered amount of supplied Nitrogen, or at any rate a considerable pro-
portion of it, drained away and lost?

Are the nitrogenous compounds transformed within the soil, and their Nitrogen, in
some form, evaporated ?

Does the missing amount for the most part remain in some fixed combination in the
soil, only to be yielded up, if ever, in the course of a long series of years ?

Is ammonia itself, or Nitrogen in the free state, or in some other form of combination
than ammonia, given off from the surface of the growing plant? Or, lastly,

When Nitrogen is supplied within the soil for the increased growth of the Grami-
naceous crop, is there simply an unfavourable distribution of it, considered in relation
to the distribution of the underground feeders of the crop?—the Leguminous crop,
which alternates with it, gathering from a more extended range of soil, and leaving a
residue of assimilable Nitrogen within the range of collection of a next succeeding
Cereal one?

But other and wider questions than those just enumerated present themselves on a
careful review, as a whole, of the Nitrogen-statistics of field-produce to which attention
has briefly been directed. For the moment, all may be asked in one—namely, What

3P2

442 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

are the sources of all the Nitrogen of our crops beyond that which is directly supplied
to the soil by artificial means? This brings us to a consideration of the next Section
of our subject.

Srorron II]L—GENERAL VIEW OF THE VARIOUS ACTUAL OR POSSIBLE SOURCES
OF THE NITROGEN OF OUR CROPS.
The following actual or possible sources of the Nitrogen obtained in our crops, beyond
that supplied in manure, may be enumerated :—
1. The Nitrogen in certain constituent minerals of the soil, especially the ferruginous
and aluminous; and certain nitrides.
2. The combined Nitrogen annually coming down in the aqueous depositions from the
atmosphere :—
(a) As ammonia.
(4) As nitric acid.
(c) As organic corpuscles, &c.
3. The accumulation by the soil of combined Nitrogen from the atmosphere :—
(a) By surface absorption aided by moisture.
(2) By the chemical action of certain mineral constituents of the soil.
(ce) By the chemical action of certain organic compounds in the soil.

4. The formation of ammonia in the soil, from free Nitrogen, and nascent Hydrogen
(the so-formed ammonia either remaining as such, or being oxidated into nitric acid).

d. The formation of nitric acid from free Nitrogen :—

(a) By electric action.
(4) With common Oxygen, in contact with porous and alkaline substances.
(c) Under the influence of Ozone, or nascent Oxygen.

6. The direct absorption of combined Nitrogen from the atmosphere, by plants them-
selves.

7. The assimilation of free Nitrogen by plants.

A careful consideration of the above actual or possible sources of the Nitrogen of the
vegetation which covers the earth’s surface will show, in regard to some of them, that
they at least are quantitatively inadequate to supply the amounts of Nitrogen which
direct experiment has shown to be removable in various crops from a given area of land.

(1) The combined Nitrogen that may be due to certain of the constituent minerals of
the débris of which our soils are made up cannot be supposed to be an adequate source
of the nitrogen annually carried off in the vegetable produce of the land.

(2) The combined Nitrogen which comes down from the atmosphere in the various
aqueous deposits of rain, hail, snow, mists, fog, and dew—whether it be merely the
return from previously existing generations of plants or animals elsewhere, or whether
in part the product of a new formation—undoubtedly does contribute materially to the

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC, 443

annual yield of Nitrogen in our crops. The amount of Nitrogen derivable from these
sources is, moreover, perhaps more readily quantitatively estimated than that from any
of the other sources enumerated. Accordingly, much labour has, of late years, been
bestowed in determining the amounts of ammonia and nitric acid in these several aqueous
deposits. Extensive series of observations have been made on these points by Boussin-
GAULT, BARRAL, Way, and two of ourselves; and others have experimented on a more
limited scale. It may be stated, generally, that the rain of the open country has indi-
cated an average of very nearly the same amounts of ammonia in the hands of Boussin-
GAULT in Alsace, and of Way and ourselves in England. The most numerous and reliable
determinations of the amount of nitric acid in rain-water are probably those of Mr. Way.

By the aid of numerous determinations of the ammonia by ourselves, and of both the
ammonia and nitric acid by Mr. Way, we are enabled to form an estimate of the total
amount of Nitrogen coming down as ammonia and nitric acid in the total rain, hail,
and snow, and in some of the minor aqueous deposits, during the years 1853, 1856,
and 1856, here at Rothamsted, where the experiments relating to the acreage yield of
Nitrogen in the different crops were made. The result was, that in neither of the three
years did the Nitrogen so coming down as ammonia and nitric acid amount to 10 lbs.
per acre.

Supposing the combined Nitrogen coming down in the direct aqueous deposits were
to be estimated, in round numbers, at 10 lbs. per acre, per annum, this amount would
supply less than half as much Nitrogen as was annually removed in the continuously
grown wheat and barley crops. It would amount to only about one-fourth of that
which was obtained in the hay, and in the turnips; to a less proportion of that obtained
in beans; and to a still less proportion of that obtained in the clover. Lastly, it would
amount to only about one-fourth as much as was obtained per annum, over twelve years
of ordinary Rotation, but without manure of any kind either during that period or for
some years previously.

We are driven, then, to seek for other sources of the Nitrogen of our crops, than
that which comes down as ammonia and nitric acid in the more direct and more easily
measurable aqueous deposits from the atmosphere. Nor does it appear, so far as can
be judged from the results of BousstNGAULT on this point, that the amounts of combined
Nitrogen deposited by dew are such as to lead to the supposition that our approximate
estimate would require any material modification, were as large a proportion of dew
included in our collected and analysed aqueous deposits as is probably received by the
soil itself or the vegetation which may cover it.

(3) With regard to the amounts of combined Nitrogen accumulated by the soil from
the atmosphere by virtue of surface absorption, or chemical action, it is, probable that
they constitute no inconsiderable proportion of that which is annually available for
vegetation over a given area of land. Numerous investigations have indeed been under-
taken during the last few years, both by ourselves and others, to determine the actual or
relative capacities for absorption of different soils, or constituents of soils. Unfortu-

444 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

nately, however, even quantitative results established by laboratory methods do not
admit of very direct and certain application in accounting, quantitatively, for the amount
of combined nitrogen that may be so fixed, to a given depth, over a given area of land,
within a given time. We hope, however, to treat of this subject in some detail on some
future occasion.

(4 & 5) The circumstances of the formation of ammonia, or nitric acid, from gaseous,
dissolved, or nascent Nitrogen, are at present involved in too much obscurity, and are
the subject of too much conflicting statement for their consideration to serve us much
in our present inquiry. The various assumed actions are, as yet, by no means all
clearly established in a merely qualitative way; and still less, quantitatively. More-
over, as in the case of absorption, so in that of the formation of ammonia, or of nitric
acid, there would be considerable difficulty and uncertainty in applying the results
of laboratory experiments to the estimation of the probable amount of the Nitrogen
of vegetation due to such sources. ‘To some of the questions involved, we shall, how-
ever, have to refer more or less in detail in discussing the conditions of the experiments
which will form the subject of the second part of the present Paper.

(6) With regard to the direct absorption of ammonia or nitric acid from the air by
plants themselves, we have little of either qualitative or quantitative evidence of any
kind to guide us. Still, a few observations may be usefully hazarded, in passing, which
may bear more or less directly upon the point.

In our ripened Cereal crops, we find 1 part of Nitrogen to somewhere about 30 parts
‘of carbon; and in our Leguminous crops, 1 part of Nitrogen to about 15 or fewer parts
of carbon. It is supposed that the atmosphere, on the average, contains 1 part (or
rather more) of carbon in the form of carbonic acid to 10,000 parts of air. We may
perhaps assume, as an extreme amount, that the atmosphere contains only 1 part of
Nitrogen in the form of ammonia to about 12,000,000 parts of air. Adopting these
assumptions, there would obviously be, instead of only 30 or 15 times less Nitrogen
than carbon (as in the respective crops), 1200 times less Nitrogen in the ambient air in
the form of ammonia, than of carbon in the form of carbonic acid in the same medium.

If, however, we were to adopt as more nearly the amount of ammonia in the air that
found by M. G. VILLE (namely, only about one-fifth as much as we have assumed above),
it would then appear that there were 6000 times less of Nitrogen in the air in the form
of ammonia, than of carbon in that of carbonic acid.

Taking the former or more favourable assumption of the two, the result would be,
that the ambient atmosphere contained Nitrogen as ammonia, to carbon as carbonic
acid, in a proportion 40 times less than that of Nitrogen to carbon in the Cereal pro-
duce, and 80 times (or more) less than that of Nitrogen to carbon in the Leguminous
produce. Adopting M. G. VituE’s estimates, on the other hand, the proportion of the
so-combined Nitrogen to the so-combined carbon, in the air, would be 200 times less
than that of the Nitrogen to the carbon in the Cereal crops, and about 400 times less
than that of the Nitrogen to the carbon in the Leguminous crops.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 445

Looking, therefore, at the subject from the point of view of actual quantity merely,
the ammonia in the atmosphere would appear very inadequate to yield Nitrogen in a
degree at all corresponding to the yield of carbon by carbonic acid. It would appear
too, from the observations hitherto recorded bearing upon the point, that the amount of
Nitrogen existing in the atmosphere as nitric acid is very much less than that existing
as ammonia. Hence, the inclusion, in the estimate of the combined Nitrogen in the
atmosphere, of the amount existing as nitric acid would, in point of quantity, by no
means materially affect the question.

But it is worthy of remark, in reference to the question of the proportion of Nitrogen
as ammonia to carbon as carbonic acid, that may be available to vegetation from
atmospheric sources, that, although the actual amount of Nitrogen as ammonia in the
atmosphere is very small compared with that of the carbon as carbonic acid, yet, a
given amount of water would absorb very much more Nitrogen as ammonia, or dissolve
very much more Nitrogen as carbonate of ammonia, than it would absorb of carbon
in the form of carbonic acid under equal circumstances. In illustration, it may be
mentioned that water at 60° F. (about 15°5 C.) would at the normal pressure absorb
about 850 times as much Nitrogen in the form of ammonia as it would of carbon in
the form of carbonic acid; and, under equal circumstances, very many times more
Nitrogen as carbonate or even as bicarbonate of ammonia would be dissolved, than
there would be of carbon as carbonic acid absorbed. There would appear to be, then,
a compensating quality for the small actual amount of Nitrogen as ammonia in propor-
tion to carbon as carbonic acid in the atmosphere, in the greater absorbability or solu-
bility of the compounds in which Nitrogen exists than of the carbonic acid in which
the carbon is presented. How far, however, the compensating quality here suggested
may really influence the proportion of the Nitrogen to the carbon ayailable from the
atmosphere, in the combined form, under the actual conditions involved in vegetation, is
a question the numerous and intricate bearings of which we do not profess here to
enter upon.

Before passing from this question of the direct absorption of Nitrogen in the com-
bined form from the atmosphere by plants themselves, one or two further observations
may yet be made which are suggested by the actual facts of agricultural production.
It is undoubtedly the case that the Graminaceous crops depend yery materially upon
combined Nitrogen within the soil, to determine the amount of their produce. They
seem, however, to be comparatively independent of carbonic acid yielded by manure
within the soil. The Leguminous crops, on the other hand, appear to be much less
benefited by direct supplies of characteristically nitrogenous manures. It would hence
seem that they are more able to avail themselves of Nitrogen supplied in some way by
the atmosphere, possibly by the aid of their green parts. But it can hardly be toa
greater mere extent of surface above ground that the property which the Leguminous
plants possess of acquiring a greater amount of Nitrogen than the Graminaceous ones,
over a given area of land, and under otherwise equal circumstances, is to be attributed.

446 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

A bean and a wheat crop may yield equal amounts of dry matter per acre, whilst the bean
produce would contain from two to three times as much Nitrogen as the wheat. Never-
theless some attempts at approximate measurement have indicated that the wheat-plant
offers a greater external superficies in relation to a given weight of dry substance, than
does the bean. The wheat-plant would, of course, show a still higher relation of super-
ficies to a given amount of Nitrogen fixed. If, therefore, the larger amount of Nitro-
gen yielded per acre by a bean than by a wheat crop be due to a larger assumption of
it directly from atmospheric sources in some form, it is obvious that the result must be
due to character, and function, and not to mere extent of surface above ground. In
connexion with this point it may be observed, more particularly with reference to the
crops that are grown for their ripened seed, that the Leguminous ones generally main-
tain their green and succulent surface in relation to a more extended period of the
season of active growth and accumulation than do the Graminaceous ones.

(7) Assimilation of free or uncombined Nitrogen by Plants.—It has been seen, in the
course of the foregoing brief review of the various sources of combined Nitrogen to
plants, that those of them which have as yet been quantitatively estimated are inade-
quate to account for the amounts of Nitrogen obtained in the annual produce of a given
area of land beyond that which may be attributable to the supplies by previous manuring.
It must be admitted, too, that the sources of combined Nitrogen which have been alluded
to as not yet even approximately estimated in a quantitative sense (if indeed they are all
fully established qualitatively) offer many practical difficulties in the way of any such
investigation of them as would afford results directly applicable to our present purpose.
It appeared, therefore, that it would be desirable to settle the question, whether or
not that vast storehouse of Nitrogen, the atmosphere, in which the vegetation which
covers the Earth’s surface is seen to live and flourish, be of any measurable ayail to the
growing plant, so far as its free or uncombined Nitrogen is concerned.

The settlement of this question (whether affirmatively or negatively) would at any
rate indicate the degree of importance to be attached to the remaining open points of
inquiry. Indeed, were it found that plants generally, or some of those we cultivate
more than others, were able to fix Nitrogen from that presented to them in the free or
uncombined form, we should, in this fact, have a clue to the explanation of much that
is yet clouded in obscurity in connexion with the chemical phenomena of Agricultural
production. We should establish for vegetation, the attribute of effecting chemical
combinations with an element at once the most reluctant to associate itself with other
bodies in obedience to laboratory processes and at the same time apt to rid itself of
connexions once formed in the most violent manner—as the explosive character of many
Nitrogen compounds forcibly illustrates. We should further be able, much more satis-
factorily than we are at present, to account—by processes established to be going on
under our own observation—for the actually large total amount of combined Nitrogen
which we know to exist and to circulate, in land and water, in animal and vegetable
life, and in the atmosphere.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 447

But another and potent reason for investigating the relation of plants to the free or
uncombined Nitrogen of the atmosphere is to be found in the fact, that the question
has, of late years, been submitted to an immense amount of research by numerous
experimenters, and from the results obtained very opposite conclusions have been
arrived at. Thus, M. Boussrycautr concludes that plants do not assimilate the free
or uncombined Nitrogen of the atmosphere. M. G. VILLE maintains, on the contrary,
that the assimilation of free Nitrogen does take place, and further, that, under favour-
able circumstances, a considerable proportion of the Nitrogen of a plant may be derived
from this source. Others have experimented in connexion with the subject on a more
limited scale; and various explanations have been offered of the discrepant results and
conclusions of M. BoussinGauLt and M. G. VILLE.

Before entering upon the discussion of our own experimental evidence in regard to
the question of the assimilation of free or uncombined Nitrogen by plants, it will be
desirable to pass in review the methods, results, and conclusions of M. BoussrnGauLt
and M. G. Vite, and also of some other experimenters, who seem to have been led to
take up the subject by a consideration of the contrary opinions arrived at by BoussinGauLt
and VILLE.

Section IV.—REVIEW OF THE RESEARCHES OF OTHERS, ON THE QUESTION OF THE
ASSIMILATION OF FREE NITROGEN BY PLANTS, AND ON SOME ALLIED POINTS.

It has already been mentioned that, in 1837, Bousstn@aur took up the question of
the sources of the Nitrogen of Plants where De Saussure had left it more than thirty
years before. Dr Saussure and his predecessors had sought to solve the question, among
others, whether plants assimilated the free or uncombined Nitrogen of the atmosphere,
by determining the changes undergone in the composition of limited volumes of air by
the vegetation of plants within them. BovussinGavir pointed out that the methods
which had been adopted were not sufficiently accurate for the determination of the point
in question. The general plan instituted by himself, and adopted with more or less
modification in most subsequent researches, was :—

To set seeds or plants, the amount of Nitrogen in which was estimated by the analysis

of carefully chosen similar specimens.

To employ soils and water containing either no combined Nitrogen, or only known
quantities of it.

To allow the access, either of free air (protecting the plants from rain and dust),
of a current of air freed by washing from all combined Nitrogen, or of a fixed
and limited quantity of air, too small to be of any avail so far as its compounds of
Nitrogen were concerned. And finally—

To determine the amount of combined Nitrogen in the plants produced, and in the
soil, pot, &c., and, so, to provide the means of estimating the gain or loss of Nitrogen
during the course of the experiment.

MDCCCLXI. 58 Q

448 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

A.—M. BovssINGAULT’S EXPERIMENTS.

1. M. Boussincautt’s experiments in 1837 and 1838, in which the plants were allowed
free access of air, but were protected from rain and dust.

In 1837* BovssinGauLt grew, in burnt soil, watered with distilled water, and with
the access of free air, a pot of Trifolium for two months, and another for three months;
also a pot of Wheat for two months, and another for three months.

The total Nitrogen in the seeds sown in the two experiments with 7rifolium, amounted
to 0°224 gramme. The Nitrogen in the produce, soil, pot, &c., amounted to 0-276
gramme. ‘There was a gain, therefore, of 0°052 gramme of Nitrogen = nearly 20 per
cent. of the total Nitrogen of the products. The development of vegetable matter,
implying, of course, the assimilation of carbon, hydrogen, and oxygen, was, however,
in a much greater proportion; the dry matter of the produce in the two experiments
amounting to nearly three times that of the seed sown.

In the two experiments with Wheat, the total Nitrogen in the seed was estimated at
0-100 gramme. ‘The Nitrogen in the products was exactly the same amount. In the
case of the Wheat, there was, therefore, no gain of Nitrogen indicated. Nevertheless
the dry matter of the produce amounted to nearly double that of the seed.

In 1838+, BovssINGAULt, in a similar manner, sowed Peas containing 0°046 gramme
Nitrogen. The plants obtained; yielded flowers and ripe seed, and their dry matter
was more than four times as much as that of the seed sown. The Nitrogen of the total
products amounted to 0°101 gramme. Here again, therefore, the Leguminous plants
seemed to gain Nitrogen from some undetermined source.

BovssINGAULT made experiments in the same year (1838), with Trifolium, and with
Oats. In these cases, he commenced with carefully selected plants instead of with seeds.
The Zrifolium nearly trebled its total vegetable matter during growth; and it gained
0-023 gramme of Nitrogen out of 0-056 gramme in the total products. The Oat, on the
other hand, indicated only 0:053 gramme Nitrogen in the total products, whilst it was
estimated that there was 0-059 gramme contained in the plants taken for the experi-
ment. The total vegetable matter was, however, doubled.

The substance of M. BousstNéavLt’s conclusions from the above experimental results,
may be stated as follows:—That under several conditions, certain plants seem adapted
to take up the Nitrogen in the atmosphere; but that it was still a question, under what
circumstances, and in what state, the Nitrogen was fixed in the plants. He submitted
—that the Nitrogen might enter directly into the organism of the plant, provided its
green parts were adapted to fix it; that it might be conveyed into the plant in the
aérated water taken up by its roots; that, as some physicists suppose, there may exist
in the atmosphere an infinitely small amount of ammoniacal vapour. He further
suggested that the gain of Nitrogen beyond that supplied in manure, which he had
observed in agricultural production on the large scale, and which he thought evidently

* Ann. de Chim. et de Phys. sér. 2. tome Ixvii. 1838. + Ibid. tome Isix.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 449

came from the atmosphere, might be partly due to Nitrate of Ammonia produced by
electrical action and brought down by rain.

2. M. Boussineauut'’s experiments in 1851, 1852, and 1853, im which the plants were
confined in limited volumes of air*.

BovssinGauLt resumed the subject of the sources of the Nitrogen of vegetation in
1851. His object was, apparently, to settle more definitely, whether plants assimilated
Nitrogen from any other source than the combined forms of it.

In his experiments in 1851 and 1852, Boussmveavr confined his experimental plants
under a glass shade of about 35 litres capacity, which shut off the free access of external
air by resting in a lute of sulphuric acid. ‘Tubes passed under the shade for the supply
of carbonic acid, and water, as they might be needed. Pumice-stone, coarsely powdered,
washed, ignited, and cooled over sulphuric acid, served as soil. To this, at the com-
mencement, some of the ash from farm-yard manure, and also from seed of the kind to
be sown, was added.

In 1851, a Haricot was grown under these conditions, the seed of which, when sown,
was estimated to contain 0:0349 gramme of Nitrogen. After two months of growth,
flowers being formed, the dry substance of the plant was more than double that of the
seed sown; and the total products yielded only 0:0340 gramme of Nitrogen. There
was, therefore, apparently a slight loss of Nitrogen, which amounted, however, to less
than a milligramme. In 1852, two Haricots, sown respectively in separate pots, con-
tained, together, 0:0455 gramme Nitrogen. ‘They were each allowed to grow for three
months, during which time the dry substance was nearly doubled; and in one instance
cpen flowers were formed. The products of both experiments taken together yielded
to analysis only 0:0415 gramme of Nitrogen. ‘There was an apparent loss, therefore, in
the two experiments, of 4 milligrammes of Nitrogen. It is seen, then, that in these new
experiments with Leguminous plants, in which the free circulation of atmospheric air
was not permitted, there was not the apparent gain of Nitrogen that had been met with
in BovssInGatut’s early experiments (in 1837 and 1838), in which free access of air into
the enclosing apparatus was allowed.

In 1851, ten seeds of Oats, and in 1852 four, were experimented upon in a similar
manner. In both cases there was an apparent very slight loss of Nitrogen. In the first
case the Oats vegetated for two months, and in the second for 24 months; and in the
latter, the plant arrived at the point of shooting forth the ear.

In 1853, the apparatus adopted by BoussinGautr consisted of a large globe, or carboy,
of white glass, having a capacity of 70 or 80 litres. At the bottom of this vessel, a
matrix of pumice-stone (or burnt brick) and ashes, prepared as in the last series, was
placed to serve as soil. This was watered with distilled water, and then the seeds were
sown. The neck of the vessel was then closed with a cork, through a perforation in
which, a flask of carbonic acid was inverted, whose aperture, opening into the globe, was

* Ann. de Chim. et-de Phys. sér. 3. tome sli. 1854. :
3Q2

450 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

somewhat contracted. Finally, access of air from without was excluded by bandages
of caoutchoue, which were so secured as to render the whole apparatus air-tight.

In such an apparatus, BoussinGaAuLt made five separate experiments with White
Lupins. In all he sowed thirteen seeds, which were estimated to contain, together,
02710 gramme of Nitrogen. The experiments extended over periods varying from six
to eight weeks. In one instance, burnt brick instead of pumice-stone was used as the
soil; and in this case, as well as in one where pumice was used, bone-phosphate as well
as ashes was added as manure. The dry matter of the produce was about three times
as much as was contained in the thirteen seeds sown. ‘The Nitrogen in the total pro-
ducts of the five experiments amounted to 0°2669 gramme. There was, therefore, a
loss, in the five experiments taken together, of about 4 milligrammes of Nitrogen. In
two of the cases there was a slight gain of Nitrogen, but in neither instance did it
amount to 1 milligramme.

In a similar apparatus, two experiments were made with Dwarf Haricots, a single seed
only being sown in each case. One of the experiments extended over two months, and
the other oyer two anda half months. In both instances flowers were formed, and in
one of them seed. The dry matter of the produce was three to four times as much as
that of the seed sown. ‘Taking the two experiments together, the Nitrogen contained
in the seed was estimated at 0:0652 gramme; and that found in the products amounted
to 0:0637 gramme. ‘There was a loss, therefore, of 1} milligramme of Nitrogen.

There was, then, in this third series of experiments with Leguminous plants, again
rather a loss than a gain of Nitrogen,—the supplies of it in this case being confined to
the combined Nitrogen contained in the seeds sown, and to the free or uncombined
Nitrogen in the fixed and limited volume of air within the apparatus.

Still in the same apparatus, BoussinGavuLt sowed Garden Cress. Thirteen seeds were
sown, all of which germinated, but three plants only survived. The growth of these
extended over three and a half months; and flowers and seed were produced. ‘The
Nitrogen in the products amounted to precisely as much as was estimated to be con-
tained in the thirteen seeds sown.

The last experiment in this closed globular apparatus was as follows: Two White
Lupins were sown to grow; and eight others were applied as manure, after treatment with
boiling water to destroy their powers of germination. The experiment continued for a
period of between four and five months. The dry matter of the produce was nearly twice
as much as would be contained in the ten seeds involved in the experiment. The whole
ten seeds were estimated to contain 0:1827 gramme of Nitrogen; whilst the total pro-
ducts yielded only 0:1697 gramme. The loss of Nitrogen was here, therefore, 15 milli-
grammes; or about one-fourteenth of the whole amount involved in the experiment.
BovsstNGAvtt considered that the loss was probably due to free Nitrogen being given off
in the process of decomposition of the organic matter employed as manure.

In order to ascertain whether the limitation of growth in the foregoing experiments
was due to the limitation in the amount of air, or to a deficiency of available Nitrogen
in the matters used as soil, BoussInGAULT sowed Cress in a good soil, placed the vessel

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 45]

in a limited atmosphere, and supplied carbonic acid. The result was, that the plants
thus grown, in a limited atmosphere, but in a good soil, were even more luxuriant than
a parallel set, grown in a similar soil, in the open air. In both cases a large quantity
of seed was produced.

3. M. BoussinGauLt’s experiments in 1854, with a current of washed air*.

In this series of experiments, BoussinGAvLt supplied his plants with a current of air,
previously washed by passing first through vessels containing pumice-stone saturated
with sulphuric acid, and then through water. He also supplied carbonic acid from
bicarbonate of soda acted upon by sulphuric acid,—the gas evolved being passed first
over chalk, then through a solution of carbonate of soda, and lastly over pumice-stone
saturated with a solution of carbonate of soda. The enclosing apparatus consisted of a
metal-framed glass case of 124 litres capacity, which was cemented down upon a
polished iron plate, upon which the experimental pots were placed. Across one side of
the case was a metallic joint-bar, in which were apertures for the insertion of tubes for
the admission of the washed air, and for the supply of water and carbonic acid. On the
opposite side was a similar joint-bar, to an aperture in which, a tube was attached con-
necting the case with an aspirator of 500 litres capacity. By this apparatus, therefore,
the plants could be supplied with a current of air freed from ammonia, with water, and
with carbonic acid, at pleasure. During the experiment, the atmosphere in the Case
generally contained from 2 to 3 per cent. of carbonic acid. Lastly, by means of one of
the apertures any withered leaves were removed as they fell from the plants; and they
were then dried and preserved for analysis with the remainder of the products.

One of the experiments made in this apparatus was with a single Lupin, which was
allowed to grow for two and a half months. The dry matter of the produce was more
than six times that of the seed. The Lupin sown was estimated to contain 0-0196
gramme of Nitrogen. The Nitrogen found in the products amounted to 0-0187 gramme.
There was a loss, therefore, of nine-tenths of a milligramme of nitrogen.

Four experiments were made with Dwarf Haricots, in three of which single seeds, and
in the fourth two seeds, were sown. One experiment lasted over two and a half months,
and the plant flowered ; one over three months, and the plant seeded ; one over three and
a half months, in which case also the plant seeded; and another over three and a quarter
months. The dry substance of the produced plants was from three to four times as much
as that of the seed sown. ‘The total Nitrogen in the five seeds employed in the four expe-
riments was estimated at 0:1672; the Nitrogen found in the total products amounted to
01661 gramme. There was therefore, upon the whole, a loss of 0-0011 gramme of Ni-
trogen. In two of the experiments there was a loss of 1 milligramme each of Nitrogen ;
and in the other two a gain, amounting to less than 1 milligramme in each case.

In the next experiment, one Lupin seed was sown to grow, and another was steeped
in hot water and applied as manure. The dry matter of the produce from the one seed
amounted to nearly three times that of the two seeds employed in the experiment. The

* Ann. de Chim, et de Phys. sér, 3. tome xliii. 1855.

452 . MR. J.B. LAWES, DR. GILBERT, AND DR. PUGH ON

total Nitrogen in the two seeds was estimated at 0:0355 gramme. That found in the
products was 0:0334 gramme. ‘There was a loss, therefore, of 0-0021 gramme Nitrogen.

Lastly, forty-two seeds of Cress were sown, twelve of which served as manure. Many
of the plants seeded. ‘The dry matter of the produce was more than five times that of
the seed. The Nitrogen in the forty-two seeds was estimated at 0-0046 gramme. ‘That
found in the products amounted to 0-0052 gramme. There was a gain, therefore, of
00006 gramme, or little more than half a milligramme of Nitrogen.

The whole of these experiments in 1854, in which a current of air was supplied to the
plants, taken together, indicated a slight loss of Nitrogen. This was the case, notwith-
standing that all the plants, excepting the Cress, were of the Leguminous family.

4, M. Boussincavult’s experiments in 1851, 1852, 1858, and 1854, in which the Plants
were allowed free access of air, but were protected from rain and dust *.

Contemporaneously with the several series of experiments above described, Bovs-
SINGAULT grew plants simply covered with a case, in such a manner as to exclude any
material amount of dust, but so as to allow of the free access of the external air.

Single Haricots were grown in the manner here described, m the seasons of 1851,
1852, 1853, and 1854, respectively. All four plants flowered; one podded; and one
seeded. The Nitrogen in the seed of the four experiments amounted to 0°1175 gramme.
That found in the vegetable produce, soil, &c., was 0°1258 gramme. There was a total
gain of Nitrogen, therefore, under these circumstances, of 0-0065 gramme. In one case
there was an apparent loss of Nitrogen of a little more than 2 milligrammes; in the
three others the gain was about equal. The dry matter m the produce amounted to
from three to four times as much as that in the seeds sown.

Tn the seasons of 1853 and 1854, three experiments of the same kind were made with
White Lupins. The dry matter of the produce was from three to four or more times as
much as that in the seed. The Nitrogen in the seed of the three experiments taken
together amounted to 0-0780 gramme. That m the total products was 0-08735 gramme.
Here again, therefore, there was a gain of Nitrogen—amounting in this case, in all, to
between 9 and 10 milligrammes.

Under similar conditions, Oats were grown in 1852 which yielded seed. The Nitro-
gen sown was 0:0031 gramme. That in the products was 0:0041 gramme. ‘There was
a gain, therefore, of 1 milligramme of Nitrogen.

In like manner, five seeds of Wheat were sown in 1855. The dry matter of the pro-
duce was more than three times that of the seed. The Nitrogen in the seed was esti-
mated at 0°0064 gramme. That in the products was 00075 gramme. The gain was,
therefore, 0-0011 gramme.

Lastly, 210 seeds of Cress were sown in 1854. Many of the plants seeded ; and there
was, of course, a considerable gain of dry matter. The Nitrogen in the seed was 0°0259
eramme. That in the products amounted to 0-0272 gramme. There was a gain, there-
fore, of 0-0013 gramme.

--* Ann. de Chim. et de Phys. sér. 8. tome xiii. 1855.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 453°

Taking all these experiments together, in which the plants were shaded from rain and
dust, but still allowed free access of air, the total gain of Nitrogen was 0-0192 gramme
upon (-2307 gramme supplied in the seed sown. There was a gain of Nitrogen, therefore,
equal to about one-twelfth of that. sown in the seed. Bovussiveavuur considered that
part of the gain was due to organic corpuscles, and part to the ammonia in the atmo-
sphere. He also considered that, bearing in mind the circumstances of the experiment,
the gain was not sufficiently great to justify the conclusion that there had been any
assimilation of the free or uncombined Nitrogen of the air.

5. M. Boussineauttr’s collateral experiments to control and explain his results*.

In order to ascertain the amount of Nitrogen that might be introduced into the mate-
rials under experiment when the matter used as soil, &c. was not excluded from the
air whilst cooling after ignition, or when free access of air was allowed during the whole
period of vegetation, BoussINGAULT instituted the following experiments.

Sand, powdered brick, powdered bone-ash, and wood-charcoal were each exposed to the
air for two or three days after being ignited, and then the Nitrogen determined in them.
The result was that, after this exposure, a kilogramme of sand gave 0:5 milligramme,
a kilogramme of powdered brick 0-5 milligramme, a kilogramme of powdered bone-ash
0-84 milligramme, and a kilogramme of wood-charcoal 2°9 milligrammes of ammonia.

In order to test the influence of the organic corpuscles of the atmosphere, a pot of
burnt sand, with ashes, the whole moistened with water, was so arranged under a shade
as nevertheless to allow free access of air, and it was so exposed for two and a half
months. At the end of this period small spots of cryptogamic vegetation were visible
on the surface of the sand; but the whole yielded only 0-74 milligramme of Nitrogen.

Again, BoussincauLt found that unless the ashes used as manure were burnt until
nearly all apparent traces of carbon were destroyed, they were liable to retain more or
less and sometimes material amounts of Nitrogen. In some imperfectly burnt ashes
cyanides, and in some, ferrocyanides were found; in others the Nitrogen seemed to exist
in neither of these conditions.

With regard to the much larger gain of Nitrogen indicated in his early experiments
in free air (1837 and 1858) than in those made more recently, BousstnGauLt remarks
that the result may be partly due to the comparatively defective methods of analysis at
the early date, and partly also to the distilled water used for watering the plants con-
taining some ammonia. For, at the time of his first experiments, he was not aware of
the fact, since learned in his analyses of rain and other waters, that water distilled
from that which contained minute quantities of ammonia did not come over free from
it until about two-fifths of the whole had been drawn off.

It will be observed that, in most of the experiments of BoussrneauLt thus far passed
in review, he limited the supply of Nitrogen to the plants to that contained in the seed
sown, and to that which they could obtain from the atmosphere, either washed or un- ;

* Ann. de Chim. et de Phys. sér.. 3: tome sliii. 1855.

454 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

washed, in which they grew. In no case among those experiments in which the
modern refinements of analysis were had recourse to did he find, either with Legumi-
nous or with other plants, such a gain of Nitrogen beyond that supplied in the seed, as
could lead to the conclusion that the free or uncombined Nitrogen of the atmosphere
had been assimilated. In many of the instances the plants yielded not only flowers but
seed; and hence it might be concluded that the conditions provided were adequate for
the performance, by the plant, of the complete course of its natural functions of growth.
Still it might be objected that the vigour of growth was somewhat limited, and that,
under these circumstances, the plant might well refuse to perform the, perhaps, difficult
office of assimilating a very refractory elementary body. In a few instances, seeds whose
germinating power had been destroyed were supplied as manure. In these cases the
amount of Nitrogen assimilated by the plants was much greater than that contained in
the living seed sown ; and the luxuriance of growth was consequently comparatively great.
Nevertheless, instead of a gain, there was generally a loss in the total amount of com-
bined Nitrogen, which was considered to be due to the evolution of free Nitrogen by the
decomposing manurial matter. To get increased vigour of growth—to avoid, if possible,
a loss of Nitrogen such as is above supposed—and, at the same time, to determine whe-
ther or not the Nitrogen of Nitrates were really assimilable by plants—BovssinGavuLt
has latterly made some experiments in which Nitrates were employed as manure, a brief
notice of the results of which should be here given.

6. M. Boussincavit’s experiments in which he supplied combined Nitrogen
in the form of Nitrate of Potash, or Soda*.

In 1855 BoussinGauLt made one experiment with Helianthus in which he supplied
no nitrate to the soil, and another in which a small known quantity of Nitrate of Potash
was employed. In a third experiment Cress was grown in a manured soil, in a fourth
in a soil destitute of combined Nitrogen, and in a fifth in a soil to which a known quan-
tity of Nitrate of Soda was added. In the case of the manured soil, and in the two
cases where Nitrate was employed, there was a very considerable increase in the assimi-
lation of carbon; and there was also much more Nitrogen assimilated than was supplied
in the seeds sown. ‘The increased assimilation of Nitrogen where Nitrate was used, did
not, however, exceed that supplied in the manure. BovssinGautt concluded that the
gain of Nitrogen was to be attributed to the Nitrogen of the Nitrate.

Lastly in regard to BoussiNGAvLr’s experiments: In 1858+ he resumed the question of
the action of Nitrates upon vegetation. He grew two separate pots of Helianthus, two
seeds being sown in each pot. ‘The soils were composed of sand and quartz well washed
from saline matter and ignited. To one pot Nitrate of Potash containing 0-0111 gramme
of Nitrogen, and to the other Nitrate containing 0-0222 gramme Nitrogen, was added.
In the first case, he did not get back, in the plant, soil, and pot, the Nitrogen of the
seed and Nitrate by 0:0014 gramme. In the second experiment the loss of Nitrogen
amounted to just 1 milligramme. Bovssincavur found, however, that there remained

* Ann. de Chim. et de Phys. sér. 3. tome xlyi. 1856. + Compt. Rend. tome slyii. 1858.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 455

in the soil an amount of carbonate of potash very nearly corresponding in potash to
the amount of nitrate of potash which would represent the observed loss of Nitrogen.
He concluded that nitrate had been decomposed in the soil, by the organic matter of
the débris of the seeds and of the roots, and that Nitrogen had been evolved. If we
clearly understand this explanation of the loss of Nitrogen of the nitrate, we would
suggest that it would seem to require for its validity that the plant should have assimi-
lated potash from the nitrate exactly corresponding in amount to the Nitrogen it fixed
from the same source.

From the results of these experiments with nitrate, BoussincAuLtT drew the following
conclusions :—

1. That there was no assimilation of free Nitrogen.

2. That there was a loss of supplied Nitrogen, either from the soil, or by the plant.

3. That, in the two cases, the amount of carbon assimilated bore a close relation to
that of the Nitrogen taken up by the plant.

It is seen, then, that the results of the laborious investigations of BoussiNGAULt,
extending at intervals over a period of more than twenty years, have led him to con-
clude that, neither Leguminous plants, nor the others experimented upon, were able,
either when their supplies of combined Nitrogen were limited to that contained in the
seed sown, or when their vigour of growth was stimulated by artificial supplies of com-
bined Nitrogen, to assimilate the free or uncombined Nitrogen of the atmosphere.

B.—M. G. Vitie’s ExperimMents*.
1. M. G. Vittx’s determinations of the Ammonia in the atmosphere.

M. G. VitiE, of Paris, commenced his investigations, on the subject of the assimilation
of Nitrogen by plants, in 1849. He first sought to determine the proportion of
Ammonia in the atmosphere. ‘To this end, he aspired known quantities of air through
acid, and determined the amount of ammonia absorbed. He operated upon very much
larger volumes than previous experimenters had done. His results show, moreover, a
much smaller proportion of ammonia in the air than those of others.

The air of Paris, during part of 1849 and part of 1850, gave a mean of only 0:0237
part by weight of ammonia, to 1,000,000 parts by weight, of air; and that of the
suburbs of Paris, during some period of 1852, gave 0:0211 parts of ammonia, to
1,000,000 parts of air.

2. M. G. VILLE’s general plan of experimenting on the question of the assimilation
of Nitrogen by plants.
M. G. Vitte employed specially-made porous flower-pots, and used, as soil, washed

* Recherches Expérimentales sur la Végétation, par M. Grorgrs VILLE. Paris, 1853.
MDCCCLXI. SR

456 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

and ignited sand, sand and brick, or sand and charcoal, with the addition of the ash of
the plant to be grown. He planted seeds or plants, the composition of which was esti-
mated by the analysis of parallel specimens. Several pots were for the most part
enclosed in an iron-framed glazed case of 150 litres (or more) capacity, through which a
current of air equal in amount to several times the volume of the vessel was aspired
daily. Carbonic acid and distilled water were supplied as needed. In some cases the
air admitted into the apparatus was only preyiously freed from dust; and then the
amount of atmospheric ammonia that would be brought in was calculated according to
the determination of the proportion of ammonia in the air, above alluded to. In other
cases the aspired air was previously freed from ammonia by washing. In some experi-
ments, ammoniacal gas was passed, in known quantities, into the air of the apparatus.
Lastly, others were made, in which combined Nitrogen was added to the soil in the form
of nitrate, or of ammonia salts; and in these cases the plants were allowed to grow in
free air, only shaded from rain and dust.

3. M. G. ViLLE’s experiments in 1849 and 1850, in which the plants were supplied
with a current of unwashed air.

In 1849, sand was used as soil; three pots of plants were grown for two months;
namely, one of Cress, one of large Lupins, and one of small Lupins. The air admitted
into the apparatus was not previously deprived of its natural ammonia. ‘The dry sub-
stance of the produced Cress plants amounted to more than sixteen times that of the
seed sown. The Nitrogen in the Cress seeds amounted to 0:026 gramme; that in the
products to 0-147 gramme. ‘The Nitrogen in the products was, therefore, between five
and six times as much as that in the seed; and the actual gain of it amounted to 0121
gramme. In the case of the large Lupins, the dry matter of the produce was about
31 times as great as that of the seeds sown; but there was neither gain nor loss of
Nitrogen. ‘The small Lupins gave 23 times as much dry substance in the produce as
was supplied in the seeds; and of the Nitrogen of the seeds sown, there was an apparent
loss of rather more than one-fourth, during the experiment.

....The total gain of combined Nitrogen in the apparatus, taking the three experiments
.together, was 0-103 gramme. The Nitrogen in the ammonia of the current of unwashed
air, was, however, estimated at only 0:001 gramme. M. G. VILLE concluded, therefore,
that the Cress had appropriated a considerable quantity of the free or uncombined
Nitrogen of the atmosphere.
.. The plants experimented upon in 1850, were Colza, Wheat, Rye, and Maize. Inthe
case of the Colza, the experiment commenced with young plants, but in the other cases
with seed. The four pots were placed in an apparatus similar to that used before, and
the conditions supplied were also the same as in 1849.
The dry matter of the produced Colza plants amounted to between forty and fifty
_ times as much as that of the young plants when taken for experiment. The Nitrogen
was also increased more than forty-fold. The dry matter of the Wheat plants was about

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 457

four times that of the seed sown; and the Nitrogen in the total products was nearly.
double that in the seed. _The dry substance of the produced Rye plants was five times,
and their Nitrogen nearly three times that of the seed. In the experiment with Maize,
the dry matter increased only about three times, but the Nitrogen nearly 43 times.

The actual gain of Nitrogen in the total products of the four experiments, was 1:1803
gramme. The whole admitted in the form of atmospheric ammonia was estimated at
0-0017 gramme, or less than 2 milligrammes. M. VILLE remarks, moreover, that an
examination of the distilled water before being used to water the plants, and of the
water afterwards removed from the apparatus, showed more ammonia in the latter than
intheformer. The conclusion from this second series of experiments also was, therefore,
that a considerable quantity of free or uncombined Nitrogen had been assimilated.

4, M.G. VILLE’s experiments in 1851 and 1852, in which the plants were supplied
with a current of air washed free from ammonia.

In 1851, one pot of Sun-flower, from seed, and two pots of Tobacco, starting from
plants transplanted from good soil, were grown together, under circumstances similar to
those of the preceding experiments, with the exception that now the air was deprived
of its ammonia by passing over pumice-stone saturated with sulphuric acid, and also
through a solution of bicarbonate of soda, previous to entering the apparatus.

The Sun-flowers gave 95 rudimentary grains; but the Tobaccos did not flower. How-
ever, taking the three experiments together, the dry matter increased nearly 200-fold,
and the Nitrogen increased nearly 40-fold, during a period of growth of three months.
The total gain of Nitrogen in the apparatus was 0-481 gramme.

In 1852, the conditions of the apparatus were the same as in 1851. The selection of
plants was as follows:—One pot of Autumn Colzas, starting with young plants; one of
Spring Wheat, from seed; one of Sun-flower, from seed; and two of Summer Colzas,
from plants.

In every case the dry matter of the produce was many times that of the young plants
or seed. In the case of the Sun-flower, it was more than 100 times that of the seed.
In each experiment, there was of Nitrogen, also, much more at the conclusion, than at
the commencement. In the experiment with Autumn Colzas there were 4:7 times,
in that with Spring Wheat 2-2 times, in that with Sun-flower 25°5 times, in one with
Summer Colza 3-4 times, and in the other with Summer Colza 6:7 times as much
Nitrogen in the total products as in the original plants or seeds. The total amount of
Nitrogen gained in the five experiments, was 1:624 gramme, which was 5:3 times as:
much as was contained in the total original plants and seeds.
_ To show the degree of luxuriance of growth of the different descriptions of plant, it.
may be mentioned that the Winter Colzas flowered, but gave no seed; the Sun-flower
gave 412 rudimentary grains; and the Wheat seeded completely, giving 47 grains. The
Summer Colzas had little tendency to go to seed, but developed a great deal of leaf; and
hence it was, it was supposed, that they gained large actual amounts of Nitrogen.

3R2

458 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

5. M. G. Vinun’s experiments in which known quantities of Ammonia were admitted into
the atmosphere of the enclosing apparatus.

ad

In each of the three seasons 1850, 1851, and 1852, M. G. Vitte had a duplicate
apparatus, enclosing, in each case, similar plants to those in the other, but with this
difference in the conditions—that ammonia was supplied to the atmosphere of the
second apparatus. As might be expected, the increase, both in dry substance, and in
Nitrogen, was much the greater, in relation to the amounts of them contained in the
seed or young plants, when ammonia was thus employed. In no case, however, did the
plants take up Nitrogen equal in amount, much less exceeding, the whole of that sup-
plied to the air in the combined form, as ammonia. The results have not, therefore, so
direct a bearing on the question of the assimilation of free or wncombined Nitrogen, as
to require that we should quote them in any detail. Their chief interest was in show-
ing the influence of ammoniacal supply, not only upon the vigour and luxuriance of
growth generally, but upon the order, or course of development, of the plants, according
to the stage of growth at which the application was made.

6. Comparison of M. G. Viuur’s results with those of M. Boussrxcavit up to 1853
inclusive.

It will be remembered that, up to 1853 inclusive, M. Bousstncavt’s experimental
plants had been grown either in free air—in which case they had fixed, from some source,
slightly larger amounts of Nitrogen than were contained in the seed,—or in fixed and
limited volumes of air (carbonic acid being added), in which cases no gain of Nitrogen
was observed. The gain of Nitrogen in the free air was, moreover, considered to be too
small to indicate, under all the circumstances, any assimilation of free or uncombined
Nitrogen. On the other hand, M. G. Vitir’s experiments up to the same period had
indicated an enormous gain of Nitrogen. The Nitrogen in the products, indeed, some-
times amounted to more than forty times that contained in the seed.

Results so strikingly contradictory could hardly fail to excite great attention and
interest among Chemists and Vegetable Physiologists. But M. Vitue’s plants had been
grown in a constant current of renewed air, and not in only a fixed and limited volume
of it. This fact, and some other points, were alleged to account for the difference in
result. At any rate, on the one hand, M. BousstnGauLT commenced in 1854, to expe-
riment with a current of air; whilst, on the other, a Commission, composed of Members
of the Academy of Sciences of France, was appointed to superintend the conduct of a
new set of experiments by M.G. Vittr. It has already been shown, that M. Bovssin-
GAULT's new experiments in which a current of air was employed, did not indicate any
assimilation of free or uncombined Nitrogen, any more than did those in which the
plants had grown in limited volumes of air only.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 459

7. M. G. Vinte’s experiments conducted under the superintendence of a Commission
comprising MM. Dumas, Reanavutt, Paven, Decaisne, PeLicot, and CHEVREUL.

These experiments were conducted at the Muséum d'Histoire Naturelle, Jardin des
Plantes, Paris, in the autumn of 1854. M.Ctorz was appointed to assist M. VILLE;
and M. Curvrevtn reported on behalf of the Commission, in 1855*.

In an apparatus similar to that employed in the experiments of M. Vite which have
been already described, three pots of Cress were placed. The soil consisted of ignited
brick and sand, to which was added some of the ash of the plant. Carbonic acid
was supplied artificially ; and the plants were watered with distilled water. ‘The Cress
in one of the pots did not thrive well; and, in this case, analysis showed a loss of
2 milligrammes of Nitrogen. In one of the other cases, there was a gain of 0°0492
gramme of Nitrogen, upon 0:0038 gramme supplied in the seed; and in the other,
there was a gain of 0:0071 gramme of Nitrogen, upon 0-0039 gramme contained in the
seed.

At the suggestion of one of the members of the Commission, a smaller vessel was also
attached to the aspirator, in which one pot sown with Cress was placed. ‘The soil being
duly watered with distilled water, the apparatus was then closed, and not opened (as
the other frequently was) until the conclusion of the experiment. In this case also,
there was a considerable gain of Nitrogen indicated, namely, 00287 gramme gain, upon
0:0063 gramme in the seed.

Unfortunately, an element of uncertainty attached to the evidence afforded by these
experiments made under the superintendence of the Commission, which is very much to
be regretted. A quantity of distilled water taken from the same bulk as that used for
watering the experimental plants was saved for analysis. The examination of this
water devolved on M. CLorz; who, unfortunately, was called away for some days, during
the evaporation of the water with oxalic acid, with a view to the after-determination of
any ammonia it might contain. M. Peticor determined the ammonia in the acid residue
of the evaporation of this water, as well as in that of the water removed from the cases,
after it had served in the experiments. ‘The result was, that there was indicated such
an excess of ammonia in the water before being used, over that in the residual water
after removal from the larger case, as more than covered the increase in the Nitrogen
of the plants over that in the seeds sown. M.Cuorz found, however, that, in his
absence, the evaporation of the water had been conducted by the side of ammoniacal
emanations from other processes. But when new portions of the original water were
evaporated with proper precautions, less ammonia was indicated in it than in the water
at the close of the experiment; and then, also, a gain of Nitrogen by the plants in the
larger apparatus was indicated.

At any rate, however, the result with the single pot, in the small apparatus, showed
a considerable gain of Nitrogen, even supposing the first analysis of the supplied water
to be correct.

* Compt. Rend. 1855.

460 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

From the result of the whole inquiry, the Commission announced the following con
clusion :—

That the experiment made at the Muséum @ Histoire Naturelle by M. Viuum, is con-
sistent with the conclusions which he has drawn from his previous labours.

8. M. G. Vitun’s experiments in which the plants were exposed to free air, and Nitrates or
Anumonia salts were employed as manure*.

In 1855 and 1856, M. G. Vitis conducted a series of experiments with the double
object, of investigating the action of nitrates upon vegetation, and of still further
examining into the capability of plants to assimilate the free or uncombined Nitrogen
of the atmosphere. The whole of the experiments now in question were made in free
air, the plants being only shaded from rain; that is to say, without any enclosing appa-
ratus, or artificial current of air and supply of carbonic acid. ‘The soils consisted of
calcined sand; ashes of plants such as those to be grown were added; and distilled
water was used for watering. Colza and Wheat were the plants experimented upon.
Lastly, the special conditions of the experiments were, that nitrate of potash in smaller
or in larger quantity, or nitrate of potash and different ammonia salts, in equivalent
quantities so far as their Nitrogen was concerned, were employed.

To the prosecution of this series of experiments, an exact method of estimating minute
quantities of nitric acid was essential. M. VituE succeeded in devising such a method,
which was very favourably reported upon by M. Petovuzer, on behalf of a Commission
composed of MM. Banarp, Peiicor, and PreLowze.

In 1855, two pots, and in 1856 one pot, of Colzas were grown, to each of which
0-5 gramme of nitrate of potash was supplied as manure. By examination of the soil,
the point was ascertained when the whole of the nitrate had been drawn from it by the
plants. The experiment was then stopped; and analysis showed that the total produce
contained almost identically the amount of Nitrogen supplied in the seed and in the
nitrate. The dry vegetable substance was, however, increased about 200-fold.

Again in 1855, two pots of Colzas were sown, to each of which 1 gramme instead of
0:5 gramme of nitrate was added; and in 1856 two more, with the same quantity.
In each of these cases, the produce (which in dry matter was several hundred times that
of the seed) contained considerably more nitrogen than had been supplied in the seed
and in the nitrate. M. G. Viuue’s conclusions were, that the plants had taken up the
nitrate and assimilated its Nitrogen, and that when by the larger supply of nitrate the
growth had been extended, the free Nitrogen of the atmosphere was also assimilated.

In 1855 an experiment was made with Wheat manured with 1:72 gramme of nitrate
of potash. The plants were allowed to mature, and they gave 84 grains. There was
more Nitrogen in the vegetable produce alone, than in the seed and nitrate, and very
much more in the total products, taking into account the residual Nitrogen in the soil.
In 1856, two pots of Wheat were sown, to each of which 1:765 gramme of nitrate were
added. The plants of one pot were taken up at the time of flowering, and they contained

* Recherches Expérimentales sur la Végétation, 1857.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 461

almost identically the same amount of Nitrogen as was provided in the seed and nitrate.
Those in the other pot were allowed to go to seed, and 119 grains were formed. In this
case, again, the Nitrogen in the produce was much more than had been supplied, and
very much more when the residual Nitrogen in the soil and pot was taken into the
calculation. Lastly, on this head, two pots of Wheat (also in 1856) were sown without
nitrate, and two with 0:792 gramme of nitrate to each. ‘There was a considerable gain
of Nitrogen in each of the four cases. ‘The actual amount of gain was greater in the
cases where the nitrate was employed; but the proportion gained, to that supplied,
was greater where no nitrate was used.

To show the comparative efficacy of Nitrogen supplied in different conditions of
combination, the following experiments were made during the season of 1856.

Two pots of Colzas received, each 0-5 gramme of nitrate of potash; and two other
pots of Colzas received each an amount of sal-ammoniac equivalent in Nitrogen to the
0-5 gramme of nitrate. The two experiments with Nitrate gave equal amounts of
Nitrogen in the produce; and the two with sal-ammoniac, also equal amounts. But the
two with nitrate gave more than 1} time as much Nitrogen in the produce, as the two
with sal-ammoniac. In two other experiments, double the quantity of nitrate and
sal-ammoniac, respectively, was employed, and the growth was allowed to extend over a
longer period. ‘The amount of Nitrogen in the produce was, in both these cases, very
much greater in proportion to the amount supplied, than in the preceding experiments
where the smaller amounts of nitrate and sal-ammoniac were used. It was, moreover,
more than three times as much where the nitrate, as where the sal-ammoniac was
employed. There was, too, where the nitrate was used, a considerable amount of
Nitrogen assimilated beyond that provided, in the combined form, in the seed and
manure.

Experiments similar to the above were made with Wheat. Two pots, to each of which
nitrate of potash was added, containing 0-110 gramme of Nitrogen, yielded, respectively,
in produce, 0°218 and 0°224 gramme of Nitrogen. ‘Two pots of Wheat, each manured
with sal-ammoniac, containing also 0:110 gramme of Nitrogen, gave, respectively, in the
produce, 0-161 and 0-124 gramme of Nitrogen. In the same way, nitrate of ammonia
containing 0-110 gramme of Nitrogen gave 0:118 and 0-149 gramme, and phosphate
of ammonia 0-116 and 0:150 gramme of Nitrogen in the matured Wheat plants.

In regard to the experiments of M. VILLE referred to in this Division (8), he remarks,
that the point at which the artificially supplied Nitrogen becomes exhausted is indi-
cated by a lightening of the colour of the leaves, and that it is then that the plants
begin to assimilate the uncombined Nitrogen of the atmosphere. To secure this assi-
milation, he considers that itis not only necessary that the supply of combined Nitrogen,
and the vigour of growth, should reach beyond a certain limit, but that the artificial
supply itself should, on the other hand, not exceed a certain limit. Further, the gain
of Nitrogen in the experiments conducted on the plan now under consideration was so
great, that, bearing in mind previously obtained results wherein the limit of the effect

462 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

of atmospheric ammonia had been ascertained, the influence of that source may, in the
case of these new results, be entirely overlooked.

The fact that a given amount of Nitrogen in the form of combination of a nitrate was
more efficacious than the same amount supplied in either of the ammoniacal salts expe-
rimented upon, was held to show that the nitrate was taken up by the plants as such,
and was not previously transformed into ammonia.

M. Viutr’s experiments, as a whole, thus indicated that plants can take up Nitrogen
in three forms—namely, as nitric acid, as ammonia, and as free Nitrogen. He enume-
rates the following conclusions :—

1. By means of nitre we may prove, without the aid of an enclosing apparatus, that
plants absorb and assimilate the gaseous Nitrogen of the atmosphere.

2. Nitre acts by its Nitrogen. It is absorbed in the state of nitre.

3. In relation to the amount of Nitrogen, nitre is more active than ammonia-salts.

9. M. G. Vitie's collateral experiments to control or eaplain his results*.

M. Vite adduces evidence of yet another kind, in support of his view that plants
assimilate the free Nitrogen of the air. Air was passed through an otherwise closed
apparatus, in which was placed a vessel containing calcined sand, or calcined sand
and decomposing organic matter. In no case was nitric acid formed. Nitrification, the
result of the combination of the oxygen and nitrogen of the air within the porous soil,
was not, therefore, the source of the Nitrogen gained by his experimental plants.

Experiments were made in which a given amount of organic matter (Lupins, Gelatine,
&c.) was mixed with calcined sand, and exposed in an apparatus to a current of air,
which carried the gaseous products into acid, to retain ‘any ammonia that might be
formed. The determination of the Nitr ogen remaining in the matrix, and of the ammonia
given off and absorbed by the acid, showed & loss of Nitrogen, which could only have
passed away in the free gaseous form.

Other vessels of sand were prepared, to which similar known amounts of organic
matter were added, and then seeds of Wheat were sown, the organic matter serving as
manure. When the growth was stopped at a certain stage, almost exactly the same
amount of Nitrogen was found in the Wheat plants and in the sand, &c., as was origin-
ally contained in the seeds sown and in the organic matter added. Assuming that the
decomposition of the organic matter had taken the same course as in the other experi-
ments—free Nitrogen being given off—it was obvious that a corresponding amount of
free Nitrogen had been taken up by the plants. In other cases the growth of the
Wheat was allowed to continue longer than in the experiments just alluded to; and
then the total Nitrogen in the products not only equalled, but considerably exceeded,
that in the seed sown and in the organic manure. In this instance, at least, it could
not be said that the Nitrogen not received by the plant as ammonia had been taken up
by it as nascent Nitrogen evolved in the decomposition.

* Recherches Expérimentales sur la Végétation, 1857.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 463

The general conclusions from this part of the inquiry were as follow :—

1. Organic matters in decomposition lose a part of their Nitrogen as ammonia, and a
part as Nitrogen gas.

2. Vegetation does not interfere with the progress of this decomposition.
. Plants cultivated in a manured soil, give more Nitrogen in their produce than the

ish)

manure yields as ammonia.

4. The excess of Nitrogen in the produce has been absorbed as free gaseous Nitrogen.

In regard to the explanation of the assimilation of free Nitrogen by plants, M. Vinie
calls attention to the fact, that nascent hydrogen is said to giye ammonia, and nascent
oxygen nitric acid, with free Nitrogen; and he asks—Why should not the Nitrogen in
the juices of the plant combine with the nascent carbon and oxygen in the leaves? He
further refers to the supposition of M. pr Luca, that the Nitrogen of the air combines
with the nascent oxygen given off from the leaves of plants, and forms nitric acid. Again,
the juice of some plants (mushrooms) has been observed to ozonize the oxygen of the
air; is it not probable, then, that the Nitrogen dissolved in the juices will submit to the
action of the ozonized oxygen with which it is mixed, when we bear in mind that the
juices contain alkalies, and penetrate tissues the porosity of which exceeds that of spongy
platinum, a body so apt to favour combinations ?

Summary Statement of the results and conclusions of M. BousstnGauut and M. G. VILLE.

M. BovssinGAuLt, when, in his earlier investigations, he grew plants in free air, found
only such indications of a gain of Nitrogen as, in his opinion, may be attributed to
inaccuracies in the methods of experimenting and analysis at the early date, and to the
combined influences of ammonia and organic corpuscles in the atmosphere; and when,
more recently, he grew plants only shaded in such a manner as still to allow the free
access of air, the gain of Nitrogen observed was not more than he considered might be
due to the influences last mentioned. When he grew plants, either in confined and
limited volumes of air, or in a current of air washed free from ammonia and organic
corpuscles, the results did not show any appreciable gain of Nitrogen. Lastly, when
he supplied either decomposing organic matter, or nitrate, to increase the activity of
growth, he did not find such an amount of combined Nitrogen in his products, as to
lead him to conclude that there had been any assimilation by the plants of free or
uncombined Nitrogen. In these cases, indeed, he generally found a loss of combined
Nitrogen during the experiment, supposed to be due to the evolution of free Nitrogen
in the decomposition of the matters used as manure.

The results of M:G. Vine, on the other hand, showed a very considerable gain of
Nitrogen during growth, whether the plants were subjected to a current of unwashed
air, or of ammonia-free air,—and also when the plants were grown in free air, and their
activity of development increased by the use of nitrates, or other nitrogenous matters,
as manure. This gain of Nitrogen he considers to be due to the assimilation of free or
uncombined Nitrogen. It is remarkable, too, that the proportion of Nitrogen gained, to

MDCCCLXI. 38

464 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

. that supplied in the combined form, was observed to be the largest in some of the 8
that lied in the combined form, was observed to be the largest in sor f the case
where no nitrogenous manure was employed, and where the total amount of combined
Nitrogen within the reach of the plants was confined to a few milligrammes only, con-
ained in the original young plants or sceds that were planted. 1 some such instances
t lin tl ginal g plants or ls that were planted. In some such instances,
the amount of combined Nitrogen found in the products was about forty times as much
as was supplied. In other cases, the assimilation of free nitrogen only seemed to ta
pplied. In other cases, tl imilation of fi trog ly 1 to take

place when the activity, and stage of growth, of the plants, had been forced beyond a
certain point by the use of considerable a s of nitrogenous manure.

tain point by the use of considerable amounts of nitrogenous 1 e

Results and conclusions so astonishingly conflicting as those of M. Boussincauur and
M. G, ViLLE, have naturally incited others, either to investigate anew, or to seek, in
the conditions provided in their experiments, for some explanation of the discordance.
Before entering upon the consideration of our own experiments bearing upon the points
in question, it will be desirable to add to the foregoing review a brief notice of the
labours, or opinions, of these other experimenters or arbitrators.

C.—M. MEénr’s Experiments *.

In 1851, M. Mine made some experiments in reference to the assimilation of Nitrogen
by plants. He seems to assume that Boussincauur had concluded from his experiments
that the free Nitrogen of the atmosphere was appropriated by plants; and he refers to
the experiments of M.G. VILLE as confirmatory of such a view. M. Mine made three
sets of experiments in reference to this question.

1. He grew Wheat and Peas, respectively, in powdered glass as soil, allowing them
contact with common air, and watering them with pure water. The Wheat increased
in Nitrogen in amount equal to one-fourth of that contained in the seed sown; whilst
its carbon, hydrogen, and oxygen were double those of the seed. The Pea-plants
doubled the carbon, oxygen, and hydrogen of the seed sown, and their Nitrogen was
threefold that of the seed.

2. Lentils, Peas, Haricots, Beans, Wheat, Rye, and Oats were grown in a sterile
matrix under a bell-glass. They were respectively supplied with an atmosphere of
known composition, and with acetate of ammonia in the soil. The plants increased in
Nitrogen, and the ammonia in the soil diminished; but the free Nitrogen of the air was
not perceptibly affected.

3. This series of experiments was in every way similar to the second, with the excep-
tion that the Nitrogen of the air was replaced by hydrogen. The plants flourished,
and took up some of the acetate of ammonia.

M. Méne concludes that plants do not appropriate the free Nitrogen of the air.

D.—M. Roy’s VIEWS ON THE SUBJECT OF THE ASSIMILATION OF NITROGEN BY PLantsf.

M. Roy gave a paper on this subject in 1854. His supposition was that carbonate of
ammonia constituted the chief source of Nitrogen to plants. Leguminous plants, he
* Compt. Rend. xxxii. + Ibid. xxxix.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 465

considered, appropriated carbonate of ammonia from the atmosphere by their leaves.
Graminaceous crops, on the other hand, he supposed, only took it up in solution by
their spongioles. He further supposed that the free Nitrogen of the air was not appro-
priated by the leaves of plants, but that Nitrogen dissolved in water, and so taken up,
by their roots, could be assimilated. He concluded that, in the case of M. Boussry-
GAULT’s plants grown in limited air, there would be but little passage of solution of
Nitrogen by their roots, and evaporation of water from their leaves, and that, hence, the
necessary conditions did not exist for the assimilation of free Nitrogen. M. VILur’s
rapid current of air would, on the other hand, cause a considerable amount of solution
of Nitrogen to be drawn into the plants.

E.—Tue ExpermMents or MM. CLorz AND GRATIOLET.

In 1850, MM. Ctoxz and Grariotet published the results of some experiments made
with Water-plants. They found that, carbonic acid and air being both present, the
plants gave off oxygen slowly, or very rapidly, according to the condition of the sunlight
and the temperature. In water deprived of common air, but containing carbonic acid,
the evolution of oxygen rapidly declined, Nitrogen was given off, and the plant contained
less Nitrogen than a similar plant in water not deprived of its air. The evolution of
Nitrogen diminished as the experiment proceeded. They considered that, in the vege-
tation of Water-plants, Nitrogen is given off from their nitrogenous constituents and
that there must be restoration either from free or combined Nitrogen. And as their
experiments showed that ammonia-salts were injurious to the plants, they concluded
that they take up free Nitrogen dissolved in water.

In 1855* M. Crorz published the results of some experimental inquiries on nitrifica-
tion, with a view to the question of the source of the Nitrogen of plants. He made
twenty experiments, passing washed air through as many different combinations of
porous, earthy, and alkaline matters. The experiments continued from September 1854
to April 1855, when, in some cases, efflorescence was observed. He found nitrates to
be formed in notable quantity in calcined brick, or pumice, impregnated with alkaline
or earthy carbonates; also, in uncalcined brick similarly impregnated. In chalk, marl,
a mixture of kaolin and precipitated carbonate of lime, &c., only traces of nitrate were
formed.

M. Ctorz concluded that nitrates would be formed when a current of air was passed
over porous bodies, alkalies being present. He considered, therefore, that the porosity
of the pots and brick fragments, the alkalinity of the ashes, the moisture, and the cur-
rent of air, in M. VILLE’s experiments with plants, provided the conditions for the forma-
tion of nitric acid. He asks, can such formation take place in limited air?

F.—Tue Experiments or M. pe Luca.

M. pe Luca found that, on passing moist ozonous air over potash and potassium,
nitrate of potash was formed. He further found that the oxygen given off by plants
* Compt. Rend. xli. + Ibid. 1856.

382

466 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

in sunlight was in many cases ozonous. He aspirated a large quantity of air, in the
neighbourhood of vegetation, through carded cotton, and then through sulphuric acid,
to wash it. The washed air then passed over potassium, and through a dilute solution
of pure potash, when nitrate of potash was formed. When, on the other hand, air in
the midst of habitations was operated upon in a similar way, the formation of nitric
acid was not observed. M. pe Luca supposes the air surrounding vegetation, in sun-
light, to be ozonous; that by its means the Nitrogen of the air may be converted into
nitric acid; and that thus the Nitrogen of the air may be rendered available for assimi-
lation by plants, under the influence of vegetation itself.

G.—Tue Experiments or M. Hartine*.

In 1855, M. Harrine published some criticisms, and the results of some experiments,
on the question of the assimilation of Nitrogen by plants. He considered that the
Nitrogen of the air might contribute indirectly to vegetation. He attributed a forma-
tion of ammonia from the decomposing débris of seeds, &c., and the free Nitrogen of
the air, in the case of M. ViLur’s experiments; and also supposed that nitrie acid
might be formed by the oxidation of the atmospheric Nitrogen. ‘The increase of Nitro-
gen in M. Vinte’s plants, and of ammonia in the water of the enclosing apparatus, was
taken as proof of such formation of ammonia.

M. Hartineé made two sets of experiments, in one of which the plants grew in a limited
volume of air, and in the other in a current of air washed free from ammonia—both
arranged with a view to ayoid the formation of ammonia. He employed enclosing-appa-
ratus somewhat on the plan of M. Boussincautt and M. VILLE; but he used glass vases,
instead of porous pots, for his plants. He grew Beans, Buckwheat, and Oats. After
the seeds had germinated, and the plants had protruded a little above the surface of the
artificial soil, he covered the latter with a mixture of wax and oil, to shut off the access
of air. He further enclosed the stems of the plants in caoutchouc tubes; and inserted
other caoutchouc tubes through the waxy coating, for the supply of water. Some of the
plants were very vivacious at first; and in the case of the Beans, two began to flower ;
but then the leaves turned yellow, and the experiment was stopped. His apparatus
consisted of tinned-iron pans, varnished, and surmounted by glass shades of 18 litres
capacity. ‘There was an aperture for the admission of carbonic acid, another for that of
water, and so on.

The result was that the produced plants yielded no more dry matter than was con-
tained in the seeds. M. Harrine considered, therefore, that the determination of the
Nitrogen was superfluous. The growth evidently stopped when the supplies of the seeds
were exhausted. M. Harrine’s general conclusions on the subject were as follow :—

1. Plants absorb salts of ammonia, and nitrates, by their roots.

2. The Nitrogen of the air contributes to the formation of ammonia, and nitrates, in
the soil.

3. It is not proved that Nitrogen serves directly for the nutrition of plants.

* Compt. Rend. sli. 1855.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 467

H.—M. A. PerzHoLpt on THE SOURCE OF THE NITROGEN OF PLANTS*.

In the years 1852 and 1853, M. H. M. CuLEsoparow made some experiments on the
subject of the assimilation of Nitrogen by plants, at Dorpat, under the direction of
M. Perznoipt, who has reported the results of the inquiry.

M. PerzHonpr assumes that if plants can appropriate the free Nitrogen of the air,
they will not need-ammonia; and that if they take Nitrogen from ammonia, the arti-
ficial supply of the latter will increase growth.

The experiments were made upon Barley. In 1852, an ignited yellow sand was taken
as the soil. To one set of plants, no ammonia was supplied; to a second, carbonate of
ammonia was provided in the soil; and to a third, carbonate of ammonia was supplied
in the air. Both the crops with an artificial supply of ammonia gave three times as
much produce as the crops without such supply. The Nitrogen in the produce was
also very much greater, both in percentage, and in actual amount, where the ammonia
was used.

In 1853, six sets of experiments were made, and as before, with Barley. The soils con-
sisted of an artificial mixture of clay, sand, and felspar, decomposed by heating with
lime. The first set of three pots was provided with this soil alone; the second had,
in addition, 0-13 per cent. of bone-ash acted upon by sulphuric acid; and the third had
1-33 per cent., or ten times as much, of the same phosphatic manure. The three other
sets were, respectively, so far like the three just described, but in addition ammonia
was artificially supplied to the atmosphere in which the plants grew. The phosphatic
manure, whether with or without the ammoniacal supply, much increased the produce
of both corn and straw. The Nitrogen of the crops was also very much increased in
actual amount (though diminished in percentage in the dry substance) by the aid of
the phosphatic manure; and the actual amount of Nitrogen was still further creased
by the addition of ammonia to the atmosphere of the plants; and the percentage of
Nitrogen in the dry substance was also greater where the ammonia was supplied, than
in the corresponding cases without it. The experiments without ammonia were made
in free air. The Nitrogen in the produce was about seven times that of the seeds where
no phosphates were employed; about twelve times that of the seed witn the smaller
quantity of phosphate; and about twenty times that of the seed with the larger amount
of phosphate.

M. PetrzHo.pt considered it difficult to account for the fact of M. BoussineauLr get-
ting little or no increase of Nitrogen when he grew plants in free air, which must have
supplied some ammonia, even though rain and dew were excluded. He thinks the error
must be on the side of M. Boussineau.r.

It is seen that the explanations or conclusions of these several arbitrators are nearly
as conflicting as those of M. Boussincautr and M. G, VILLE themselves. )
For ourselves we are free to confess that we are unable to discover, either in the

* Journ. fiir Prakt. Chem. Band Ixy.

468 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

differences of plan adopted by M. Boussincauit and M. G. Vitix, so far as they have
themselves described them, or in the results and explanations of other experimenters,
any satisfactory solution of the difference of result arrived at. A priori, there are reasons
for concluding, both from the chemical characters of Nitrogen itself, and from what we
at present know of the chemistry of vegetation in other respects, that plants would not
assimilate Nitrogen offered to them in the free state. On the other hand—to say
nothing of the large total amount of combined Nitrogen actually existing—the sta-
tistics of Nitrogen-production show that there is an amount of Nitrogen periodically
available for the vegetation of a given area of land, the source of a considerable propor-
tion of which is as yet not satisfactorily explained. The question whether or not the
assimilation of free Nitrogen by plants may account for all, or a part, of the otherwise
unexplained fixation, is seen to be left in a dilemma almost inexplicable, by the conflict-
ing character of the results that have been recorded relating to it. Yet, as has been
already said, upon the decision finally come to in regard to this question, must materially
depend the degree of importance to be attached to the investigation of the other actual
or possible sources of Nitrogen to plants, which we have briefly noticed. Under these
circumstances, it seemed desirable that any opinions we might offer or adopt on this
subject should have the support of such evidence as might be afforded by renewed expe-
riment. We proceed, then, to follow up our account of the Nitrogen-statistics of vege-
table production, the consideration of the several possible sources of Nitrogen to plants,
and the review of the results and opinions of others on some of the points at issue, by a
statement of our own experimental evidence in regard to this important question.

PART SECOND.

EXPERIMENTAL RESULTS OBTAINED AT ROTHAMSTED DURING THE
YEARS 1857, 1858, AND 1859.

Introductory observations.

In laying this part of the subject before the Fellows of the Royal Society, we shall
follow the general order in which the questions involved were presented to ourselves in
the investigation. In so doing it will be necessary :—

1. To consider all possible conditions to be fulfilled in order to effect the solution of
the main question of the assimilation of free Nitrogen by plants, and to endeavour to
eliminate all sources of error in our investigation.

2. To examine a number of collateral questions, which have a bearing upon the points
at issue, and to endeavour so far to solve them as to reduce the general solution to that
of a single question to be answered by a final set of experiments.

3. To give the results of the final experiments themselves, and to discuss their bear-
ings upon the question which it is proposed to solve by them.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 469

We shall dwell more fully upon the conditions involved in the experiments than
upon the numerical results which they have afforded, since the value of these results is
so wholly dependent on those conditions, that, if the latter are properly arranged and
thoroughly considered, any conclusion with regard to the former will be sufficiently
apparent from the numerical results themselves.

In studying the conditions, we shall be obliged to touch upon several collateral
points, embracing some questions not necessarily involved in the investigation, and
which, therefore, we have not attempted to treat with that fulness which, as distinct
questions in vegetable Physiology, they merit. Yet, we think, it will appear that, in
the degree in which we have followed them, their discussion is essential to complete
the consideration of the main question of the investigation, and that, in relation to it,
they possess an interest quite commensurate with the attention we have devoted to them.

These questions are embraced in the following :—

1. The preparation of the soil or matrix for the reception of the plant, and of the
nutriment to be supplied to it.

2. The preparation of the nutriment to be supplied to the plant,—embracing that of
mineral constituents (as in the ash), of certain solutions, and of water.

3. The conditions of the atmosphere to be supplied to the plant, together with the
means of securing them,—involving a consideration of the circumstances affecting the
composition of the atmosphere, and of the apparatus used to supply it.

4. The changes undergone by nitrogenous organic matter during its decomposition,
affecting the quantity of combined Nitrogen present, in circumstances more or less
analogous to those in which the plants were grown in our experiments upon the assi-
milation of Nitrogen.

5. The action of agents, as ozone, and the influence of other circumstances which may
affect the quantity of combined Nitrogen present in connexion with the plant, and yet
independent of the direct action of the vital (growing) process.

In considering these five questions, two important series of conditions must be
fulfilled :—

1. Those that relate to the growth of the plant,—which must be so arranged as to
include all that is necessary for healthy and vigorous growth, excepting only, in some
instances, such conditions as may depend upon the presence of a supply of combined
Nitrogen.

2. Those that relate to our means of measuring the quantity of combined Nitrogen
present at different periods of growth,—it being essential that we should be able, with
the means of investigation afforded in the present state of science, to ascertain the
quantity of combined Nitrogen present with the plant at different periods of its growth,
with sufficient exactness to detect any changes that may take place, so as to enable us to
refer them to their proper source.

If we succeed in fulfilling all these conditions, we shall have at our command all
the data requisite for the solution of the question whether plants assimilate free

470 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

Nitrogen. Our preliminary investigations will have enabled us to avoid, or to elimi-
nate, all sources of error due to the incidental circumstances of the research; and the
numerical results of a final series of experiments, showing the quantities of combined
Nitrogen supplied, and those eventually found in connexion with the plant, will afford
the necessary data for the solution desired.

In discussing the conditions involved in the experiments, and the researches under-
taken to enable us to estimate the value of those conditions, we shall arrange the sub-
ject in such order as will most clearly bring out their bearings upon the main question,
rather than according to the ofder as to time in which they were made. Several colla-
teral experiments were made, to prove that our conditions of growth, provided in soil,
atmosphere, and nutriment, were such as we had assumed them to be; for had they not
been so, the object of the investigation could not be attained. ‘The time required for
the conduct of these collateral experiments, made it necessary that many of them should
be performed simultaneously with the investigations the proper conditions of which
they were designed to make known.

We shall first consider the arrangement of the main experiments, and the plan and
results of the collateral inquiries with a view to show what the conditions of the former
should be, and then show how far the conditions assumed for the first year’s experi-
ments, and those arranged in the second year, after the results of some of the collateral
investigations were known, agree with the conditions indicated by the results of all the
collateral investigations taken together.

Section I—CONDITIONS REQUIRED, AND PLAN ADOPTED, IN EXPERIMENTS ON
THE QUESTION OF THE ASSIMILATION OF FREE NITROGEN BY PLANTS.

A.—Preparation of the Soil, or matrix, for the reception of the plant, and
of the nutriment to be supplied to tt.

In considering the subject of the soil to be used, the remarks made above on the
necessity of combining the conditions of healthy growth with the simplicity of constitu-
tion which would allow of a quantitative estimation of the results obtained, acquire a
high degree of importance.

So complicated is the constitution of ordinary soils, and so intimately are the nitro-
genous compounds existing within them associated with the other matters, that it is
impossible either to estimate the Nitrogen with suflicient accuracy for our present pur-
pose, or to extract it from the soil without entirely destroying the other conditions of
vegetable growth. We are, moreover, so entirely ignorant of the character of the
organic constituents of soils, of the state in which the principal part of the Nitrogen
exists in them, of the changes to which it is subject during vegetable growth and
decay, and, more especially, of its relations to vegetable growth, that an ordinary soil
could not possibly be used for our purpose.

Our ignorance of the actual constitution of soils, as regards the state of the organic

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 471

matter in them, and its relations to the inorganic substances, entirely precludes the possi-
bility of our imitating, by artificial means, a natural soil, so as to include all its condi-
tions excepting a supply of combined Nitrogen.

It is evident, therefore, that if all the conditions embraced in an ordinary soil were
essential to vegetable growth, the solution of the question of the assimilation of free
Nitrogen by plants would involve difficulties which our means of investigation in the
present state of science could not overcome. But the experiments to which attention
has been directed in the history of this subject, as well as others, the details of which
we shall give further on, show that such is not the case. They show that many of the
complicated conditions of an ordinary soil may be entirely dispensed with, so as to bring
the examination of it within our means of investigation, and yet to retain all the condi-
tions of healthy growth.

In the experiments of the first year, 1857, two kinds of soil, or matrix, were used.

One was prepared from an ordinary soil, so as more nearly to imitate the usual con-
ditions of vegetable growth. The other was prepared from volcanic pumice, with the
view to eliminate certain supposed sources of error which the prepared soil might intro-
duce. It was found, however, in the experiments of 1857, that there was no necessity
for this difference of matrix, and hence, in the experiments of 1858, only prepared soil
was used.

The soil selected for the preparation of the matrix was a somewhat heavy one (clayey),
resting upon chalk, and interspersed with flints. The large stones were removed by
picking and sifting; and the clayey lumps were powdered to prevent them from baking
into hard nodules during ignition. An attempt to ignite in ordinary clay crucibles was
not successful, owing to the reduction of the peroxide of iron to the state of black oxide,
and to the formation of sulphides from the reduction of the sulphates present, as indicated
by the vapours of sulphurous acid emitted during the ignition, and by the evolution of
sulphide of hydrogen on the addition of an acid to the mass after cooling.

The combustion proceeded satisfactorily in a large cast-iron muffle, through which a
constant current of air could pass. The ignition was continued until a portion of the
soil assumed, on cooling, the red colour due to peroxide of iron, and exhibited no trace
of coaly matter. The mass thus prepared was taken from the muffle, and thrown into
a large vessel filled with distilled water. .The water was rendered highly alkaline by
the quantity of caustic lime present. The fluid was decanted, and fresh portions of
water added several times during eight or ten days, until all the soluble matter was
removed. ‘The residue was then dried, and retained for final ignition before being used.
The ferruginous and aluminous character of this soil-matrix pointed to the danger there
might be of its acting as a porous body, to promote the formation of nitrogenous com-
pounds independently of vegetable growth, on the one hand, or to absorb and retain the
ammonia given to the plant, or that which might be formed from the nitrogenous matter
of the seed, on the other.

To ascertain the value of any influence exerted by the soil independently of the plant,
MDCCCLXI. 3T

472 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

in the manner just indicated, a pot of soil, prepared exactly as for an experiment with a
plant, was submitted to the same conditions of air, temperature, moisture, &c., as the pots
containing the experimental plants. The result was, that there was no accumulation of
combined Nitrogen. ‘The result with the matrix of pumice also showed, compared with
that of the soil-matrix, that no error was to be feared from the influence of the latter in
absorbing and retaining combined Nitrogen already in connexion with the plant.

For our purpose, pure volcanic pumice was used. It was powdered until the mass was
quite fine and the largest pieces were about the size of peas. ‘This powder was subjected
to long washing in the same manner as the ignited soil. Lastly, it was dried ready for
a final ignition before being used.

B.—The Mineral Constituents added to the prepared Soil.

In most cases the necessary Mineral Constituents were supplied in the form of the
ash of the plant of the description to be grown. In a few instances, where this was
not practicable, the ash of some other plant was selected. Weak solutions of sulphates
and phosphates, as well as ash, were also sometimes used.

In some instances the ash was obtained by burning a quantity of the entire plant
when in seed. In other cases, the seed and the rest of the plant being burnt separately,
a mixture of the two ashes was made in such proportion as to represent the composition
of the ash of the entire plant.

Thus, in the experiments of 1857, for Wheat a mixture of one part of the grain-ash
and six parts of the straw-ash, for the Barley a mixture of one part of the grain-ash
and three parts of the straw-ash, and for Beans a mixture of one part of the corn-ash
and two parts of the straw-ash was used. In the experiments of 1858, the ash used for
these crops was obtained by burning the entire plant. For Clover, the ash of Clover-
hay was employed.

In some instances of Leguminous plants the ash was saturated with sulphuric acid,
and then ignited, before being used.

Each ash was burnt in a large shallow platinum dish, heated in a current of air, in
a cast-iron muffle. The burning was continued until all coaly matter had disappeared.
The ash was then preserved, but was always submitted to a final ignition before being
used. Examination failed to detect combined Nitrogen in any of the ashes so prepared.

In order that the roots of the plants should find an abundance of mineral matter at
the most active period of growth, it was desirable that the matrix should contain as
much of such matter as was consistent with healthy development. A consideration of
the chemical constitution of soils suggested a proportion of 0-8 to 1:0 per cent. of ash;
and this was the quantity added to the matrix for the experiments of 1857; but for
those of 1858 only about half as much was employed.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 473

C.—The Distilled Water.

The first two-fifths of the distillate from ordinary water was allowed to escape, and the
next two-fifths were collected for further treatment. The water so obtained retained
traces of ammonia. It was mixed with phosphoric acid, free from nitric acid and
ammonia, in such quantity that the amount of acid present exceeded that of the ammonia
several thousand times. It was then re-distilled from a copper vessel to which was
attached a large Liebig’s condenser.

Under these circumstances no ammonia could go over unless it were carried over
mechanically, in which case it would be accompanied with several thousand times its
own weight of phosphoric acid; and, as no distilled water was used that gave any
evidence of the presence of this acid, the amount of ammonia in it, if any, must have
been several thousand times less than that to which the term “ traces”’ is applied.

The distilled water was so prepared only a few days prior to being required for
use.

All parts of the apparatus, the presence of ammonia in which could possibly affect the
result, were, after thorough washing both with ordinary and with common distilled
water, finally well rinsed with this pure double-distilled water just before being used.

D.—The Pots used to receive the Soil, Ash, Plant, &c.

For the experiments of 1857 common flower-pots were used; their height, and
diameter at the top, were each 6 inches, and their diameter at the bottom 5:2 inches;
their weight was about 1 lb. Small common white glazed earthenware plates were used
as the pans.

Subsequent observation suggested, for the experiments of 1858, the kind of pot, and
pan beneath it, represented in Plate XII. figs. 1, 2 & 3.

The Pot, of which fig. 2, Plate XII., represents the elevation, was made of the same
material as ordinary flower-pots. It was, however, made as light as possible, and was
not baked so hard as the latter generally are. The height, and diameter at the top,
were each 5 inches; and the diameter at the bottom was 4 inches. The bottom is per-
forated with about twenty holes of nearly one-fourth of an inch diameter, as is shown
in figs. 1 & 2. There were also two rows of similar holes (A, B, fig. 2) round the sides
at a distance of 0°5 to 1 inch from the bottom.

The Pan, represented with the pot placed in it in fig. 3, Plate XII., is made of hard-
baked and well-glazed stone-ware. It is 15 inch deep and 5:2 inches in diameter at the
bottom. At the top it is curved inwards (A, B, fig. 3), so as to adapt its upper rim to
the sides of the pot.

These arrangements of pot and pan afford several advantages, for the purposes of the
investigation, over those adopted in 1857. The surface for evaporation is less in pro-
portion to the volume of soil. The facilities for the exit of roots, and for the access of
air, are, on the other hand, greater. The pan affords room for an abundance of water,

372

474 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

in which the roots develope luxuriantly*. Yet this water does not evaporate so freely
as it otherwise would do, owing to the inward curve of the top of the pan, which also
serves to protect the roots distributed through the water from the direct action of sunlight.
All the conditions of growth are thus attained with a minimum of evaporation from all
sources excepting through the plant itself; and a drier atmosphere is maintained. Con-
sequently evaporation through the plant is favoured, and hence the conditions are pro-
vided for a constant supply to the plant of all the mineral and gaseous substances in
solution in the fluid of the soil and pan.

E.—Final preparation of the Soil, Ash, and Pot, for the Plant.

The soil and ash, each prepared as described in the foregoing subsections, and the
pot, also as described above, were simultaneously heated to redness; and the soil and
ash, whilst red-hot, were mixed together in the red-hot pot, which was placed upon a
red-hot brick over sulphuric acid. ‘The pot and contents were then covered with a large
glass shade, and left to cool.

The soil, as in its former preparation, was heated in a cast-iron muffle, from which it
was removed with a small iron shovel adapted to the purpose, and heated to redness
before being used.

Four or five pots were heated together, one inside the other, the top and bottom ones
of which almost invariably broke, either on the application of the heat, or on remoyal
from the fire; so that only about half of those operated upon were finally available for
use.

From 23 lbs. to 3 lbs. of ignited soil were put into each pot; but in the experiments
of the second year, 1858, the lower part of the pot was first filled, to the depth of about
1 inch, with very coarsely broken-up red-hot flint. In 1857, about 14 grammes of ash,
and in 1858 about 7 grammes only, were used for each pot. The greater portion of the
ash was mixed with the lower layers of the soil; but some was distributed through the
whole of it.

After cooling down sufficiently, the shade was removed, and about 500 cub. centims.
of distilled water, prepared as described in subsection C, were added to the soil of each
pot, this being as much as it would absorb. Then, after a lapse of ten to twenty hours,
the seeds or plants were put in.

F.—The Seeds and Plants taken for experiment.

In all the experiments recorded, the plants were grown directly from seed sown in the
soils prepared as above described.

In every case, seed of the best quality was taken, which was kindly presented to us
for our purpose by the Messrs. THomas Gisss and Co., of Half-Moon Street, Piccadilly,

* See Table, and general remarks at p. 524; also notes of root-development of Wheat No. 6 (1857), p. 553,
Wheat No. 1 (1858), p. 560, and Wheat No. 9 (1858), p. 569.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 475

Seedsmen to the Royal Agricultural Society of England, who bestowed much labour
and attention upon the selection. From the quantity of each kind received, the largest
and the smallest were picked out, as were also any that did not look quite healthy.
Given numbers of the remainder were then weighed, and the average weight, per seed,
was calculated. A few seeds, each weighing as nearly as possible the mean weight, were
then selected for planting.

In order to estimate the quantity of Nitrogen in the seeds sown, in some cases a quan-
tity of seeds equal in weight and number to those sown was submitted to analysis. But
the difficulties of grinding, without loss, so small a quantity, and the consideration that
one small quantity might differ more in composition from another such quantity, than
either would from the average composition of a large number of well-selected seeds, led
us generally to estimate the Nitrogen in the seeds sown from the percentage of it found
in the mixture of a large number ground up together.

The seeds selected for growing were sown in the pots of soil prepared as already
described, to the depth of about 1 inch below the surface. With large seeds, such as
Beans, it was necessary that care should be taken so to deposit them that the radicle
and plumule should each take its natural direction. If this precaution was neglected,
the seed was liable to be raised out of the soil after sprouting, which involved the incon-
venience of opening the apparatus in which the plant was enclosed, in order to re-bury
the seed.

In some cases, as soon as the seeds were sown the pots were removed from over the
sulphuric acid, and placed at once beneath the large glass shades which were to serve as
the enclosing apparatus. In other instances, the pots were first placed under other
shades, luted by mercury or sulphuric acid, and standing in the laboratory, and then,
after a few days, they were removed to their final position.

G.—The Atmosphere supplied to the Plants.

As regards the essential conditions of growth, and the circumstances associated with
it, which must be kept within the control of our means of investigation, the same
remarks apply to the atmosphere, though with less force, as have already been made in
reference to the soil (subsection A, p. 470).

It is true that the constitution of the atmosphere is less complicated, and that we are
much better acquainted with it than we are with that of ordinary soils; yet the extreme
mobility of the atmosphere renders the presence in it of exceedingly small quantities
of substances calculated to influence vegetable growth much more dangerous in quan-
titative experiments on vegetation than would be their presence in the soil. Thus the
presence of gaseous impurities, and of solids mechanically suspended, in the atmosphere
cannot be overlooked. And hence, although it is not necessary to submit the natural
atmosphere to such radical changes as those to which the natural soil must be subjected,
some measures must be taken to exclude the sources of error to which allusion has just
been made.

476 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

As in the case of the soil, so in that of the atmosphere, the only essential conditions
to be attained are such as are required for healthy growth, and as will at the same time
enable us to estimate the amount and the sources of the combined Nitrogen coming
within the reach of the plant by its means.

In consequence of the mobility of the atmosphere above referred to, it was necessary
to exclude the experimental plants from its free access. The quantity of ammonia in
the air is, however, so very small, that, provided the atmosphere of the enclosing apparatus
were allowed to remain unchanged throughout the period of an experiment, the amount
of combined Nitrogen so coming within the reach of the plant might be altogether
neglected. Nor, so far as regards the nitrogen and oxygen of the air, is there any
necessity for change; but, owing to the peculiar circumstances of temperature and of
moisture to which the air of the apparatus is subjected, conditions more closely allied
to those of ordinary vegetation are attained by a frequent change of atmosphere. ‘The
large quantity of air which thus becomes involved in an experiment precluded the idea
of neglecting the consideration of the combined Nitrogen which it contains. It devolved
upon us, therefore, either to determine the total amount of combined Nitrogen in the
air before and after it came in contact with the plant, or to free the air from combined
Nitrogen before admission into the enclosing apparatus. The latter alternative was
adopted as the most simple; and the manner in which the object was effected will appear
from the following description of the apparatus employed.

H.—The Apparatus used to enclose the Plants, and to supply them with Air, Water,
Carbonic Acid, &e.

Plate XIII. represents the entire apparatus as used for each separate experiment in
1857; and fig. 1, Plate XIV., that used, also for each separate experiment, in 1858, in
which, as will be seen, several important modifications of the arrangement adopted in
1857 were made.

The same letters of reference apply to the two so far as the parts are alike; and
where there has been any modification in the arrangement in 1858, as compared with
that in 1857, the same letters represent the parts of the apparatus used for the same
purpose in each, with the exception, that those which apply to the modification of the
apparatus in 1858, are distinguished by a dash, thus '.

A, Plate XIII. (and fig. 1, Plate XIV.), represents a large stone-ware Woulfe’s bottle,
18 inches in diameter and 24 inches high.

B, C, and E are glass Woulfe’s bottles of 30 ounces capacity.

F is a large glass shade, the dimensions of which were, in most of the experiments,
diameter 9 inches, and height 40 inches; in other cases the dimensions were, diameter
16 inches, and height 28 inches.

a represents the cross section of a ect pipe 14 inch in diameter, which is in con-
nexion with a reservoir of water, not shown. ‘This pipe passes over all the vessels A (of

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 477

which there is one included in the apparatus for each separate experiment) in a direction
at right angles to the plan of the figure. It is connected with each vessel A by means
of a tube a, in which is fixed a stopcock, to open and shut the connexion between the
water-supply tube @ and the vessel A.

ede, Plate XIIL., isaleaden exit-tube forair. cd’ é, fig. 1, Plate XIV., is the corre-
sponding tube in the apparatus of 1858, which is enlarged at the point ¢ and downwards
until it opens into the vessel A, thus allowing another, g'7’s', to pass through it and
down to the bottom of the vessel A, as indicated by the dotted line. This tube g'7"s! is
a half-inch safety-tube, opening externally at g', and in the apparatus of 1858 replaces
the tube g 7 s shown in Plate XIII.

The bottles B and C are filled to the depth of 23 inches with sulphuric acid of
sp. gr. 1°85.

The tube D D is about 3 feet long and about 1 inch in diameter, and is filled with
fragments of pumice saturated with sulphuric acid. At f,f, in this tube, are small
indentations to prevent the sulphuric acid from draining against the corks.

The Woulfe’s bottle E contains a saturated solution of ignited carbonate of soda.

gh is a bent and caoutchouc-jointed glass tube, connecting the interior of the
Woulfe’s bottle E with that of the large glass shade F.

ik, better indicated in fig. 2, Plate XIV., is the exit-tube for the air, connecting
the interior of the shade F with an eight-bulbed apparatus M, containing sulphuric
acid.

ww, Plate XIII., is a block of slate 12 inches square and 3} inches thick, in which is
a circular groove, half an inch wide and 2 inches deep, adapted to the diameter (9 inches)
of the glass shade F, the bottom of which rests in it. The groove is filled with quick-
silver, which shuts off the communication of the external air with the interior of the
shade. It is widened and deepened at four equidistant points, to admit of glass tubes
passing underneath the shade. Two of these tubes, gh and 0, are shown in Plate XIII,
and gh also in fig. 1, Plate XIV., no being there replaced by n'o'. The other two
are at right angles to these, and are best seen in the vertical section of the shade and
lute, fig. 2, Plate XIV., lettered wv and t& respectively. The tube wv is for the
supply of water to the plant; and the tube 7# is for the exit of the air, from which
it passes outwards through the sulphuric acid in the eight-bulb apparatus M. This
vertical section of the shade and lute is at right angles to the view of them in fig. L.,
Plate XIV.; and from it a judgment may be formed of that of the shade and lute of
Plate XIII, as well as of the corresponding tubes to those last described, in the appa-
ratus of 1857.

The tube xo, Plate XII, passing from the outside, beneath the shade, and extending
to the surface of the mercury in the groove within the shade, is for the purpose of
withdrawing condensed water. In the apparatus for 1858, the arrangement for this
object is rather different. Thus O, fig. 1 (and fig. 2), Plate XIV., is a bottle into which
passes a tube m0’, opening into the bottom of the lute w'w' by means of a hole at 7’,

478 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

seen better in figs. 4 & 5, Plate XII., which represent, respectively, the plan and the
vertical section of the glazed stone-ware lute-vessel used in 1858. Another glass tube (¢’)
passes to the bottom of the vessel O (figs. 1 & 2, Plate XIV.), for the purpose of with-
drawing the condensed water which collects in it.

The plan of the stone-ware lute-vessel used in 1 858 (fig. 4, Plate XIT.) shows the groove
for the mercury, the four widened and deepened points of it for the passage of the tubes
under the shade (of which however three only were used), and the hole 7’ at the bottom,
for the reception of the tube for carrying off the condensed water. ‘This lute-vessel is
made of hard-baked and well-glazed stone-ware, and is, in fact, simply a shallow dish
with double concentric sides, the space between which latter forms the groove for the
reception of the shade and of the mercury luting, and for the passage of the tubes.
Figure 5, Plate XII., is a vertical section of the stone-ware lute-vessel, from A to B,
fig. 4, through two of the widened and deepened portions of the groove, and through
the hole n'. Figure 6, Plate XIL., is also a vertical section of the lute-vessel, but from
C to D, fig. 4.

The Woulfe’s bottle T, fig. 1, Plate XTII., and T’, fig. 1, Plate XIV., is for the supply
of carbonic acid, and will be referred to, more fully, in the following subsection I.

I.— Use of the Apparatus.

If the stopcock below a (fig. 1, Plate XTII., and fig. 1, Plate XIV.) is opened, water
flows into the vessel A from a large reservoir with which the leaden tube @ is in con-
nexion. As the pressure increases, the water rises in the safety tube g7s, or 77's,
above the level in the vessel A, and at the same time the air begins to escape by the
tube cde, or cd’ ée’, to force its way through the sulphuric acid in the bottles B, C, then
to traverse the tube D D, containing the pumice saturated with sulphuric acid, to
bubble through the solution of carbonate of soda in E, and finally to enter the shade F
by the bent and jointed tubes g, h; and from the shade it passes out through the tube
ik and the bulb-apparatus M containing sulphuric acid, into the external air.

The minimum pressure required to produce this passage of air, expressed in the
height of a column of mercury which it would sustain, is equal to the sum of the pro-
ducts obtained by multiplying the height of each fluid through which the air has to
pass by the sp. gr. of the same, divided by the sp. gr. of mercury, or

[(2°5+2:5-+1-0) 1:85 4-2'5 X1-2];4g=1-037 inch,

in which 1-2 is the sp. gr. of the carbonate-of-soda solution.

The difference between the height of the water in the vessel A and in the safety-tube
qr's, or qr’ s', must always be equal to the weight of the mercury column obtained in
the manner just indicated, multiplied by the sp. gr. of mercury.

If the difference between the height of the highest points of the tubes g7's and ede,
fig. 1, Plate XIII. (that of the former being the higher), be less than the minimum height

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 479

just referred to, then the water must flow out of A through the safety tube g, 7, s before
it can pass through the tube ¢, d, e, into the bottle B. In accordance with this con-
sideration, the safety-tubes for the apparatus of 1857 were arranged as shown in
Plate XIII. (g, 7, s); but, owing to occasional leakage of the joints at the top of the
vessel A, this principle could not be relied upon; and hence the arrangement shown in
fig. 1, Plate XIV. was adopted in the experiments of 1858.

The height from the top of the vessel A to 2” (fig. 1, Plate XIV.) was 12 inches, which
is sufficient to allow the whole of the air to pass out of the vessel A, whilst the great
height of d', of the tube c, d’, e', entirely prevented the water from passing over into the
bottle B,—an accident which unfortunately happened on a few occasions with the appa-
ratus of 1857.

When the vessel A was full of water, it was drawn off by a cork-hole at the buttom,
air being at the same time admitted by the tube wv at the top of the vessel.

The minimum pressure upon the glass shade F would be

1:0 x 1°85

13°6
in which 1-0 is the difference between the height of the lowest and the highest level of
the sulphuric acid in the bulb-apparatus M. Experiments showed, however, that owing
to friction, &c., the maximum pressure on the inside of the glass shade would be raised

—— Oot Ommchs

to double the above estimated minimum.

The plants were supplied with water, as already said, through the tube wv, shown best
in fig. 2, Plate XIV. At first fresh distilled water was supplied; but as soon as a suffi-
cient quantity of condensed water had run through the tube wo’ and collected in the
bottle O, this was drawn off by means of the tube ¢ to water the plant when required.
In the experiments of 1857, the condensed water was drawn off from time to time, from
the surface of the slate and mercury, by means of the tube x 0.

All the Woulfe’s bottles were made as air-tight as possible by means of very good
corks. Those of the bottles E, Plate XIII., and fig. 1, Plate XIV., and also those of O,
fig. 1, Plate XIV., were, however, covered with a cement, composed of cight parts gutta
percha, twelve parts common rosin, and one part Venice turpentine, well melted toge-
ther. The glass tube n' 0’ was also fixed into the lute-vessel ww, at a’, with this
cement.

In the experiments of 1857, tubes of unvulcanized caoutchouc, made by ourselves
from the sheet, were used for the various joints indicated in the figures; but as these
soon became unsound under the influence of the atmospheric changes to which they
were exposed, tubes of vulcanized caoutchoue were substituted in 1858. The ends of
the glass tubes 0 and w, Plate XIII., and of the tubes ¢ and w, fig. 1, Plate XIV., were
fitted with pieces of caoutchouc tubing into which pieces of solid glass rod were fixed
as stoppers.

In 1857, twelve such sets of apparatus, and in 1858 a larger number, were employed.
The whole were arranged side by side, on stands of brickwork erected for the purpose,

MDCCCLXI. 3U

480 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

in the open air, and were protected from rain, or the too powerful rays of the sun, by a
canvas awning which could be drawn down over them, or withdrawn, at pleasure.

In 1858, in addition to the sets of apparatus above described, two glazed cages, such
as were used by M. G. Vite in his experiments, and which he kindly sent over to us
for the purpose, were employed.

J.—The supply of Carbonic Acid to the Plants.

Owing to the small proportion of carbonie acid in the atmosphere, and to the fact
that a part of it would be absorbed in passing through the apparatus just described, it
was necessary to give a supply of it to the plants artificially. It was obtained by the
action of chlorhydric acid upon fragments of marble in the vessel T, Plate XIIL, or T’,
fig. 1, Plate XIV.

In regulating the supply of carbonic acid, the points to be observed were, to keep the
proportion in the enclosed atmosphere below that in which it would prove injurious to
the plants, and at the same time to provide a sufficient quantity for the demands of
vegetation at the most active periods of growth.

Boussineautt found* that the air surrounding a plant might, consistently with
healthy growth, contain 8 per cent. of carbonic acid. This amount, then, on the one
hand, and the very small quantity in the atmosphere which is sufficient for natural
vegetation (about 0:04 per cent.), on the other hand, afford us limits between which a
wide range is allowed for variation.

Calculation showed that a minimum quantity of 0:2 per cent. of carbonic acid in the
air of the enclosing apparatus would supply 5 cubic inches of the gas within the shade
at one time, corresponding to 0:0439 gramme of carbon—a quantity which, maintained
daily throughout the sunlight, would be very much more than was required by the plants.

It is obvious, therefore, that a variation in the amount of carbonic acid in the atmo-
sphere of the plants between 4:0 per cent. and 0:2 per cent. would be very safely within
the limit suggested by the experiment of BousstnGauLt as the maximum, on the one
hand, and that indicated by the above considerations as the minimum desirable in the
experiment, on the other.

A question arises as to the influence which the changes in the proportion of carbonic
acid in the air, between the assumed limits, may have upon the plant. In reference to
this point, it may be mentioned that our own experiments upon the nature of the gas
in plants (some of the results of which will be given further on) appear to show that
the changes in the proportion of the carbonic acid in the air of the cells and intercellular
passages, and in that in the fluids of the stem, are much greater, and more rapid than
those which can take place in the atmosphere of our apparatus. In addition to this,
may be stated the fact that plants derive much of their carbonic acid from aqueous
solution absorbed by the roots; and most probably the remainder is absorbed by the
fluids of the plant before influencing its growth. These absorptions can take place but

* Mémoires de Chimie Agricole et de Physiologie, 1854, p. 441.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 481

slowly; so that somewhat rapid variations in the”proportion of carbonic acid in the
atmosphere surrounding the plant, will be accompanied by much less variation in the
proportion of carbonic acid within the plant. The latter will, therefore, be a slightly
varying mean between amounts corresponding to the foregoing extremes.

From the above considerations, it appeared probable that there would be no danger
in so supplying carbonic acid to the atmosphere of the plants as that its proportion
should reach its maximum in a short time, and then, by the passage of air, gradually fall
again to the minimum. A few trials, adding different quantities of chlorhydric acid to
the vessel T, Plate XIII. (or T’, fig. 1, Plate XIV.), containing marble, enabled us to
ascertain the proper quantity to add, to provide about 4 per cent. of carbonic acid in the
shade F when air was not passing. Then passing air, it was found that the proportion
of the gas was never reduced below that which we have above assumed as the proper
minimum. In practice a little more chlorhydric acid than the amount so determined
was used; and then the passage of the air was commenced simultaneously with the
addition of the acid. Repeated analysis of the air in the enclosing apparatus showed
that, operating in this way, our assumed limits for the maximum and minimum propor-
tions, respectively, of carbonic acid were not passed.

The volume of the air passed through the apparatus daily, was that of the vessel A,
Plate XIII. and fig. 1, Plate XIV., and was equal to about 2°5 times that of the
enclosing shade F.

K.—ddvantages of the Apparatus above described.

The advantages, for the purpose in question, of the plan of apparatus which has been
described, over those of several of the forms that have been suggested or used by others,
may be very briefly stated.

1. When once ready to receive the plant, the use of the apparatus is extremely simple
and easy. It is only necessary to place the pot containing the soil, seed, &c., with its
pan, in the stone-ware lute-vessel, to pour mercury into the groove, to arrange the several
tubes, and to put on the shade. ‘The plant is then entirely excluded from all external
sources of combined Nitrogen; and, in case of its being necessary to open the vessel
for any purpose, this can be done with great facility.

2. By means of the arrangement of the bottle O (fig. 1, Plate XIV.), the water which
condenses within the shade is removed from the atmosphere of the plant as soon as it
collects. The small pan in which the pot stands (fig. 3, Plate XIJ.), with its inward-
turned sides, allows of a store of water being kept beneath the plant which is at the
same time protected from free evaporation. ‘The vessel O holds as much water as can be
evaporated from the plant and soil during several days. The supply of water to the
plant is exceedingly easy and simple, it being only necessary to remove that which has
collected in the bottle O by means of the tube #, and to pour it in at w (figs. 1 and 2,
Plate XIV.). [In the arrangement for the experiments of 1857 the condensed water
collected on the surface of the slate, until removed by means of the tube 2 0. |

3U 2

482 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

3. A simple glass shade is liable to introduce fewer sources of error than a com-
plicated metallic framework with panes of glass cemented into it. ‘The shade is easier
to clean before commencing the experiment, and it is less likely to retain, at the termi-
nation of it, any of the combined Nitrogen, either derived from the plant, or from that
which has been supplied during growth. Lastly, the presence of oxidizable metallic sur-
faces, affording a possible quantity of nascent hydrogen which might form ammonia with
the Nitrogen of the air, is avoided.

4, There is no organic matter present which can affect the result of the experiment.
The only organic matter within the shade is that of a thin coating of the gutta-percha
cement which has been described, by which the tube 7 (fig. 1, Plate XIV.) is fixed into
the hole 7’ (fig. 4, Plate XII.) at the bottom of the stone-ware lute. On analysis this
cement was found to contain from 0°10 to 0°15 per cent. of Nitrogen. Hence, if the whole
quantity of the cement in contact with the condensed water became decomposed, aud
yielded up its Nitrogen in such a manner as to become a product of the experiment, it
would only so yield a few tenths of a milligramme of Nitrogen; but experiment proved
that it did not suffer sensible decomposition when subjected, during a whole year, to
exposure in the open air. :

5. In the passage of the air through the apparatus, the excess of pressure was upon
the inside, instead of, as in the experiments of others, upon the outside of the enclosing
vessel. In experiments of the kind in question in which the apparatus is exposed to
the open air, and so subjected to climatic vicissitudes during a considerable period of
time, the ordinary means of securing tightness in the laboratory cannot be depended
upon; and an apparatus proved to be tight at one time may, as the result of a variety
of causes beyond our control, be subject to leakage at another. But a leakage from the
inside of the apparatus outwards cannot affect the result of our experiment; whilst a
leakage in the opposite direction might introduce combined Nitrogen from the external
atmosphere. In the arrangement which has been described, the excess of pressure is
always on the inside during the passage of the air; and when the air is not passing
there cannot be any important amount in the opposite direction due to changes of tem-
perature and barometric condition, for it can never exceed that required to drive the air
inwards through the bulb-apparatus M (Plate XIII., and fig. 1, Plate XIV.), which is
altogether insignificant.

6. That part of the apparatus which would be the most lable to leak, and which
would be the most damaged by pressure, is subjected to the minimum amount of it.
The entire pressure required to force the air through the apparatus, independently of
that necessary to overcome friction, is

5 x 1:85=9-25 inches of water

to pass through the sulphuric acid in the bottles B and C (Plate XIII., and fig. 1, Plate
XIV.), and
2°09 X 1:2=3°6 inches of water

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 483

to pass through the solution of carbonate of soda in the bottle E, and
1x 1°85=1°85 inch of water

to pass through the sulphuric acid in the bulb-apparatus M, equal a total of 14:10 inches
water, or a minimum pressure of about 0:5 lb. per square inch. Direct experiment
with a manometer showed, however, that the entire pressure, minus that due to the sul-
phuric acid in the bulb-apparatus M, might, owing to friction, &c., amount to 0-8 Ib. per
square inch. ‘This would give a lateral pressure upon the sides of the glass shade of about
900 lbs., if the current of air were produced by aspiration instead of forcing—a condition
which would be incompatible with the safety of the vessel. In the mode of experiment-
ing adopted, however, the only pressure exerted upon the glass shade was the amount
requisite to force the air through the bulb-apparatus M.

It remains to consider the influence upon the air of its contact (in the vessel A) with
the water employed to force it through the apparatus. This can be of three kinds :—

1. The proportions of nitrogen and oxygen may be slightly affected by absorption,
under the influence of the slightly increased pressure to which the air is subjected.

2. The air may lose its carbonic acid.

3. It may become more or less saturated with aqueous vapour.

The increase of pressure to which the air is subjected in the vessel A is so slight, and
the time in which it is there in contact with the water is so short, that the total amount
of oxygen and nitrogen absorbed by the water must be very small; and, since any
change in the constitution of the total amount of air will be dependent on the ratio of
the absorption coefficients of oxygen and nitrogen on the one hand, and on the ratio of
the quantities of these gases in the air on the other, it will be very much less than in
the actual amount of air absorbed; it will in fact be too small to be of any importance.

The whole of the carbonic acid of the air may be absorbed by the water; but as
arrangements are made for the artifical supply of it, this is of no consequence.

The amount of water taken up by the air in the vessel A would at first sight appear
to be of more importance. But the time during which the air is in contact with the
water in the vessel A is very short, and probably too short for its saturation; it must
lose most or all of its acquired water in passing through the sulphuric acid in the bottles
B and C, and over the pumice saturated with sulphuric acid in the tube DD, whilst the
redried air passes too rapidly through the carbonate of soda solution in the bottle E for
re-saturation ; and lastly, as the air in its previous course through the apparatus will be
cooler than within the shade, it will not be so near its point of saturation in the latter as
it may be before it reaches it.

L.—Adaptation for healthy growth of the conditions of experiment adopted.

We have thus far discussed the possible sources of error in an experiment on the
question of the assmilation of Nitrogen by plants, so far as regards the soil, the inorganic
nutriment, and the air, to be provided for the plant, and we have pointed out the means

484 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

adopted to avoid them. From known considerations with regard to the requirements in
the soil and inorganic nutriment on the one hand, and in the atmosphere of the plants
on the other, and in all combined, we have concluded what are the proper conditions of
vegetable growth. It remains, however, to appeal to the results of direct experiment, to
show that our adopted conditions possess the value which we have assumed them to have.

A pot of good garden soil, capable of supporting luxuriant vegetation in the open air,
was sown with Wheat, Barley, and Beans, and then placed under one of the experimental
shades, and submitted to exactly the same atmospheric conditions as those provided in
the experiments on the assimilation of Nitrogen. The result was, exceedingly luxuriant
growth (see Records of growth in Appendix, Experiment No. 12, of “ Plants grown in
1857,” fig. 18, Plate XV.; and also Experiment No. 15, of “Plants grown in 1858.”
It was thus proved that the aérial conditions supplied in our experiments were adapted
for healthy growth.

When pots of soil, prepared precisely as has been described above, were sown with seed
and combined Nitrogen artificially supplied, vigorous growth was the result. Hence it
was shown that the conditions of soil were properly selected.

Section II.—OTHER CONDITIONS OF EXPERIMENT, REQUIRING COLLATERAL
INVESTIGATION.

There remain to be considered several conditions which might affect the result of a
quantitative experiment on the assimilation of Nitrogen by plants, dependent upon the
reciprocal action of the air and the soil, with or without the connexion of the plant.

The following conditions possibly affecting the result of such an experiment, due to the
mutual action of the soil, air, and organic matter of the plant, require to be considered :—

1. The influence of ozone, either within the cells of the plant, or in connexion with
it, in promoting the formation of nitrogenous compounds from free Nitrogen. The
influence of ozone in promoting such formation within the soil, either directly, or in con-
nexion with the organic matter of the plant.

2. The decomposition of nitrogenous organic matter, in relation to the question
whether there be an evolution of free Nitrogen in the process.

3. The formation of nitrogenous compounds, through the mutual action of nascent
hydrogen evolved by decomposing organic matter, and free Nitrogen.

A.—General considerations in regard to the possible influence of Ozone on the
supply of combined Nitrogen to growing plants.

The consideration of Ozone in connexion with the plant suggests the possibility of its
presence in two distinct ways. It may occur within the cells and intercellular passages
of the plant, either in the gaseous state or in solution, or it may be simply around the
plant, without existing within its structures.

With regard to the origin of Ozone in connexion with the plant, it may be a product

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 485

of the action of the sun’s rays, by virtue of which carbonic acid is decomposed, and
oxygen evolved. Or, it may result from other causes, to which we shall refer pre-
sently.

In order to ascertain how far the presence of Ozone within the plant may have a
bearing upon the point at issue, we have attempted to solve, by experiment, the follow-
ing questions :—

1. Is there, during the growth of plants, Ozone within the cells or intercellular pass-
ages?

2. If Ozone be present within the structures of the plant, is it in circumstances in
which it would be likely to oxidize free Nitrogen into any of its oxygen compounds ?

3. Is Nitric acid present in the living cells of any plant of which it is not a natural
product of growth?

In a number of experiments which we have made upon the gases obtained by exhaust-
ing plants placed in water freed from air by boiling, no Ozone was perceptible. An-
other series of experiments upon the oxygen evolved from plants immersed in water
saturated with carbonic acid gave similar results.

In the latter series about 1 ounce of the green plant was placed in 500 cub. cents. of
carbonated water, and the whole subjected to sunlight. The decomposition of carbonic
acid commenced almost immediately, and the evolution of gas was rapid. In this way
100-200 cub. centims. of gas were obtained, which contained sufficient oxygen to inflame
a glowing taper; yet no trace of Ozone was manifested on placing test-paper in the gas.
That evolved from Wheat, Barley, Oats, Beans, and Clover behaved alike in this
respect. Granting that these experiments may not be conclusive for all conditions of
the decomposition of carbonic acid by plants, that under certain circumstances Ozone
may exist within the vegetable cells and the passages between them, and that it is pos-
sible that some of the oxygen of the decomposed carbonic acid may at times appear as
Ozone, still, it is difficult to see how it can exert any oxidizing influence upon the free
Nitrogen within the plant, under the peculiar circumstances in which it must come in
contact with it.

In order to study more fully the circumstances, and to examine, in some detail, the
value of the oxidizing and reducing forces operating in the vegetable organism, in the
different conditions to which it is subjected during growth, a number of experiments
have been made upon plants, under a variety of conditions more or less analogous to
those of ordinary growth. As the results of these investigations are too extended in their
bearings for full consideration in the present Paper, and are, moreover, not yet sufficiently
complete for publication, we shall give here only such of them as bear upon the point
now in question.

It is obvious that the formation of Nitric acid, by the mutual action of Ozone and
free Nitrogen within the plant, will be dependent upon the activity of the oxidizing
power of the Ozone, and on the intensity of the reducing power of other substances in
contact with the Nitrogen to be oxidized.

486 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

The investigations of ScuénperN and others appear to show that, under certain cir-
cumstances, nitric acid may be formed by the mutual action of Ozone and free Nitrogen.
The question for our consideration here is, whether these circumstances are presented
in the cells of plants, and in the passages between them, during growth? The subject of
the relation of Ozone to organic matter is obviously too extensive for anything more
than a passing consideration here; but we may refer to the well-known intense action
of this peculiar body upon organic matter generally, by which carbonic acid is formed,
and the Ozone destroyed. It is well known that Ozone is rapidly destroyed if kept in
contact with phosphorus or any other reducing substance. If such conditions for the
destruction of Ozone exist within the plant, the probability that it can there oxidate free
Nitrogen, and so form nitrates, would appear to be exceedingly small. The actual con-
ditions within the plant in regard to the points in question may be most efficiently
studied by the examination of the gases they contain, under various circumstances. We
proceed, therefore, to notice some of the results of such an examination.

B.—Composition of the Gas in Plants.

Experiments, Series 1.

Plants, or parts of plants, were put into a flask filled with water that had previously
been well boiled to remove all air from it. A cork, through which a bent glass tube was
passed, was then pressed into the flask, so that the tube was filled with the displaced
water. The flask was then placed over a lamp, the water boiled, and the water and gas
driven over collected over mercury, the boiling being continued until the water distilled
over raised that first driven out with the gas to the boiling-point. The vapour thus
produced expelled most of the water collected over the mercury. In this way the gas
driven out from the plant at the boiling-point was obtained. ‘The following Table (1.)
shows the composition of the gas collected under these circumstances. It is seen that
Nitrogen and Carbonic acid only were present.

Taste IL—Showing the Percentage Composition of the Gas evolved from plants,
in water, on continued boiling.

Description of plant operated upon. Per cent. |
Date } ay
(1857). Plant. Part of plant. How manured, &e. | Nitrogen. | Oxygen. pia |
May 6. | Wheat. | Whole plant. |Mineral manure ......cccseseeeeeeeeeeeeees, 45°47 0-0 54°53 |
May 2. | Wheat. | Whole plant. |Mineral manure .........sceseeeeeeeeeeeees || 46:29 0-0 53°71 |
May 2. | Wheat. | Lower part. |Mineral manure .............e0-e+seseeeeee | 57°00 0-0 43°00 |
May 2. | Wheat. | Whole plant. |Mineral and Ammoniacal manure...... || 39:14 0-0 60°86 |
May 2. | Wheat. | Upper part. |Mineral and Ammoniacal manure...... | 37°53 0-0 62°47
| }
May 6. | Bean. | Whole plant. |Mineral manure ikea See ee 62°79 0-0 37°21 |
May 6. | Bean. | Whole plant. |Mineral manure eS gs Mage | 63-80 oo | 36-20

Other experiments gave similar results, all tending to show that the reducing power

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 487

of the vegetable cells, dependent on the character and conditions of the carbon com-
pounds they contain, was sufficient, under the circumstances specified, to consume all
the oxygen (or ozone) that might be present. But the high temperature at which the
experiment was conducted must have tended very much to increase this action. In
subsequent experiments a different plan of operation was adopted, not open to the same
objection.

Experiments, Series 2.

In these experiments, as in all those subsequently referred to, the plants were put into
a tall glass vessel (fig. 7, Plate XII.) 1:75 inch in diameter, and 14 inches in height.
The mouth of this vessel is fitted with a long cork, previously well boiled in bees’-wax.
Through the cork, two glass tubes, @ and 6, are inserted. The vessel being filled with
water well boiled and then cooled without access of air, the plant is put in and well
shaken to remove adherent air-bubbles. The cork, with its two tubes, is then forced
in, taking care that both the tubes become filled with water and that no air remains
in the vessel. As a further security for tightness, a piece of wide and thick caoutchouc
tubing may be drawn over the neck of the vessel, projecting upwards a little above the
cork, and then the cup thus formed partly filled with melted wax, forming a layer over
the cork and its joints. A funnel is then attached to the tube 5, by means of a caout-
chouc tube which can be closed by a strong pinch-cock. Water being admitted through
the funnel into the tube 6, the tube @ becomes filled, and it is then brought into con-
nexion, by means of a glass tube and caoutchouc joint fitted with a pinch-cock, with a
vessel filled with quicksilver. The connexion being opened, the quicksilver is allowed
to flow from the vessel by means of a long tube of more than barometric length fitted
into the lower part of it, thus forming a Torricellian vacuum in the mercury vessel. The
gas from the plant passes over into this vacuum, and bya simple arrangement is collected
in a eudiometer tube for examination.

The following Table shows the amount and composition of the gas obtained from
different plants, in the shade, in the manner above described.

MDCCCLXI. ox

485 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

TABLE I1.—Showing the amount and the composition of the Gas given off by
plants, in the shade, into a Torricellian vacuum.

1 | Per cent.
Description. | Total SEE
Gas | j

Date. | __ # ee _ | collected,|| ed || Oxygen
ee rT? cub. ||Nitrogen.| Oxygen. no ag Cc _ :
Part of Plant. How manured, &e. || cents. || | concn: pata 2

acid.

Wheat; 1858.

June 16.) Whole plant Mineral manure........-ss.ceseseeyeees 570 || 77°72 2:28 | 2000 | 22-28

June 17.) Whole plant ... ..|Mineral manure.......-0.2-2+-s2-+0++0- 553 77°94 5°06 | 17-00 22-06

June 16.) Whole plant ... ..|Mineral and Ammoniacal manure 570 || 78°60 175 | 1965 | 21-40

Mineral and Ammoniacal manure

June 16.) Whole plant ...
Mineral and Ammoniacal manure

June 36.) Whole plant

55-7 || 77:38 | 323 | 19:39 || 22-69
8250 | 030 | 17-20 |) 17-50

Barley; 1857.

June 24,| Whole plant 25.0. sc. c.c0ceeeses 0x4 HUman ved 3 oc ccccracncsrosassuscersacs | 86 | 85°12 3-93 | 10-95 || 14-88
June 24.) Whole plant .........:cesereseeree Unmipriupedy 2. te-: sovsse+anesccacnos || 20:9 } 81-48 1:97 | 16°55 | 18-52
! ‘

June 17./Whole plants coming into Flower |Unmanured 543 || 79:74 516 15:10 || 20:26 |
June 17.|Whole plants coming into Flower |Unmanured 415 || 86°74 410 916 | 1326 |
June 17. Whole plants coming into Flower |Ammoniacal manure || 52:5 || 80°38 4°38 15-24 | 19-62
June 17./Whole plants coming into Flower |Ammoniacal manure 50-4 | 84°33 4:36 1131 15°67

Clover; 1857. j
PAupS LOH GANS ic.c-c 05s .20s. cosece-ceence ees Unmanured 85°61 6-00 | 839 || 14-39
Aug. 10.|Stems and Leaves ... Unmanured 83-23 | 233 | 14-44 | 16°77
Aug: ))1-|Headsi$s.c2-<-..--5 225+ Unmanured 87-15 189 | 10-96 || 12-85

78:32 | 131 {| 20-37 || 21-68
{ v

Aug. 11. Stems and Leayes Unmanured

These experiments also tend to show that the reducing-power of certain of the
carbon compounds of the plant was sufficient to convert nearly all the oxygen (or ozone)
present into carbonic acid, when in the shade.

The next point is to consider how far the conditions are favourable to the oxidation
of Nitrogen in the vegetable organism, when the plant is subjected to the action of the
direct rays of the sun.

Experiments, Series 3.

In these experiments, in which over 100 exhaustions were made, the operation was
conducted precisely as in the case of the last experiments, with the exception that the
plants were exposed during the whole process to the direct rays of the sun. The
following Table exhibits a few of the results obtained, which are sufficient for our
present purpose.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 489

Tasie I1I.—Showing the amount and composition of the Gas given off into
a Torricellian vacuum, by plants exposed to sunlight.

|| >,
| Total | Per cent.
Gas col-| |
Date. How manured, &e. | lected, | Nite | Gare Oxygen
| cub. See) Gxeoerd nanan Wiser
| cents. } gen. vo acid. Carbonic]
| | | acid.
Wheat (whole plant), 1858.
june aeeWnmanired rem ..to ek ee Leelee 173-65 [21-17 | 5-18 || 26-35
Tine wee 254 W oman Ted icort soak cacideccones ecncatiecaeuos setae sesleccssntese 34:8 || 77-01 | 21-26 | 1-73 || 22-99
Pune sO Ummanured ~ncccnencenacsee etemcemcceratercscdscirciccdsacinns 44-1 || 72-79 | 20°86 | 6°35 || 27-21
June 22.|Mineral and Ammoniacal manure................0.+2-+--|, 54°5 || 73°76 | 21-29 | 4:95 || 26-24
June 23. |Mineral and Ammoniacal manure..........2...-se0eee+2|, 42°71 | 78°15 | 15°44 | 6°41 | 21°85
June 25,|Mineral and Ammoniacal manure................2+++ .s..{ 37-2 || 78°76 | 19°09 | 2-15 | 21°24
Grass (whole plants), 1857.
August 15.|Mineral and Ammoniacal manure: second crop ...... 39°0 | 82:10 | 1619 | 1°71 | 17-90
August 15. |Mineral and Ammoniacal manure: second crop ...... || 47-8 | 77°08 | 15:35 | 7-57 | 22-92
August 15. Mineral and Ammoniacal manure: second crop ...... 41-6 || 76:56 | 21-46 | 1-98 || 23-44
August 17. Mineral and Ammoniacal manure: second crop...... I 39°9 || 75°07 | 23°39 | 1°54 || 24-93
August 18.|Mineral and Ammoniacal manure: second crop...... | 36°38 || 79°88 | 15°19 | 4:93 | 20-12
August 18.|Mineral and Ammoniacal manure: second crop...... || 42:3 (50° 23 |15°97 | 3°80 || 19°77
Beans, 1858.
July 12. Mineral manure ; almost podding ............seeceeeee ees | 44:3 71: 11 lis 8°28 | 10°61 || 28°89
July 12. |Farm- yard manure ; almost peers .|| 45°8 73° 14 | 10°26 | 16-60 || 26°86
July 15. ‘Unmanured ; almost podding .... --|| 25:9 | 82: 63 |15°83 | 1°54 || 17°37
July 15.|1 Mineral and Ammoniacal manure ; aimene podding. ..|| 80°99 || 70°55 | 20°71 | 8°74 || 29°45

The general accordance in the proportions of Nitrogen found throughout this Series,
together with their general approximation to the amounts observed in Series 2 (Table IT.),
and the consequent similarity in range of the sums of the two remaining gases—carbonic
acid and oxygen—point to the character of the change which has taken place, by virtue
of which the proportion of carbonic acid is diminished, and that of oxygen increased.
The variations in the amounts are, nevertheless, somewhat considerable; and we feel
that it would be requisite to exercise considerable caution in attempting to refer them
to any other than accidental circumstances beyond our control. There can be no doubt,
however, that the carbonic acid, shown to exist in the plants in the shade, has yielded
the oxygen evolved when in the sunlight. But the mutual relations of the two gases will
be more clearly brought to view by a consideration of the results yet to be adduced.

Experiments, Series 4.

These experiments, as well as those of the succeeding Series, were arranged to show
the influence of the time of action of the sunlight on the plant, upon the relative pro-
portions of carbonic acid and oxygen.

In the Series of experiments now under consideration, duplicate quantities of the

3x2

490 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

plant were operated upon at the same time. Both were prepared in the shade; an
then the vessels containing them were each entirely excluded from the light, by means
of a thick paper covering. In this condition each was attached to a Torricellian ex-
hauster*. The paper was then removed from one of the vessels so as to expose it,
with its contents, to the direct rays of the sun; the other vessel, with its enclosed plant,
remaining covered. ‘The exhaustion of both was then commenced immediately, and the
action continued for half an hour.

The following Table shows the results obtained in this manner, in sunlight, and in
the dark, respectively.

TasLe IV.—Showing the amount and composition of the gas evolved, during half an
hour, into a Torricellian vacuum, by duplicate quantities of plant, both kept in the
dark for some time before commencing the exhaustion, then one exposed to sun-
light, and the other kept in the dark, during the process.

(1858.)
Per cent.
Date. |Description} Conditions during || Total Gas : gp

? of Plant. Exhaustion. collected. Nitrogen. | Oxygen. pri pOxyeonand
i | acid.
cub. cents.

B In dark......... 25-7 66-93 2°33 | 30°74 | 33-07

fans +++!) In sunlight ...|| 364 69°78 8:24 | 21-98 | 30-22

In dark......... 28°3 81-63 3:53 | 14:84 || 18-37
99 i
Tale) OS ae In sunlight ...| 25:9 || 70-27 | 1313 | 1660 || 29-73 |

Inidankeeesces 26°4 73-11 8:33 18°56 || 26:89
July 23. |Oats...... In sunlight a2-7 || 72-25 | 16-74 | 11-01 || 27-75 |
}
In dark......... 27-4 68:25 5°11 | 26:64 || 31-75 |

Daly2S: Oats eset {tu sunlight ...| 29-2 || 67-47 | 19°86 | 1267 || 3253

In dark......... 31-4 77°39 6-69 15-92 | 29-61

ahaa Oats: In sunlight ...| 21-7. || 76-50 | 1659 | 691 || 23-50

The amounts of carbonic acid and oxygen recorded in the Table, indicate very clearly
the ready transformation of the one into the other—or, rather, the transformation of
carbonic acid into a solid carbon compound, and free oxygen. In reference to the
question we are considering, these results have a high importance, as showing the great
reducing-force manifested under the influence of the sun’s rays, by which the carbonic
acid is so suddenly reduced.

* This term, for convenience, we apply to the apparatus which has been described at p. 487, by which the
plant in the vessel, fig. 7, Plate XII, is exhausted.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 49]

Experiments, Series 5.

This set of experiments was arranged to show how far the reduction of the carbonic
acid, with the evolution of oxygen, was due to the action of the sunlight, in conjunction
with the fluids of the plant, at the moment of the passage of the gas through the walls
of the cells.

If the decomposition of the carbonic acid resulted from a physico-chemical action, in
the presence of sunlight, upon this gas only as it passed through the cell-walls, then
there might be no oxygen liberated in the growing cell. If, on the contrary, it were
decomposed before passing out of the cell, free oxygen would exist within the latter.

To settle this question, a set of experiments was made exactly similar to those the
results of which are given in Table IV., with the exception, that now the time of the
exhaustion, and of the action of the sunlight, was reduced to four or five minutes, and
the quantity of plant operated upon was increased, so as to give sufficient gas for
analysis during this short period. The following Table gives the results obtained.

Taste V.—Showing the amount and composition of the Gas evolved into a Torricellian
vacuum, during four or five minutes only, by duplicate quantities of plant, both
kept in the dark for some time before commencing the exhaustion, then one still
kept in the dark, and the other exposed to sunlight during the short period of the

operation.
(1858.)
| Per cent.
Date. |Description} Conditions during | Total Gas “ ae
of Plant. Exhaustion. | collected. || Nitrogen. | Oxygen. Carbone Cayeen and
| : acid.
| cub. cent. 6
: In dark......... | 41-7 7242 | 3 23°98 27-58
FO NO Seco In sunlight | 42-5 || 7223 | 4-71 | 2306 || 27-77
(oe : In dark......... | 55°7 71-46 3:23 | 25-31 28°54
July 30. |Oats...... In sunlight ...|) 43°3 || 69°98 3°23 | 26:79 || 30:02
In dark......... | 37-9 | 93:11 | 686 | 1003 || 16-89
POSES Sane {i sunlight ...| 385 || 77-14 | 9:09 | 13°77 || 22-86
In dark......... | 344 || 73-49 | 7-07 | 14:24 || 21-51
feb Oats ws! 4 Ip sunlight ...| 41°38 |) 75°84 | 7:89 | 16:27 || 24-16

The above results show that the carbonic acid can pass through the cell-wall, in the
presence of sunlight, without suffering decomposition. It would hence appear that
the free oxygen which a plant yields after it has been for some time under the influence
of the direct rays of the sun, existed as such in the cells before the exhaustion. The
slight preponderance of oxygen observed in the gas exhausted in sunlight is doubtless
due to its action upon the carbonic acid within the cell, during the short period of its
operation upon it before it passes out; precisely analogous to the action when the
plant is subjected to ordinary atmospheric pressure.

492 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

Experiments, Series 6.

In order to bring out more clearly the influence of sunlight before the exhaustion, a
series of experiments were made, in which two vessels, containing the duplicate quan-
tities of plant, were each kept covered with paper for some time, and then, from twenty
to thirty minutes before commencing the exhaustion, the paper was removed from one of
them, both being then exhausted,—the process continuing ten, fifteen, or twenty minutes.
The following results were obtained.

Taste VI.—Showing the amount and composition of the Gas evolved into a Torricellian
vacuum, by duplicate quantities of plant, both kept in the dark for some time, and
then one exposed to sunlight for about twenty minutes, when both were submitted
to exhaustion.

Boer (PA ee Ee as
itietict ES Os aah
Duie. orl | Exhaustion, || ealledod: | wigan | Oxygen. | Onrtonie |Caveenand
y 7 Hi gent
Buty 31. }Oats | {7 Bath BED ae | et93 | 633 | 3131 |
dee toa Onistn PEpEarerr sme pe ces | eet ae eer ere | see
||
pop. loan) {Baath gor | goag | eae | n4ua | a
| |
Aug. 2 (Oats.....14 fp em TE lee ge sabes JIT eee ih cere
Aug. 8 (Oats... {Tr Sogit | aer | 6636 | 3033 | 311 | 3364
cvey eae eee ah a gE
Aug. 8. )Oats....../ 72 Surcke | ioy || ge40 | eea3, | 457 eres

The comparison of the results in this Table with those in Table V., shows that the
oxygen must have been liberated from the carbon, and been retained within the cells,
until the instant of the exhaustion, as the gas was evolved from all parts of the leaf,
and not from the surrounding water, as soon as the pressure was remoyed.

The conclusions to be drawn from the above several Series of experiments are not
without an interesting bearing upon our present subject.

1. Carbonic acid, within growing vegetable cells, and intercellular passages, which
are penetrated by the sun’s rays, suffers decomposition with the evolution of oxygen,
the latter remaining in the plant or being evolved from it. This takes place very
rapidly after the penetration of the sun’s rays.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 495

2. Living vegetable cells, &c., which are in the dark, or are not penetrated by the
direct rays of the sun, consume the oxygen they contained very rapidly after being
placed in such circumstances, carbonic acid being formed.

3. There can hence be little or no oxygen in the living cells of plants during the
night, or during cloudy days. The presence of oxygen in the cells of thick-leaved
plants, or in the deeper layers of fruit, is also very problematical.

4, With every cloud that passes oyer the sun, the oxygen of the living cell will oscil-
late under the influence of the reducing-force of the carbon-matter, forming carbonic
acid, on the one hand, and of the reducing-forces of the associated sun’s rays, liberating
pure oxygen and forming a carbon-compound containing less oxygen than carbonic acid,
on the other.

5. The idea is suggested by the above considerations, that there may be in the outer
cells, which are penetrated by the sun’s rays, a reduction of carbonic acid, and a fixation
of carbon, with the evolution of oxygen, at the same time that, in the deeper cells, the
conyerse process of the oxidation of carbon and the formation of carbonic acid is taking
place. If such be the case, the oxygen of the outer cells would, according to the laws
in conformity with which the diffusion of gases and their passage through tissues are
known to take place, be continually penetrating to the deeper cells, and there oxidizing
their carbon-matter into carbonic acid; whilst the carbonic acid thus formed would
pass in the opposite direction to be decomposed in the sunlight of the outer cells. As
the process of cell-formation went forward, and the once outer cells became buried
deeper by the still more recent ones above them, they would gradually pass from the
state in which the sunlight was the greater reducing-agent, to that in which the car-
bon-matter of the cell became the greater—from the state in which there was a flow
of carbonic acid to them and of oxygen from them, to that in which the reverse action
took place. The effect of this action may be the formation of oxidized products—acids,
or saccharine matter, &c.—in the deeper cells, whilst the great reducing-power of the
sun’s rays may form more highly carbonized substances in the outer cells, which in their
turn become subject to oxidation when buried deeper. ‘The physical and physiological
phenomena of such interchanges are obviously worthy of a closer study ; but the subject
is too wide for any further development here.

6. The very great reducing-power operating in those parts of the plant where ozone
is most likely, if at all, to be evolved, seems unfavourable to the idea of the oxidation of
Nitrogen into nitric acid by its means—that is to say, under circumstances where the
much more readily oxidizable substance, carbon, is not oxidized, but on the contrary its
oxide, carbonic acid, is reduced; whilst, as has been seen, when beyond the influence
of the direct rays of the sun, the cells seem to supply an abundance of the more easily
oxidized carbon, in a condition of combination readily available for oxidation by free
oxygen, or ozone, should it be present. The conclusion that free Nitrogen would not
be likely to be oxidated into nitric acid within the structures of the plant, seems to
be borne out by the well-known fact, that nitrates are as available a source of Nitrogen

494. MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

to plants as ammonia; and hence, if we were to admit that Nitrogen can be oxidated
into nitric acid in the plant, we must suppose, as in the case of carbon, that there are
conditions under which the oxygen compound of Nitrogen is reduced within the
organism, and that there are others in which the reverse action, namely, the oxidation
of Nitrogen, can take place. In relation to this question, it may be mentioned that
several specimens of green Wheat and Grass which had been liberally manured with
nitrates were examined for nitric acid, but no trace of it was found in them.

7. To the foregoing six conclusions, another may be here added relating to this sub-
ject, though deduced from the results of experiments on the decomposition of organic
matter, which will be referred to more fully presently (p. 509 et seq.). So great is the
reducing power of certain carbon-compounds of vegetable substances, that when the
vital (growing) process has ceased, and all the free oxygen in the cells has been con-
sumed, in the formation of carbonic acid, water is decomposed, and hydrogen is evolved.
This process does not, however, continue long, showing that the cell provides a certain
amount of matter more easily oxidized than the remainder, or that the entire cell-
matter, after becoming slightly oxidized, loses its energetic reducing-power. ‘The former
alternative is the more probable one.

The foregoing considerations with regard to the intensity of the reducing action of
certain of the carbon-compounds in plants suggest the idea of a possible source of Ozone,
very analogous to that by which it is ordinarily obtained by means of phosphorus. As
is well known, the process consists in allowing oxygen to come into incomplete or only
instantaneous contact with phosphorus. This substance having an intense avidity for
oxygen, a part of the latter unites with it to form an oxygen-compound of phosphorus,
when, if the contact be not too long, another part passes off in the state of Ozone.
Certain carbon-compounds of the vegetable cell have also a great affinity for oxygen in
the dark (p. 488); and the oscillations of the affinities, due to the degree of light (pages
489-492), and to the depth of the cell (p. 493), would afford conditions of molecular
action somewhat similar to those under which Ozone is produced in the presence of phos-
phorus. According to this analogy the Ozone would be due to the action of the carbon-
compounds of the cell on the common oxygen eliminated from carbonic acid by sun-
light, and not to the direct action of the sunlight itself. The Ozone thus formed, if not
instantly evolved from the plant, would be destroyed by the easily oxidizable carbon-
compounds present. It is more probable, however, that the Ozone, stated by Dr Luca
and others to be observable in the vicinity of vegetation, is due to the intense action of
the oxygen of the air upon the minute quantities of volatile hydrocarbons emitted
by the plants, and to which they owe their peculiar odours, than to any action going
on within the cells. The rapidity of the oxidation in the air of the hydrocarbons,
and the volatile principles of plants generally, goes to favour the view here suggested ;
so also does the fact, that Ozone has been observed most readily in the vicinity of such
plants as are known to emit freely essential oils—as, for instance, those of the Labiate
family,

THE SOURCES OF THE NITROGEN OF VEGETATION, ETc. 495

Since it would appear that, under certain circumstances, Ozone is formed in the im-
mediate vicinity of some plants, it remains to consider the possibility of its acting, in an
indirect manner, as a source of combined Nitrogen to our experimental plants—that is,
through the agency of the materials involved in the experiment—and thus compromising
our result in regard to the question of the appropriation, by the plant itself, of free or
uncombined Nitrogen. It might so act :—

1. By becoming absorbed by the water that condenses within the vessel enclosing the
plant, and then oxidizing the free Nitrogen dissolved in the water.

2. By being absorbed by the soil—either directly from the air of the enclosing appa-
ratus, or from the condensed water returned to the soil—and then, in connexion with
it, as a moist, porous, and alkaline body, forming nitrates in the manner referred to
by PrLovuze and Fremy*, in their remarks upon the experiments of CLozz which we
have shortly described at p. 465 of this paper.

3. By passing down in solution in water, or in the gaseous state, to the older and
decomposing parts of the roots, and there forming nitric acid by the oxidation either of
the free nitrogen contained in the older cells, or of that evolved in decomposition.

These questions have not been so fully investigated as, considered as independent
subjects of inquiry and with reference to the results obtained by ScHONBEIN and others,
would be desirable. But so far as they can have a bearing upon the sources of error in
our experiments upon the question of the assimilation of free Nitrogen by plants, they
have received our careful consideration.

C.—Experiments on the action of Ozonized air on decomposing Organic matter,
and porous and alkaline substances.

Experiments were made to ascertain the influence of Ozone upon organic matter, and
certain porous and alkaline bodies, under various ‘circumstances. The action of ordinary
air upon sticks of phosphorus was had recourse to as the source of the Ozone. The
arrangement was as follows:—Three large glass balloons (carboys), each of about
40 litres capacity, were connected together by glass tubes which passed through
stone-ware stoppers fitted into their mouths, the joints being made tight with calcined
gypsum cement. The bottom of each vessel was covered with water to the depth of
about half an inch, so that, when pieces of phosphorus were put in, they were partly
covered with the fluid. A tube, which could be opened or closed at pleasure, was fixed
through each stopper for the supply of water, and fresh phosphorus, as needed. An
Allen and Pepys gasometer, capable of holding about 2 cubic feet of air, was con-
nected by a glass tube with the first of the series of vessels; and by its means,
air could be forced in a continuous stream through the three vessels containing the
phosphorus. On passing out of the last of them it was led through a wash-bottle, and
then into a glass vessel, from which, by means of a number of glass tubes passing from
it, it was distributed into bottles containing the substances to be submitted to the action

* Traité de Chimie Générale, tome sixiéme, p. 343 (1857).

MDCCCLXI. 3 Y

496 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

of the Ozone. Thus, all the ozonized air passed the wash-bottle in its course from the
balloons to the distributing apparatus.

The following substances were subjected to the action of the Ozone—each substance,
or mixture, being enclosed in a glass bottle of about 1:5 litre capacity, fitted with an
exit-tube in which were fragments of pumice saturated with sulphuric acid :—

(1) $b. ofignited soil, moistened with 100 cub. centims. water, this being just sufficient
to make it slightly coherent.

(2) 41b. of ignited soil, 300 cub. centims. water, 2-5 ounces boiled starch, and 2°5 ounces
dry starch.

(3) $b. of ignited soil, 200 cub. cenitms. water, and 2°5 ounces saw-dust.

(4) 2:5 ounces saw-dust, and 100 cub. centims. water.

(5) $1b. of ignited soil, 200 cub. centims. water, and 2°5 ounces bean-meal.

(6) 31b. of ignited soil, 150 cub. centims. water, and 2°5 ounces bean-meal.

(7) 2:5 ounces bean-meal, and 50 cub. centims. water.

(8) 1 1b. garden-soil.

(9) 1b. of slaked lime, and 2°5 ounces bean-meal, made slightly pasty with water.
(10) $1b. of slaked lime, some starch, and saw-dust, made slightly pasty with water.
(11) 2:5 ounces of boiled starch, 2°5 ounces fresh starch, and 200 cub. centims. water.

All the bottles were placed before a window where the sun shone directly upon them
for a considerable part of the day, as it did also for some hours daily upon the
balloons.

Every day, about 9 o’clock in the morning, the cylinder of the gasometer was raised,
and a slow current of air passed through the apparatus during about two hours. This
process was generally repeated once or twice more during the day. The experiment
commenced in April, and continued till the following autumn; that is, through all the
warm weather of the summer, when a thermometer in the room frequently stood at 25°
to 29°C. The amount of Ozone passing through the apparatus was so great, that the
vulcanized caoutchoue which connected the tube from the last balloon with that passing
into the wash-bottle was cut off with the passage of three or four gasometerfuls of air.
The joint was then made by fixing a piece of larger glass tubing over the point of contact
of the smaller connecting tubes, and closing the ends of the larger tube with corks well
fitted upon the smaller ones.

Once every three or four days a small piece of phosphorus was dropped into each
balloon. In this way the action was sufficiently maintained to produce a distinct odour
of Ozone in the room whilst the air was passing.

During the first half of the period of the experiment, a wash-bottle filled with large
lumps of pumice, and about half-full of a solution of caustic potash, was used; so that
the ozonized air in bubbling rapidly through the solution continually threw it up, by
which means the pumice was kept moistened with it.

A careful examination of this liquid, together with the washings of the pumice, failed
to detect any nitric acid. About the Ist of July, the alkaline wash was replaced by a

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 497

bottle containing only pure water. The latter also, at the termination of the experi-
ment, failed to give evidence of even traces of nitric acid.

At the termination of the experiment, the contents of each of the eleven bottles were
also examined. A portion was exhausted with water, and the extract concentrated by
boiling, after the addition of permanganate of potash to destroy the organic matter.
The excess of permanganic acid was removed by carbonate of lead, and the clear solu-
tion filtered off from the precipitate. Each solution so obtained was tested for nitric
acid; but in no case, excepting that of the garden soil, was there any indication of its
presence. An examination of the original garden soil showed that it contained nitric
acid before being subjected to the action of the Ozone.

Owing to the negative character of the above results, it is not necessary to describe
the apparatus, and the circumstances of the experiments, in any more detail, which would
have been desirable had the results been of a positive kind.

We are, however, by no means prepared to infer, from the evidence just adduced, that
under no circumstances in nature is it possible for Ozone to transform nitrogenous com-
pounds of the ammonia class, or the nascent nitrogen evolved during decomposition,
into oxides of Nitrogen. We would not say that it may not be possible for Ozone to
form such compounds when in connexion with non-nitrogenous bodies or porous sub-
stances permeated with gaseous Nitrogen, or even in the atmosphere. Nor are we pre-
pared to maintain that the nitric acid in soils is not in part due to some of these causes.
These questions will require much further investigation before they can be satisfactorily
settled. To some of them we shall refer again presently.

But we wish particularly to call attention to the fact that, in the experiments just
referred to, there was a very much larger quantity of Ozone, acting upon organic matter,
soil, &c., in a very wide range of circumstances, and for a much longer period of time,
than was involved in our experiments on the question of the assimilation of free Nitro-
gen by plants. Yet there was no appreciable quantity of nitric acid formed. It may
therefore be concluded that there will be no error introduced into the results of the
experiments on the question of the assimilation of free Nitrogen by plants themselves,
arising from the action of Ozone upon free Nitrogen under the circumstances of the
experiments, and so providing to the plants an unaccounted supply of combined

Nitrogen.

D.—Lvolution of free Nitrogen in the decomposition of Nitrogenous organic compounds.

Two obvious methods of investigating the question, whether or not free Nitrogen is
given off in the decomposition of nitrogenous organic matter, present themselves.

1. To allow the organic matter to decompose under circumstances in which any free
Nitrogen that may be evolved can be collected and estimated.

2. To allow the organic matter to decompose under circumstances in which the total
amount of the compounds of Nitrogen formed in the process can be estimated—the loss
of Nitrogen then representing the free Nitrogen evolved.

3¥2

498 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

A number of experiments according to the first of these methods has been made by
Reiser. He submitted nitrogenous animal and yegetable substances to decomposition
under an enclosing vessel in ordinary air, into which he passed oxygen as that of the
air was consumed, His result was, that the amount of Nitrogen in the air was gradually
increased. He does not appear, however, to have completed the inquiries on this sub-
ject which he proposed to undertake.

The second method has been followed by M.G. Vititz. The conclusion he arrived at
was, that in the decomposition of several nitrogenous vegetable substances, about one-
third of their total Nitrogen was evolved in the free state.

The losses of Nitrogen which M. BoussinGav.t’s experiments on the question of the
assimilation of free Nitrogen by plants indicated, when he used nitrogenous organic
matter as manure, rendered it desirable to investigate the subject in its bearings upon
the conditions provided in our own experiments on that question. The following plan
was adopted :—

A given weight of nitrogenous organic matter, the percentage of Nitrogen in which
had been previously determined, was mixed with burnt soil, or pumice, prepared as for
the experiments on the assimilation of Nitrogen by plants (p. 471), and put into a bottle
of about 360 cub. centims. capacity, as shown at B, fig. 8, Plate XII. A proper quantity
of water was added; and then the bottle was closed with a cork, through which were
tightly fitted two bent glass tubes, which passed externally in opposite directions. One
of these tubes was connected with an eight-bulbed apparatus A, containing sulphuric
acid, for the purpose of washing air drawn through it into the rest of the apparatus.
The other tube, passing from B in the opposite direction, was connected with a similar
eight-bulbed apparatus C, containing a solution of oxalic acid. From this again passed
a tube extending, through a cork, to the bottom of a second bottle D (similar to B),
which contained some sulphuric acid. Through the cork of the bottle D another tube
E also passed, but it did not dip into the sulphuric acid. It is obvious that, on drawing
the air from D by means of the tube E, a current of air would pass inwards through
the sulphuric acid in A, into the bottle B, then through the oxalic acid in C, and so on.
In this way, the air of the vessel B, containing the decomposing organic matter, could
be renewed at pleasure by fresh air, washed free from ammonia. At the same time, any
ammonia evolved from the decomposing organic matter was drawn into the eight-bulbed
apparatus C, and there absorbed by the oxalic acid. At the termination of the experi-
ment, the combined Nitrogen remaining in B, and that retained in the form of ammonia
in the oxalic acid in C, were determined. The difference between the total amount of
combined Nitrogen so found in the products and that originally contained in the organic
substance submitted to decomposition, is taken to represent the amount of nitrogen
given off, in the free state, during the process.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 499

Series 1.—Ewperiments on the decomposition of nitrogenous organic matter,
made in 1857.

Wheat-meal, Barley-meal, and Bean-meal were the nitrogenous organic substances
submitted to decomposition. A quantity of each of these was mixed respectively
with burnt soil and with pumice, making in all six separate experiments. About 100
grammes of soil, or about 60 grammes of pumice, were used—these quantities, together
with the meal, filling the bottles B to the depth of about 2 inches. Sufficient water
was added to bring the mixture into an agglutinated condition. The materials being so
prepared, the apparatus was put together according to the arrangement above described.
The six sets were then placed in a light room before a large window, so that, during the
middle of the day, the sun shone directly upon them.

The experiments commenced on June 10, and terminated on October 8,1857. Several
litres of air were drawn through each apparatus daily, by applying the mouth to the
tube E. After the first day the gas possessed a more or less disagreeable taste, and the
odour of decomposing organic matter.

The following statement of the condition of the several mixtures, at the termination
of the experiment, is condensed from the notes then made :—

1. Wheat-meal and ignited Pumice—The meal slightly mouldy; the odour that of
decomposing organic matter; quite moist, so that the particles of pumice adhered
together.

2. Wheat-meal and ignited Soil—A slight mouldy coating on the surface ; odour like
that of No. 1; the mass moist, but not sufficiently so for the particles of soil to aggluti-
nate. :

3. Bariey-meal and ignited Pumice.—No mouldy coating on the surface ; odour similar
to that of the wheat but more intense, and sour, much like that of fermenting malt ;
the mass wet and clammy.

4. Barley-meal and ignited Soil—No mouldy coating on the surface ; odour like that
of barley No. 3; sufficiently moist to agelutinate.

5. Bean-meal and ignited Pumice.—A little mould upon the surface, but not quite so
much as with the wheat and soil (No. 2); odour very disagreeable and putrescent; the
mass wet and clammy.

6. Bean-meal and ignited Soil. Very similar to the bean-meal and ignited pumice
(No 5), but a little more wet and pasty.

In every case, carbonic acid was evolved on the addition of oxalic acid, preparatory to
evaporating to dryness. The evolution was the greatest from the bean-meal with soil.

A known proportion, about one-half, of each dried mass, was burnt with soda-lime,
and the Nitrogen capable of estimation in that way determined. The remainder was
reserved for the determination of nitrates, provided any were present. On examination,
however, no nitric acid was detected. To put the validity of the qualitative test for
nitric acid beyond doubt, 0-001 gramme of nitric acid was added to the portion of sub-
stance which had been already exhausted to test for nitric acid, and had yielded a nega-

500 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

tive result. The mass was then re-exhausted with water, and the extract submitted to
’
precisely the same process as before, when the presence of nitric acid was made manifest.

In the following Table are given the numerical results of the six experiments :—

TaBLeE VII.—Showing the Numerical results of experiments on the Decomposition of
Nitrogenous organic matter, made in 1857.

Substances submitted to experiment. Nitrogen after Decomposition. |

3 tit | Q tity i Not recovered. |
Description of Ae: of SURRY ay ROBDMEY |b otek by
Oreanid matter. | Description of Matrix.| of * Meal 2 Of Soda-lime. Actual
8 taken. || Nitrogen. Actua Per cent. |
| | quantity.
grammes. grammes, grammes. grammes.
il Wheat-meal...|[gnited pumice ...| 2°0585 | 0:0370 | 0°0338 | 0°0032 8°51
2. Wheat-meal.,.,[gnited soil ......... 2°1282 || 0:0383 | 0:0335 0°0048 12°53
|
3. Barley-meal...|/I[gnited pumice .,,| 2°2495 0:0380 | 0-0368 0:0012 3°16
4. |Barley-meal...|Ignited soil ......... 20980 | 0:0355 | 00309 | 0-0046 12-96
5. Bean-meal .../Ignited pumice ...} 20650 | 0:0803 | 0:0741 | 00062 | 7:72
6. Bean-meal .../Ignited soil ......... 2:0800 || 0-0809 | 0-0823 \(+0-0014) |+ (1°73) |

The last two columns of this Table, which exhibit respectively the actual amount of
Nitrogen not recoverable by the soda-lime process in the substance after decomposition,
and the percentage proportion of this loss upon the Nitrogen submitted to experiment,
are the most important to consider for our present purpose.

With one exception (the gain of Nitrogen in which is quite within the range of the
error of analysis), all the experiments point to the fact, that a part of the Nitrogen of
decomposing organic matter passes into a state in which it cannot be estimated by the
soda-lime process. Neither did it exist as nitric acid. There appears, therefore, to be
an evolution of free Nitrogen.

It is not a little remarkable, that although so large a proportion of the total Nitrogen
present is lost, doubtless passing off as free Nitrogen, yet scarcely a trace of ammonia
was given off from the mass; for the oxalic acid in the bulb-apparatus C was, in each
case, separately rendered alkaline with caustic potash and distilled, the distillate being
collected and examined quantitatively for ammonia, when, in only one case—that of the
Bean-meal and Pumice—was there any ammonia indicated, and then only equal in
amount to 0:0002 gramme Nitrogen. This was the case, notwithstanding that the
Nitrogen in the mixtures amounted to from 0:03 to 0-08 per cent. of their entire
quantity.

The questions here arise :—to what extent had the decomposition of the organic sub-
stance proceeded? what shall we accept as the measure of the amount of decomposition ?
what are the intermediate stages through which the substance has passed? what is the
character of the organic compounds remaining in the mass? what is the nature of those
that have been evolved? and what part does water play in the matter?

The subject of the character of the gradual changes which take place during the

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 501

decomposition of mixtures of nitrogenous and non-nitrogenous substances, in variable
proportions, in connexion with soil and water, involves points so highly complicated,
that we cannot pretend satisfactorily to answer all the above questions.

We may, however, ascertain the character of some of the final products of the decom-
position, and from a knowledge of these draw conclusions as to the changes of which
they are the result under various circumstances.

Series I1.—Evperiments on the Decomposition of nitrogenous Organic Matter, made
im 1858.

The following series of experiments was made with a view to embrace a wider range
of conditions as to degree of moisture ;—to observe the different stages of decomposition
as manifested by the odour, &c. ;—to include the circumstances of sprouting, early growth,
and subsequent decay of the products of the vegetation ;—and to afford material for a
more elaborate inquiry into the character of the products of the decomposition.

The results given above, in Table VII., do not show any difference between soil and
pumice as matrix that we can safely refer to other than incidental causes independent
of the action of the matrix itself. Yet we continue the use of the two substances, in
order to see if, with a larger percentage of organic matter, and a more complete decom-
position, the pumice will retain the ammonia formed as well as the soil.

About 175 to 200 grammes of soil, or 120 to 150 grammes of pumice, were used as
matrix in each experiment, and the other conditions were as follow :—

i a. 171 seeds, weighing 8-0475 grammes, 50 c. c. water, with ignited Soil.
Wheat.< b. 171 seeds, weighing 80715 grammes, 100 c. c. water, with ignited Pumice.
Be Meal, weighing 9°8810 grammes, 40 c. c. water, with ignited Soil.

i a. 163 seeds, weighing 8:0440 grammes, 50 c. c. water, with ignited Soil.
b. 165 seeds, weighing 8:°1360 grammes, 100 c. c. water, with ignited Pumice.

Barley.
iE Meal, weighing 8-9670 grammes, 40 c. c. water, with ignited Soil.

a. 7 seeds, weighing 64700 grammes, 50 c. c. water, with ignited Soil.
Bean. <4. 7 seeds, weighing 5°7830 grammes, 50 c. c. water, with ignited Pumice.
¢. Meal, weighing 61750 grammes, 40 c. c. water, with ignited Soil.

Those of the mixtures to which about 50 cub. cent. of water were added, were about
as moist as soils when in a good condition for vegetable growth. Those with 40 cub.
cent. were much drier in appearance, there being no tendency to agglutination of the
particles. Those with 100 cub. cent. were very wet, there being some free water above
the solid matters.

The seeds sown with 50 cub. cent. water showed growth in a few days after being
put in, and the vessels (B, fig. 8, Plate XII.) were soon filled with a mass of vegetation.
Those sown with double this quantity, or 100 cub. cent. water, showed no indications
of sprouting; and in a few days, the odour evolved from them showed that decompo-
sition had set in. The mixtures of meal and soil, also, soon gave odours indicative of

502 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

decomposition, though less foul than those from the whole seed and 100 cub. cent.
water.

The following Notes, taken at different times during the experiments, will indicate
the stages of growth, or decomposition, through which the several organic matters
passed.

March 16.

Wheat (a)—Seeds, in Soil with 50 cub. cent. water —Came up some days later than the
corresponding Barley ~; has not grown so rapidly; has kept green for a longer period ;
and is yet growing healthily, though much crowded in the small bottle. The air pass-
ing from the bottle has not the odour of decomposing organic matter. There is a slight
mould on the soil due to a few seeds which did not grow.

Wheat (b)—Seeds, in Pumice with 100 cub. cent. water—The Pumice in this case was
covered with water to the depth of about one-fourth of an inch, and a few grains floated
in the water. In a few days the air drawn through the bottle gave the odour and taste
of decomposing organic matter. At the end of about a month the free water on the
surface began to disappear rapidly, and in a short time it was all gone, leaving a grey

mouldy coating of organic matter over the top of the pumice. This disappearance of
water was too great to be due to simple evaporation in the air passed through the appa-
ratus. It was doubtless consumed in the process of decomposition—a view which
receives confirmation from our experiments on the nature of the gases evolved during
decomposition.

Wheat (c)—Meal, in Soil with 40 cub. cent. water.—Gives little indication of decompo-
sition by the air which passes from it. Compared with Wheat 0, the difference in this
respect is very marked.

Barley (a)—Seeds, in Soil with 50 cub. cent. water —Came up soon after being put in,
grew rapidly, and in five weeks had grown to the top of the bottle, a height of about
5 inches. By the end of February the bottle was quite filled with green vegetable
matter, and up to that time no odour of decomposition was distinguishable in the air
which was passed through, but from that date the leaves became yellow, and decompo-
sition has been manifested both by appearance and the taste of the air.

Barley (6)—Seeds, in Pumice with 100 cub. cent. water.—Progress almost exactly similar
to that of the corresponding Wheat (2) described above.

Barley (c)—Meal, in Soil with 40 cub. cent. water.—Very like the corresponding
Wheat (c) above.

Bean (a)—Seeds, in Soil with 50 cub. cent. water—Came up a week after sowing.
The sprouts pushed several seeds out of the soil, yet they have continued to grow up to
the present time, lying upon the surface. At first there was a natural development of
leaf and of roots; but soon the latter took a remarkable course, coming through the
surface of the soil and extending through all parts of the bottle, mingling with the

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 503

stems and leaves, and forming a densely crowded mass of vegetable matter. The root-
lets from the main branches extending through the mass commenced their growth in all
directions indiscriminately, but after growing about one-fourth of an inch they invariably
turned downwards.

Bean (b)—Seeds, in Pumice with 50 cub. cent. water.—Identical in appearance with the
last (Bean a), excepting a little further developed.

Bean (c)—Meal, in Soil with 40 cub. cent. water.—Almost exactly like the Wheat (c)
and Barley (c) meals, described above.

In no one of the above nine cases was there any Ozone reaction to test-paper.

April 28.

Wheat (a)—Sceds, in Soil with 50 cub. cent. water—Twelve to fifteen stems; leaves not
unrolled, and scarcely any tendency to expansion. The vegetation not nearly so much
crowded as in the case of the corresponding Barley (a); yet most of the shoots show
signs of dying. A thin coat of fungoid growth covers the stems to the height of from
1 to 1:5 inch. The stems are from 2 to 2°5 inches high, those of the corresponding
Barley being from 3 to 4 and 5 inches high. The air passed through the apparatus is
not disagreeable either in taste or odour.

Wheat (b)—Seeds, in Pumice with 100 cub. cent. water.—The Pumice moist, but with-
out visible water, and the surface covered with a grey mouldy coating. The air has had
an unpleasant odour ever since March 16, and now it is exceedingly nauseating.

Wheat (c)—Meal, in Soil with 40 cub. cent. water—The soil apparently dry, but slightly
mouldy, and the air passed over is almost without odour.

Barley (a)—Seeds, in Soil with 50 cub. cent. water —The bottle full of vegetable matter,
all quite yellow at the top where it touches the cork, and yellowish lower down. ‘The
plants covered with a coating of greyish fungus. The odour and taste of the air slightly
disagreeable. The soil looks quite dry.

Barley (b)—Seeds, in Pumice with 100 cub. cent. water —The soil is moist and mouldy.
The mould on the surface appears to be decreasing, and is now less abundant than in
the case of the corresponding Wheat (6). The odour of the air is much less disagree-
able; indeed there is scarcely any at all.

Barley (c)—Meal, in Soil with 40 cub. cent. water—The soil mouldy and apparently
dry. The air from the vessel tasteless, and inodorous.

Bean (a)—Seeds, in Soil with 50 cub. cent. water—Continued to grow vigorously for a
long time, filling the bottle with a confused mass of stems, leaves, and roots, which has
commenced to decay rapidly during the last two weeks. The upper portions of the
mass are now entirely dead and black; but nearer the soil the stems and leayes are
green and long, whilst healthy roots are intermingled with them. The soil is also
tolerably filled with roots. The odour of the air is not disagreeable.

MDCCCLXI. 3Z

504. MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

Bean (b)\—Seeds, in Pumice with 50 cub. cent. water —Very much like the last (Bean
a with soil), excepting that the development of roots is scarcely so great.

Bean (c)—Meal, in Soil with 40 cub. cent. water.—A little mouldy matter on the surface
of the soil, which appears dry.

July 1.

Wheat (a)—Sceds, in Soil with 50 cub. cent. water.—Plants all dead; the entire con-
tents of the bottle apparently quite dry. The air has a slight musty odour.

Wheat (b)—Sceds, in Pumice with 100 cub. cent. water —Odour rather more marked
than that of the last (Wheat @); a coating of organic matter on the surface of the
pumice.

Wheat (c)—Meal, in Soil with 40 cub. cent. water.—Soil quite dry ; covered with mould ;
odour of air slight.

Barley (a)—Sceeds, in Soil with 50 cub. cent. water.—Plants quite dead and dry; air
inodorous.

Barley (b)—Seeds, in Pumice with 100 cub. cent. water.—Soil dry and covered with
mould. Air like that of Wheat 6; more foul than that of any of the others.

Barley (¢e)—Meal, in Soil with 40 cub. cent. water.—Surtace dry. The air has a slightly
musty odour.

Bean (a)—Seeds, in Soil with 50 eub. cent. water.—Plants all dead, and much deeom-
posed; forming a black mouldy mass of organic matter on the surface of the apparently
dry soil. ‘The air has no perceptible odour.

Bean (b)—Seeds, in Pumice with 50 cub. cent. water —The same as the last (Bean 2).

Bean (c)—Meal, in Soil with 40 cub. cent. water.—Soil dry ; slightly mouldy ; the air
from over it inodorous.

In order to see the effect upon the organic matter of an increased amount of moisture,
100 cub. cent. of water were added to each of the nine bottles of decomposing matter,
at this date (July 1).

August 28.
Final Report, and termination of the Experiment.

Wheat (a)—Seeds, in Soil with 50 cub. cent. water—Very little odour, and that not
unpleasant. On removal from the bottle, it was found that the organic matter was well
decomposed, only very indefinite remains of stems and leaves being visible in the soil.
On the addition of oxalic acid to the mass, to retain the ammonia during the evapora-
tion to dryness, a copious evolution of carbonic acid took place, and the surface of the
fluid was constantly covered with a brown froth during the process.

Wheat (b)—Seeds, in Pumice with 100 cub. cent. water—The mass has a disgusting
mouldy odour. The form of the grain is retained, but all the contents are gone, and the

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 505

husk is filled with fluid. On evaporation with oxalic acid, there was evolution of car-
bonic acid, &c., as with the last; indeed it was the same with all those which follow.

Wheat (c)—Meal, in Soil with 40 cub. cent. water.—In this, as in all the other cases,
owing to the water added on the 1st of July, the mass was covered to the depth of from
1 to 2 an inch with fluid. In both the above cases with Wheat, the supernatant water
was colourless, but in this it had a dirty, muddy, yellowish colour. ‘The mass emitted a
foul disagreeable odour, though not so intense as that of the corresponding Barley.

Barley (a)—Seeds, in Soil with 50 cub. cent. water.—The organic matter thoroughly
decomposed ; stems, roots, and leaves no longer distinguishable in the soil; other con-
ditions about as those with the corresponding Wheat a.

Barley (b)—Seeds, in Pumice with 100 cub. cent. water—The pumice covered with a
black coating of organic matter; supernatant water clear. The odour of the air above
the mixture exceedingly disgusting, resembling that of decaying excrements; traces of
sulphide of hydrogen perceptible. The form of the seeds is preserved, but the shell con-
tains only fluid.

Barley (c)—Meal, in Soil with 40 cub. cent. water.—Supernatant water yellowish ;
odour musty, but not very disagreeable. Decomposition so complete that traces of
organic matter are hardly perceptible.

Bean (a)—Seed, in Soil with 50 cub. cent. water.—The organic matter well decom-
posed. Odour musty.

Bean (b)—Seeds, in Pumice with 50 cub. cent. water.—Plants well decomposed ; only
very indefinite skeletons of stems, leaves, and roots remaining. Odour musty, but not
disagreeable.

Bean (c)—Meal, in Soil with 40 cub. cent. water.—Supernatant water slightly yellow.
Odour musty, but not offensive.

The last description, dated August 28, refers to the state of the respective masses just
before being dried for analysis. After drying, any slight remains of organic matter had
become brittle; and the substance, in every case excepting where 100 cub. cent. water
had been added at the commencement, presented the appearance of clean soil or pumice,
without organic matter. In the excepted cases the shell of the grain was still visible.
If we take into consideration the amount of growth in several of the cases on April 28,
it will be seen how great must have been the subsequent decomposition so entirely to
get rid of the organic matter.

It is worthy of remark, that, in a few instances, the sulphuric acid in the bottle D,
fig. 8, Plate I., became coloured slightly brown, indicating the passage into it, through
the oxalic acid, of some carbon-compound more complicated than carbonic acid. In the
course of other parts of our investigation, we have observed phenomena indicative of a
similar result; but as we have not followed up the subject, we leave it with only this
remark as to the fact of what we have observed.

322

506

MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

The following Tables (VIII. and IX.) show the numerical results of the investigation

now under consideration :—

TasLe VIII.—Showing the conditions provided in Experiments on the Decomposition

of Nitrogenous Organic Matter; and the amount and proportion of the original

Carbon of the substance remaining after the decomposition, or given off during the

process.

Substances involved in the Experiment.

Organic Matter.

Weight of
Organic Matter.

Carbon in Organic Matter. |

|
| Before
|

Loss in Decom-

After position.
Matrix. Water. || Fresh. Dry. Decom- | Decom-
Description. Condition. Reith position. quantity Per a
= 7 - 1} = — Ir |

cub. cent. grammes. grammes. ||grammes. grammes. grammes.| |

{ a. 171 seeds ...... Tgnited soil ........ 50 80475 | 67438 || 3:1089 | 09274 || 21815 7017
1, Wheat ...... 6. 171 seeds ...... Ignited pumice...) 100 80715 | 67639 || 31182 | 09178 || 22004 70°56 |
| On ealle rerens canes Ignited soil ........) 40 98810 | 82803 |) 38172 | 13199 | 24973 | 65°42 |
( a. 163 seeds .,.... Ignited soil ........ 50 8:0440 | 67127 || 3:0523 | 09598 | 2-0925 68°55 |
2. Barley ...... b. 163 seeds ...... Ignited pumice ...} 100 81360 | 6:7895 || 3:0872 | 11952 || 18920 | 61-28
| araMleall in. Sraesseese Ignited soil ....... 40 89671 | 74830 | 34025 | 10995 || 23030 | 67°68 |
‘la. 7 seeds Ignited soil ........ 50 5°7830 | 45830 | 22915 | 08511 | 14404 | 62°86 |
3. Beans........4 |. 7 seeds .........| Ignited pumice ...| 59 64700 | 51275 |) 25637 |
CruMloal ivistesenses Ignited soil ........ 40 61750 | 48937 | 24468 | 09778 | 1-4690 60-04 |

Taste [X.—Showing the conditions provided in Experiments on the Decomposition of
Nitrogenous Organic Matter; the amount and proportion of the original Nitrogen

remaining after the decomposition, or given off during the process; together with

the amount evolved as Ammonia, or remaining in the products as such.

Substances involved in the Experiment.

Organic Matter.

Matrix. Water.

Description. | Condition.

a. 171 seeds [Ignited soil ... 50
6. 171 seeds Ignited pumice} 100
lc, Meal «..... Ignited soil ... 40

a. Tgnited soil ... 50
6. 163 seeds |Ignited pumice; 100
lo; Mfeal”s..... Ignited soil ... 40

..\[gnited soil ...
..|[gnited pumice!
Ignited soil ...

cub. cent.

Before
Decom-
position.

Total Nitrogen in Organic Matter.

grammes. grammes.|grammes.

01392
01896
0-1709

01247
01261
01390

0:2417
02704
02581

01398
O-1214
01680

0-0746
01052
01311

02107
02380
02267

0-0501
00209
0:0079

0:0310
00324
00314

| grammes.

Nitrogen in the form of Ammonia,

Absorbed by
Oxalic acid
After iow: Kors Gain). during Decom-
Decom- Total | Per position.
position. quantity.} cent.
Actual Per Actual | Per
quantity.) cent. quantity.| cent.

+0:0006 | + 0-43 | 0-0429
00182} 13-08 || 0-0573
00029; 1-74 || 0.0197

40°20 | 00157
16°62 | 0-0294
566 | 0-0166

12:84 | 0-0140 | 57-91) -00341
MG a ees | Somers “00242
12:16 || 0:1039 | 40:25) -00060

30°83
41-06
1149

grammes.
00038
00002
“00040

“00055
00002
“00039

A comparison of the results in Tables VII. and LX. will show that they are confirma-

tory of each other as to their more general indications.

Both series agree in the entire

absence of any tangible relation between the varied circumstances of decomposition, and

the products of that decomposition.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 507

It is quite evident that, whilst in some instances there has been no evolution of Ni-
trogen, in others the amount of decomposition involving such evolution has been very
great. Indeed, in some cases, the indication of the loss of Nitrogen in this way is so
great that we could not have believed such a result possible had it not been attested by
repeated analysis. But we have not been able to trace these differences to their ulti-
mate causes.

The amount of decomposition, as indicated by the physical condition of the several
substances at the termination of the experiment, as also by the proportion of carbon
given off as shown in Table VIII., might lead to the conclusion that the process had
gone about equally far, and attained about an equal completeness, in all the cases to
which Tables VIII. and IX. refer. But here the equality of effect ceases. Thus, from
60 to 70 per cent. of the total carbon in the original organic matter has passed off; but
the proportion of the original Nitrogen that is not recovered in the products varies,
under the same circumstances, from 0 to 40 per cent. of it. The proportion of the Nitrogen
of the original substance which was retained in the mass, or absorbed in the oxalic acid
in the bulb-apparatus (C) in such form as to be given off as ammonia on distillation
from a weak alkaline solution, and which probably existed, therefore, in the products as
ammonia, ranged from 12 to 58 per cent. of the total quantity involved in the experi-
ment. And, again, the proportion of the Nitrogen evolved from the mass as ammonia
during the decomposition, and which was retained in the oxalic acid solution (C), varied
from 0 to about 1°5 per cent. of the original or total Nitrogen.

If we attempt to trace a relation between the loss of carbon, the loss of nitrogen, the
formation of ammonia, and the evolution of the small amounts of it during the decom-
position, on the one hand, and the circumstances of matrix, moisture, growth, decay,
&c., pointed out in the notes preceding the Tables, we fail to discover any connexion
which we may with safety regard as exhibiting cause and consequence.

The most that we can venture to say is that, under a wide range of circumstances,
a considerable loss of Nitrogen occurs in the decomposition of nitrogenous organic
matter; that under particular, and apparently rather rare circumstances, this loss of
Nitrogen does not occur; that the proportion of the Nitrogen taking, under the same
circumstances, such form that it may be driven off as ammonia on the distillation of the
products with a weak solution of alkali, varied from one-eighth to more than one-half
of the total present; and that the amount of the Nitrogen evolved from the mass as
ammonia during the process was quite inconsiderable.

These conclusions, though necessarily expressed in very general terms, have never-
theless a very important bearing on certain questions in practical agriculture. Whilst
it would appear that there may be a very great loss of Nitrogen—a very important
element in manure—under circumstances of decomposition of organic matter, closely
allied to those to which, in practice, nitrogenous organic manures are subject, it is at
the same time indicated that it is possible for such matters to pass through the process
of decomposition without such loss. 'The importance of further investigation is hence

508 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

suggested, to ascertain the causes of the difference of effect, in order, if possible, to con-
trol them. The results also point to the insignificance of the loss of Nitrogen in the
form of ammonia, a supposed evil to which the attention of agricultural chemists has
specially been directed in order to find means of preventing it, though nothing has as yet
been done to avoid the loss, in apparently much larger quantity, of free Nitrogen. But
as these questions are more appropriate for consideration in a purely agricultural paper,
we shall not follow them further in this place.

Other investigations, to which we have to call attention, will throw some light upon
the character of the molecular forces by which the decomposition of nitrogenous organic
compounds is effected under such circumstances as we have been considering. ‘These
forces might be one or both of two kinds.

1. They might be of an oxidizing character, analogous to that of the action of chlo-
rine upon ammonia by which free Nitrogen is evolved.

2. They might.be of a reducing character, similar to that of a great number of sub-
stances upon the oxygen-compounds of Nitrogen, by which the oxygen of the latter is
appropriated, and free Nitrogen given off.

3. These two actions may operate in succession the one to the other.

It is well known that an oxidizing action may be so intense as to deprive a nitro-
genous organic compound of all its carbon and hydrogen, converting it into oxygen com-
pounds, as is done by permanganic acid. The converse action of the transformation of
oxygen-compounds of Nitrogen into ammonia is also very well known. An intermediate
stage in either of these converse actions may give free Nitrogen.

There can be little doubt that the Nitrogen in the organic substances which we have
submitted to decomposition existed in them in a condition more analogous to a hydro-
gen than to an oxygen compound of it. The able researches of Hormany into the
nature of compounds formed upon the ammonia type, would lead us to suppose that the
Nitrogen compounds upon which we have been operating are of the ammonia class. They
are more difficult to oxidize into nitric acid than is ammonia; yet their transition into
ammonia is so easy, that it is effected in almost all the chemical changes to which they
are ordinarily subjected. And, since ammonias yield free Nitrogen under the influence
of oxidizing forces, it may be inferred that it has been under the influence of such forces
that Nitrogen has been set free in the cases recorded above. PrLouzE has remarked*
that salts of nitric acid are converted into ammonia, in contact with decomposing organic
matter. Experiments of our own have shown that, during the decomposition of organic
matters in contact with nitrates, free Nitrogen is not evolved. The evolution of free
Nitrogen in the experiments quoted above must, therefore, be referred to the action of
oxidizing forces.

The experiments next referred to bear upon these points.

* Comptes Rendus, xliy. p. 118. :

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 509

E.— Experiments on the action of the oxidizing and reducing forces, as manifested

in the decomposition of organic matters containing Nitrogen.

Several qualitative experiments showed that when cereal grains and leguminous
seeds were placed in water, over mercury, an evolution of gas took place, after about
thirty-six to forty-eight hours. This went on rapidly for a week or two, after which
all action appeared to cease, no more gas being evolved. The total quantity of gas
evolved varied between 20 and 50 cub. cent. from 5 to 4 grammes of the seeds. An
examination of the gas proved it to be almost entirely carbonic acid and hydrogen, the
quantity of Nitrogen being very small.

To examine this action more thoroughly, about half a pound of a mixture of Wheat,
Barley, and Beans was taken, put into a long narrow glass vessel (fig. 7, Plate XII.) of
about 500 cub. cent. capacity, which was then filled with well-boiled water, and closed
with a cork, through which two glass tubes (@ and }) passed. The external ends of
these tubes were fitted with caoutchouc tubing, for closing with pinch-cocks, or con-
nexion with the Torricellian exhauster as described at p. 487. One of the tubes being
so connected with the exhauster, it was allowed so to remain for several hours, in order
to remove all the gaseous Nitrogen from the seeds. The vessel was then inverted in
mercury, with one of the tubes (2) open under that fluid, and the whole placed in
sunlight to favour the decomposition. ‘This was done on the 28th of August, 1858.
The seeds commenced swelling very soon, and on the 30th of August well-marked
decomposition had set in.

On September 13th the vessel was about two-thirds full of gas, the displaced water
having passed out through the quicksilver. Part of the seed was now above the water,
in the gas, which commenced bubbling out through the tube (4). The arrangement
was allowed so to remain until October 5, when 400 cub. cent. of gas were collected, of
which the percentage composition was as follows :—

Carbonic acid. Hydrogen. Nitrogen.
Experiment 1. . .. .. [64:87 34°85 0°30
Experiment2 . . . . 64°54 30°46 traces.

The quantity of the gas evolved points to the extent of the decomposition ; the amount
of carbonic acid and hydrogen shows how great must have been the reducing force
exerted ; and the small quantity of Nitrogen, which was probably due to accident,
indicates that free Nitrogen was not a product of the action.

The vessel was again filled with boiled water, again connected for some time with the
Torricellian exhauster, and again placed in its former position in the sunlight.

October 9.—A small bubble of gas collected in the top of the vessel.

November 3.—Only a few bubbles of gas at the top of the vessel.

November 17.—The vessel was removed into the laboratory and placed ina room, ‘the
temperature of which varied from a few degrees above the freezing-point to about 24°C,

December 1.—Very little gas evolved.

December 12.—The gas collected without exhaustion measured only 6-1 cub. cent., of

510 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

which 4:6 were absorbed by potash, and the remainder proved to be combustible.
Hence, up to this date, there has been no appreciable evolution of free Nitrogen. In
order to see whether the organic matter present would reduce a nitrate, with the eyolu-
tion of free Nitrogen, about 5 grammes of saltpetre’ were now put into the vessel, and
it was replaced in the same room as before.

May 8, 1859.—Several times since December 12, 1858, when the nitrate of potash
was put in, the vessel has been warmed up to 30°C.; but up to this date very little gas
has been evolved.

May 25, 1859.—Still very little gas evolved; 4 cub. cent. only collected, one-fourth
of which was carbonic acid, and the remainder was combustible. The vessel was now
placed in the sunlight again, but up to the middle of June no further evolution of gas
had taken place. The fluid still contained nitrate of potash. ‘The vessel was then half
filled with oxygen in order to see if this would cause a renewal of the decomposition.
After ten days a portion of the gas was examined, when it was found that not one-fourth
of the supplied oxygen had been consumed—a result which was quite unexpected. The
total gas being removed, the vessel was again nearly filled with oxygen, driving out the
greater part of the fluid, and leaving the partly decomposed seeds in an atmosphere of
this gas. The apparatus so arranged was placed in the sunlight, and remained there
during some very warm weather.

July 12, 1859.—The gas collected contained in 100 parts—

Carbonic acid. Oxygen. Nitrogen.
20 79 1

By accident a small quantity of air was admitted into the vessel, so that the analysis
can only be taken to show how exceedingly slow was the oxidation of organic matter
which had been treated as this had been.

On the removal of the matters from the vessel, the Beans were found to possess much
of their original firmness and solidity. The other seeds, though they retained their
form, were softer, and they had evidently undergone a more complete decomposition.
They emitted very little odour, which was not unpleasant.

There can be no question as to the absence of any evolution of free Nitrogen during
the long period that these three descriptions of seed were under experiment. A very
small proportion of the combined Nitrogen present would, if set free, have been sufficient
to fill the vessel with gas. But, as has been seen, only a few bubbles of gas were evolved
during several months.

Several other experiments were made upon the products of the decomposition of
organic matter, in the first stages of the process. In Table X., which follows, are given
the amounts, and the composition, of the gas obtained from decomposing organic matter
in a few out of a number of cases in which we have had occasion to observe them—
including, for comparison, some of the results already referred to. The decomposition

took place in water, in vessels similar to that used in the experiments last described
(fig. 7, Plate XII.).

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 511

TABLE X.—Showing the products of the action of the reducing forces exercised in the
decomposition of Nitrogenous organic matter, as exhibited by the composition of
the gases evolved.

| Composition of the Gas, Per Cent.
Description of Organic matter subjected Baie Ses 3 imei
REELS EES Ry Carbonic acid.| Hydrogen. Nitrogen.
cub. cent.
64:87 34°83 0°30
a. Wheat, Barley, and Bean seed ...| 400 64:54 35°46 pescees
6. Turnip plant; root with leaves ...| 166-2 76°23 22:91 0°87
c. Turnip plant; root with leaves ...} 162*2 68-83 23°93 7°24
c : 68-06 25°63 6°31
Pane e tant ts : 236 f
d. Turnip plant; root with leaves ...} 123°6 | 67°52 25:43 7-05
e. Turnip plant; root with leaves...) 41:2 || 64:95 14-66 20°39

The first experiment (a) is that which has been considered above. In all the other
cases about two ounces of young Turnip Plant, the root and leaves together, were
operated upon. They were exposed in similar vessels to those used in the other expe-
riments, from August 29 to October 5. At the termination of this period the structure
of the plant was almost entirely destroyed; and there remained only a mass of decom-
posed matter deposited at the bottom of the vessels. The evolution of gas had entirely
ceased.

The Turnip plant (4) was exhausted of its gas before exposure; and, as will be seen,
there was, under these circumstances, a very small quantity of free Nitrogen found at
the termination of the experiment.

All the other Turnip plants were submitted to decomposition without previous
exhaustion; and hence the amount of Nitrogen eventually found. In the last experi-
ment (¢) there is a much larger percentage of Nitrogen than in the other cases. But
the total quantity of gas was much less; and the comparison of this result with the
others shows that there was an almost constant actual quantity of Nitrogen in the
several cases, doubtless due to that existing within the plant at the commencement of
the experiment. Hence it appears that, in the absence of free oxygen, no free Nitrogen
is evolved from the nitrogenous compounds of the plant.

At all events the entire cessation of the evolution of gas after the decomposition has
gone on for a few days, shows that the presence of free oxygen is essential to the evolu-
tion of Nitrogen, as it is conducive to that of carbonic acid. The loss of Nitrogen
indicated in Tables VII. and TIX. must be considered, therefore, to be the result of an
oxidizing process.

We shall have to allude again to the results given in Table X. when we come to dis-
cuss the question of the formation of ammonia from the free Nitrogen of the air, and
the nascent hydrogen evolved during the decomposition of organic matter.

In order to examine the character of the decomposition of organic matter in oxygen

gas, an investigation was undertaken, which, owing to the difficulty of getting the requi-
MDCCCLXI. 4a

i

512 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

site apparatus sufficiently air-tight, was not followed up to the extent which had been
intended.

The plan proposed was, to place the organic matter in an atmosphere of pure oxygen,
and to afford a constant supply of the gas as it became converted into carbonic acid, and
was absorbed by a solution of caustic potash.

The results obtained go to show that, in the presence of free oxygen, Nitrogen gas is
evolved. But as the investigation is as yet so incomplete, owing to the circumstance
above alluded to, we prefer not to give the results until we can confirm them by a more
extended series of experiments under more fayourable conditions.

Taking together the results of all the experiments which have been made upon the
decomposition of nitrogenous organic matters, they obviously point to a serious difficulty
in the way of experiments made upon the question of the assimilation of free Nitrogen
by plants. It is not possible to conduct any such experiments without exposing nitro-
genous organic matter to conditions more or less analogous to those under which the
loss of Nitrogen recorded in Tables VII. and [X. took place. For although, as Bous-
SINGAULT has shown, there may be no loss of Nitrogen during germination, yet, during
the entire period of the growth of a plant, certain portions of the vegetable substance
may be subjected to conditions favourable to the decomposition of its nitrogenous com-
pounds, and to the evolution of free Nitrogen.

As illustrative of how far these conditions are likely to be operative in the manner
indicated, the following results, made with Wheat, Barley, and Oats respectively, are
very instructive. Seeds of the three plants were sown, each in precisely the same
kind and amount of soil, &c., as employed in the experiments on the assimilation
question. ‘The three pots were placed beneath a large glass shade, 16 inches in diameter,
which fitted into the groove of a stone-ware lute-vessel, into which sulphuric acid was
poured to exclude the access of external air. The whole stood ona table in the diffused
light of the laboratory. The plants were at first supplied with distilled water; but
with no carbonic acid beyond that which might be contained in the water. These con-
ditions afforded all that was necessary for germination and growth, with little oppor-
tunity for the assimilation of free Nitrogen, even were this possible in the more favour-
able conditions of sunlight. Yet the conditions were more than ordinarily favourable
to the decomposition of nitrogenous compounds, provided this would take place, under
certain circumstances, during the growth of the plant. The succulent character of the
stems and leaves so grown in the shade, would render the nitrogenous matters more
able to decomposition than in the case of the more firm and hardened stems of plants
grown in sunlight.

Hight seeds of each plant were sown; and in a few days all came up, and grew very
rapidly in height, without much tendency to development and expansion of leaf. The
plants were all very much alike—tall, slender, delicate, and having the peculiar pale-
green colour common to plants deprived of sufficient sunlight. In several other expe-

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 513

riments it was found that plants which had proceeded for some time in this delicate
form of growth, immediately ceased this predominant upward tendency when removed
into sunlight: then, after remaining stationary for a few days, during which time the
extremities of the long delicate leaves lost their vitality, the plants commenced a new
order of growth, producing many more leaves, which were much shorter and broader
than the earlier ones; the stems also became thicker and more dense than before.

The seeds were put in on May 17 (1858); and on June 10 following, the plants had
ceased to grow. Several of the long slender stems were too delicate to support them-
selves, and began to fall over. All the plants presented much the same appearance,
each with a small sheath without any leaf at the base, and three leaves higher up—the
two lateral ones being very long, from 8 to 12 inches, and the terminal ones, not unrolled,
from 3 to 4 inches long from the axial of the next leaf below, the whole plant being from
7 to 1l or 12 inches high. On removing them from the soil, it was found that the roots
were distributed very little through it. They consisted of short fibrils, with divaricated
branchlets, extending principally around the seeds, and seldom more than 2 or 3 inches
through the soil. The plants were so very much alike, that it was difficult to distinguish
the different kinds. Fig. 9, Plate XII., is reduced from a sketch of one of these atten-
uated plants.

The following Table gives the quantitative particulars of the experiments.

TasLeE XI.—Showing the effect of Germination, and Growth without direct Sun-light,
or extraneous supply of Carbonic Acid or combined Nitrogen, upon the combined
Nitrogen originally provided in the Seed.

Duration of experiment twenty-four days—from May 17 to June 10, 1858.

Particulars of the seed sown. Nitrogen.

Dry vegetable matter
produced.

PEt ori :
Total. In stems | In soil || In total Gain or

Weight, | Weight,
° jand roots.| and pot. | products. loss.

Description. | No. Frente dry.

weal Stems. | Roots.

|
gramme. | gramme. |} gramme, | gramme. | gramme, | gramme. | gramme. | gramme. gramme, gramme.

Wheat ...... 8 | 04865 | 04077 || 0:00790 | 0:320 0-140 0-460 0:00697 | 0:0012 000817 | +-0:00027
Barley ...,.. 8 | 03875 | 0:3234 || 000573 || 0-290 0-160 0-450 000570 traces 0:00570 | —0:000038
Ontatecsncrs. 8 | 03475 | 0-2900 || 0-00640 | 0:355 0-060 0-415 0:00640 traces 0:00640 | + traces

The weights given for the roots are a little too high, owing to their not having been
washed entirely free from soil, the principal object being to ensure a correct result with
regard to the Nitrogen which long washing might have endangered, or at least rendered
less easy. ‘There is, however, evidently a slight gain of dry matter, which, so far as its
carbon is concerned, was doubtless due to carbonic acid in the distilled water, of which
about 500 cub. cent. were added to each pot at the commencement of the experiment.
None was added during the progress of the experiment; but the soil was moist when
the plants were taken up.

The rapid growth of the plants, the short period of their contact with the soil, the

442

514 MR. J. B. LAWES, DR. GILBERT, AND DR, PUGH ON

very limited distribution of the roots, and the fact that no water was added during
growth, which would tend to distribute any soluble or otherwise easily transportable
matters, are conditions all consistent with the almost total absence of Nitrogen in the
soil.

Lastly in regard to the results in the Table (XI.), the final column, showing the gain
or loss of Nitrogen, affords us the means of judging how far the molecular actions by
which free Nitrogen was given off in the cases of the experiments upon the decom-
position of nitrogenous organic matter are likely to interfere with the results of our
investigations on the question of assimilation of free Nitrogen by plants. It is seen that,
in the experiments now under consideration, no free Nitrogen was given off during the
process of germination and growth. At least, the assumption that free Nitrogen was
given off implies the still more improbable one, that, under the circumstances detailed,
assimilation of free Nitrogen has taken place; whilst the adoption of these two assump-
tions necessitates the yet more improbable one, that these two independent actions bear
a most definite relation to each other—in fact, that the amount of free Nitrogen
assimilated is exactly equal to that given off during decomposition.

It would appear, therefore, that we way rest satisfied that our results in regard_to the
question of assimilation will not be affected by a loss of free Nitrogen as the result of
the decomposition of nitrogenous organic matter, so long as that matter is subjected to
the ordinary process of germination, and exhaustion to supply materials for growth.
Our results in regard to the products of decomposition of nitrogenous organic matter do,
indeed, point to the danger of using nitrogenous organic manure in such experiments, and
to the error that might occur from seeds decomposing in the soil instead of growing, or
from the decomposition of dead leaves, of old roots, or of nitrogenous organic excretions ;
but they do not afford any evidence of what takes place within the range of the action
of the living plant. And, judging from the amount of free Nitrogen evolved when, as
in the experiments on decomposition, so large a proportion of the nitrogenous organic
matter was decomposed, we may form some idea of the probable extent of such eyvolu-
tion when, as in experiments where vegetable growth is involved, and where the only
nitrogenous organic matter supplied is that in the seed sown, but a small proportion of
the total nitrogenous matter undergoes decomposition.

In relation to this question, it should be borne in mind that, in the cases where the
large evolution of free Nitrogen took place, the organic substances were subjected to
decomposition for a period of about six months, during which time they lost three-fourths
of theircarbon. In the experiments on the question of the assimilation of free Nitrogen,
however, but a very small proportion of the total organic matter is subjected to decom-
posing actions apart from those associated with growth, and this for a comparatively
short period of time, at the termination of which the organic form is retained, and
therefore but little carbon is lost. It would appear, then, that we need not fear any
serious error in our experiments in regard to the latter question, arising from the
evolution of free Nitrogen in the decomposition of the nitrogenous organic matters

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 515

involved. On the other hand, the facts adduced afford a probable explanation of any
small loss of Nitrogen which may occur when seeds have not grown, or when leaves, or
other dead matter, have suffered partial decomposition.

F.—The mutual relations of Gaseous Nitrogen and the Nascent Hydrogen evolved during
the decomposition of organic matter.

The importance attached by MuupEr, and others after him, to the action of nascent
hydrogen, evolved in the decomposition of organic matter, upon gaseous Nitrogen, as a
source of ammonia, is such as to require that we should refer to the subject here, in
the course of the discussion of the conditions possibly affecting the supply of combined
Nitrogen to our experimental plants. The results given in the last sub-section (pp. 509—
511), leave no doubt of the evolution of hydrogen during the decomposition of organic
matter. They suggest, therefore, the possibility that such an evolution may take place
in any decomposition of organic matter involved in our experiments on the assimilation
of free Nitrogen by plants, and hence prove a source of ammonia to them.

That nascent hydrogen may, under certain circumstances, combine with gaseous
Nitrogen, has long been admitted. But the view so prominently put forth by MuLpEr*,
and some others, that those circumstances occur in the evolution of nascent hydrogen
accompanying the decomposition of organic matter, requires confirmation.

If only a very small part of the hydrogen evolved in the decomposition of organic matter
were to form ammonia with the Nitrogen gas which must always be in most intimate con-
tact with it, the amount of ammonia formed in this way would be enormous. Peat bogs,
cesspools, and all stagnant water pregnant with organic matter, as well as many soils,
would be constantly so accumulating ammonia. ‘The extensive forests in different parts
of the world, which have been annually depositing a coating of leaves upon the surface
of the soil for thousands of years, must also have been a very fertile source of ammonia,
as the leaves have gradually decayed under the influence of moisture and confined air
beneath the succeeding layers. And when we contemplate the amount of decomposi-
tion that must have corresponded to the very exuberant growth of former geological
periods, as manifested in the remains exhibited in our coal beds and limestones, we see
a source of ammonia, if formed in the manner now under consideration, which would
be incalculable.

The results given in the last subsection (E), upon the decomposition of nitrogenous
organic matter, favour the view that the hydrogen evolved in such decomposition does
not form ammonia with the Nitrogen of the air. The assumption that it did so, implies
that the nascent hydrogen was capable of uniting with free gaseous Nitrogen (forming
ammonia) under circumstances in which its affinities were not sufficiently powerful to
prevent Nitrogen compounds very similar to ammonias (and which are easily transformed
into them) from giving up Nitrogen in the free state. It implies also, that the nascent
hydrogen can act upon ordinary Nitrogen, when it cannot do so upon this nascent Nitro-

* Chemistry of Vegetable and Animal Physiology, pp. 111-114, 149-152, &e.

516 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

gen of the decomposing nitrogenous body. Or, if it did act upon the latter in preference
to the former, there would either be no free Nitrogen finally evolyed, or, in case of Ni-
trogen being lost in the free state, it would be obvious that there had been less nascent
Nitrogen converted into ammonia than had been liberated from its combinations, and
hence that, as a resultant, there would be a loss and not a gain of combined Nitrogen
due to the decomposition.

The fact that, in our experiments upon the gas evolved by vegetable matters in a state
of decomposition, both free Nitrogen and free hydrogen were given off, bears strongly
upon this question. The Nitrogen evolved has been in most intimate contact with the
hydrogen given off. It has, indeed, been in the identical cells by the decomposition of
the walls or contents of which the hydrogen was set free; yet both appear as gas.

From the above considerations it would appear that we need be under little appre-
hension of error in the results of our experiments on the question of the assimilation
of free Nitrogen by plants, arising from an unaccounted supply of ammonia formed under
the influence of nascent hydrogen, given off in any decomposition of the organic matter
involved in the experiment.

Summary Statement of the Results of the foregoing consideration of the conditions required,
or involved, in Experiments on the question of the assimilation of free Nitrogen by
Plants.

Before entering upon the discussion of the results of our direct experiments upon the
question whether or not plants assimilate free Nitrogen, it will be well, for the sake of
perspicuity, to give a very brief enumeration of the results arrived at in the foregoing
Sections I. and II. (Part II.), relating to the conditions of experiment required, and to
the collateral investigations involved, in the inquiry. They may be stated as follow :—

1. Conditions of soil or matrix which are both adapted for healthy growth and are
consistent with the other requirements of the investigation can be attained (Section I.
Sub-sections A, p. 470, and L, p. 484).

2. The requirements of the experiment in regard to the selection of seeds or plants
for growth, to the nutriment to be supplied in the soil, to the water, to the atmosphere,
to the carbonic acid, and to other conditions involved, can be satisfactorily met (Sec-
tion I. Sub-sections B—J, inclusive, pp. 472-481; and L, p. 484).

3. The conditions of experiment adopted have several advantages over some of those
which have been suggested, or adopted, by others (Section I. Sub-section K, pp. 481—
483).

4, The mutual actions of the soil, air, organic matter in the soil or in the plant, are
not such as to be likely to affect the result of the experiment, by yielding to the plants
a quantity of combined Nitrogen not taken into account. The influence of Ozone as a
possible element in these actions would be less, in the circumstances of the experiments

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 517

on ssimilation, than in those of experiments the results of which showed no appreciable
formation of compounds of Nitrogen (Section IT. Sub-sections A-C, pp. 484-497),

5. The fact of the evolution of free Nitrogen during the decomposition of nitro-
genous organic matter has been confirmed by experiment; but the circumstances of the
decomposition in which the evolution of free Nitrogen was observed, when compared
with those involved in an experiment on the question of assimilation, are not such
as to lead to the conclusion that there would be a loss of Nitrogen from this source in
experiments of the latter kind, unless in certain exceptional cases, in which it might be
presupposed (Section II. Sub-section D, pp. 497-508).

6. The forces, by virtue of which free Nitrogen is eliminated from its compounds in
organic matter, are of an oxidizing character; they are not exercised in the absence of
oxygen. ‘They are not likely to be operative in connexion with growing vegetable
matter (Section IT. Sub-section E, pp. 950, 951).

7. Although it is known that, under certain circumstances, nascent hydrogen may
combine with free Nitrogen and form ammonia, it is questionable whether the nascent
hydrogen eliminated during the decomposition of vegetable matter will be in the con-
ditions to effect such a combination; nor are the circumstances of our experiments on
the question of the assimilation of free Nitrogen by plants such as to lead to the sup-
position, that an error in the results can arise from the formation of any ammonia under
the influence of the action supposed (Section II. Sub-section F, pp. 515, 516).

Szorron I1I.—CONDITIONS OF GROWTH UNDER WHICH ASSIMILATION OF FREE
NITROGEN BY PLANTS IS MOST LIKELY TO TAKE PLACE; DIRECT EXPERI-
MENTS UPON THE QUESTION UNDER VARIOUS CIRCUMSTANCES OF GROWTH.

A.—General consideration of conditions of growth.

We have thus far discussed, in some detail, the arrangement adopted in our experi-
ments on the question of the assimilation of free Nitrogen by plants, and the colla-
teral points involved in the relation of gaseous Nitrogen to vegetation. In regard to
the latter, we have dwelt particularly on those which relate to the sources of avail-
able Nitrogen to plants, and which, therefore, may tend to influence the quantitative
results which we may obtain by the methods of experimenting followed. It remains
to consider what are the circumstances under which it is most probable that free
Nitrogen may be assimilated, provided the assimilation can take place at all.

The demonstration of the fact, that the process of cell-development could go on in
the presence of free Nitrogen without the latter becoming incorporated into the cell
wall, or into the contents of the cell, as a nitrogenous compound, would not carry with
it the demonstration that free Nitrogen could, under no conditions of growth, undergo
such change. Our aim should be, therefore, to seek the most probable circumstances

518 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

for such change; and if we find that in them free Nitrogen is assimilated, we should
then trace up the question through the circumstances in which such assimilation is less
likely to take place.

If, on the contrary, we find that free Nitrogen is not assimilated under the cireum-
stances which appear the most favourable for such an action, we may either generalize
for other conditions from the negative results so obtained, or we may extend our experi-
ments in order to widen the basis of our generalizations.

In the consideration of what are the cases in which the assimilation of free Nitrogen
is most likely to take place, two important classes of conditions present themselves :—

1. Those which relate to the supply of combined Nitrogen at the disposal of the
plant.

2. Those which relate to the activity of growth and stage of development of the
plant.

These two questions, though logically distinct, are physiologically blended ; for it may
happen that a certain activity of growth, or certain stages of development, can only be
attained by a given supply of combined Nitrogen beyond that contained in the seed.

If we examine these conditions a little more closely, we see that they give us the
following possible cases for the assimilation of free Nitrogen by the plant :—

1. The plant may be able, in the process of cell-formation, to derive the whole of its
Nitrogen from that presented to it in the free state.

2. It may be capable of assimilating a part of its Nitrogen from that presented to it
in the free state, provided it be supplied with only a part of its required amount in some
form of combination.

3. It may assimilate free Nitrogen in the presence of an excess of combined Nitrogen.

Again :—

1. It may be capable of assimilating free Nitrogen in the earlier stages of its develop-
ment.

2. It may be so at the most active period of its growth.

3. It may when near the period of its maturity.

Combinations of these several circumstances present at least nine special cases, in one
of which, if at all, an assimilation of free Nitrogen might take place without its doing
so in any of the others. The question arises, how are we so to arrange our experiments
as to include the greatest number of these cases, and those in which the assimilation of
free Nitrogen is the most likely to occur?

The obviously most probable circumstances for the assimilation of free Nitrogen at
any stage of development of the plant, are those in which it is brought to that stage in
a healthy condition, and then deprived of all sources of combined Nitrogen. It is
hardly to be supposed that an assimilation of free Nitrogen would take place if there
were an excess of combined Nitrogen at the disposal of the plant; for, if we suppose
that the molecular and vital forces are at the same time acting upon Nitrogen supplied
by these two sources, in a manner tending to force that from both into the constitution

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 519

of the living organism, it is only consistent with our established notions of force, that
the form which yields with the greatest ease will yield first, and that, if its supplies be
in sufficient quantity, it only will yield in an appreciable degree to the force applied.

If, on the other hand, the forces involved in vegetable growth, tending to form nitro-
genous compounds, are capable of appropriating free Nitrogen only in the presence of a
certain amount of assimilable combined Nitrogen, then the question of deciding upon
the proper proportion of combined Nitrogen to effect the assimilation of that provided
in the free state would seem, & priori, to present serious difficulty. For if the plant
cannot assimilate free Nitrogen either in the presence of an excess of combined Nitro-
gen, or without the aid of a certain amount of it, it would, at first sight, appear that
there might be some difficulty in so arranging an experiment as to hit the proper
medium.

But within a certain range of conditions this supposed difficulty would not occur. If
the assimilation of free Nitrogen be possible only as the result of the assimilating forces
acting upon it in the presence, or with the aid, of a certain amount of combined Nitro-
gen, then, when the quantity of combined Nitrogen has become too small, the point
must have been passed at which the maximum amount of free Nitrogen would be assi-
milated in relation to the then existing supply of combined Nitrogen. Hence, the
analysis of a.plant at the period at which its growth ceased in consequence of the falling
short of the relative supply of Nitrogen in the combined form, would show whether or
not an assimilation of free Nitrogen had taken place as the result of either of the con-
ditions referred to in the last paragraph.

If, however, the plant cannot assimilate free Nitrogen under the conditions of the
supply of combined Nitrogen just referred to, unless it has attained a certain vigour of
growth, or reached a certain stage of its development, and the supply of combined
Nitrogen has been insufficient to bring it to the supposed requisite point, then no
assimilation of Nitrogen would take place, even though it might do so provided the
proper stage of growth had been passed. To the cases here supposed we shall recur
further on.

If the assimilation of free Nitrogen can take place at all periods of the growth of the
plant, and in the absence of all sources of combined Nitrogen, the solution of our ques-
tion becomes much more simple than in either of the cases above referred to.

In illustration of the fact that, within a certain range of other conditions, there can
be no difficulty in securing in an experiment those involved in the presence of an excess,
of a certain limited quantity, or of no combined Nitrogen, attention may be directed
to the phenomena of vegetable growth when seeds are grown in a soil and atmosphere
free from combined Nitrogen.

Under the circumstances supposed, all the conditions with regard simply to the rela-
tive quantity of combined Nitrogen are afforded. Thus, when the seed is first sown, it
contains within itself an excess of combined Nitrogen, so far as the demands of the
plant at the time are concerned. The rapidity with which the Nitrogen of the seed can

MDCCCLXI. 4B

520 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

be used, in the growing process, is seen in the results of the experiment in regard to the
question of the decomposition of Nitrogenous matter during growth, as given in Table
XI. (p.513); and the extent to which it can carry the growth of the plant is illustrated
in that experiment, as well as in others, to which we shall presently refer, relating to the
question of assimilation itself. It is obvious that, during a part of the time at the end
of which the plant has reached the limit of its supply of combined Nitrogen, it has had
at its disposal an excess of combined Nitrogen for its immediate wants. It has then
passed through a stage in which the particular relation of combined to free Nitrogen
implied in another of our assumed conditions must have existed. It must finally have
reached a point at which only free Nitrogen was presented to it.

If an analysis of the plant at the termination of the last-mentioned period showed no
increase of Nitrogen, the result would afford conclusive evidence against the possibility
of the assimilation of free Nitrogen under a wide range of conditions. If, on the con-
trary, a gain of Nitrogen were indicated, the question would still be open, to which
of the several conditions to which the plant had been subjected it owed the increase
found. But this question we need not discuss until we have recorded the results of our
experiments on the point.

B.—Direct experiments on the question of the assimilation of free Nitrogen by plants.

We have thus far discussed the methods of experimenting to be adopted, the results
of certain collateral inquiries, and the several conditions under which the assimilation of
free Nitrogen by plants may be the more or the less likely to take place. We have thus
endeavoured to eliminate all known sources of error, and to acquire the means of form-
ing an estimate of the possible influence of certain unknown quantities, and so, as far as
practicable, to reduce the solution of our question to that of a single point to be tested
by direct experiment. It remains to consider the experimental evidence relating to
this last and final point.

An investigation requiring several hundred analyses, and a series of observations made
at intervals of a few days, through periods of several months, involves an amount of
recorded detail much too voluminous for full publication. An abstract of the most
important portions of the records will, however, be given for reference in the Appendix.
A statement of the methods of analysis adopted, with illustrations of the limits of accu-
racy reached, together with a condensed summary of the details of growth of the plants,
will there be given.

In the selection of the plants to submit to our adopted conditions of experiment, we
have been guided by several considerations :—

1. To have such as would be adapted to the conditions of temperature, moisture, &c.,
to which they were to be subjected.

2. To have such as were of importance in an agricultural point of view.

3. To acquire the means of studying any difference, in reference to the point in
question, between plants which belong respectively to the two great Natural Orders

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 621

~_

the Graminacee and the Leguminose, which, in some points of view, appear to differ
so widely in their demands upon combined N itrogen provided within the soil.

4. To take such as had already been experimented upon, with such conflicting results,
by M. Boussryeauut and M. G. Vite.

We shall first consider the results obtained with plants grown without any other
supply of combined Nitrogen than that contained in the seed sown.

1.— Experiments in which the plants had no other supply of combined Nitrogen than
that contained in the seed sown.

The following Table (XII.) gives, at one view, a summary of the numerical results
obtained under this head; see also figs. 1-6, Plate XV., which are reduced from careful
drawings taken of six out of the nine Graminacee experimented upon, and illustrate
the character and extent of growth attained under the conditions in question.

After the full discussion in the foregoing pages of the circumstances under which the
results recorded in the Table just given were obtained, but little need be said in pointing
out their bearings upon the question at issue. The column showing the gain or loss in
each experiment speaks for itself. In judging of the results of the experiments of
1857, the remarks made in discussing the results of Table XIV. (p. 532), with regard
to the slates used as lute-vessels in that year, must be taken into consideration. The
source of error referred to being obviated in the experiments of 1858, the results of 1857
acquire a greater value, as confirming those of the latter year, than, standing alone, they
would possess.

The difference between the results obtained with soil and with pumice as matrix, in
1857, are not such as to lead us to attach any importance to them, or to attribute them
in any way to the difference of matrix in question. The two experiments may there-
fore simply be considered as duplicates. Indeed, the character of the results in the one
experiment with Wheat, and in the two with Barley, in 1857, was so similar, that the
three experiments may be considered as triplicates.

Graminaceous Plants.

It will be observed that the largest gain of Nitrogen in the three experiments with
Graminacee in 1857 was 0-0026 gramme. Keeping in view the probable source of
error due to the use of slates in that year, and the difference of result in 1858 when
slates were not employed, and, again, considering the fact that so small an amount of
Nitrogen had to be determined in such a large amount of soil (0-003 gramme or less of
Nitrogen in about 1500 grammes of soil), it seems indeed more than questionable whether
the gain should not be attributed to the errors of experiment or analysis alluded to. In
fact, we can but conclude that, under the circumstances of growth of the Graminaceous
plants to which Table XII. relates, there has been no assimilation of free Nitrogen.

It should also be noticed that, even when a gain of Nitrogen in the total products is
observed, there is, in no case, more Nitrogen in the plant itself than in the original

4B2

MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

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THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 525

seed,—the gain appearing only when the Nitrogen in the soil and pot is taken into
account. It will be remembered that the results of the experiments on the question
whether there was an evolution of Nitrogen during germination and growth (Table XI.,
p- 513) showed how completely the plants could appropriate the Nitrogen of the seed
from which they grew, leaving only traces of it in the soil. Again, the experiments on
the decomposition of Nitrogenous organic matter (Tables VIII. and IX., p. 506) have
shown how thorough was the decomposition coincident with the passage of any large
percentage of the combined Nitrogen of the substance into the soluble state of ammonia.
Taking together these facts, we have strong grounds for assuming that at least a part
of the Nitrogen found in the soil, in the cases where there was a gain of it in the total
products, has never been in actual connexion with the plant at all. Indeed, in view of
the facts just referred to, any gain of Nitrogen in connexion with the plant, without
there being a larger quantity of Nitrogen in the plant itself than that provided in the
seed, would be very questionable evidence upon which to establish the fact of the assi-
milation of free Nitrogen.

But the results obtained with Graminacee in 1858, when all possible sources of error
which the experience of the previous year had suggested had been eliminated, point,
without exception, to the fact that, under the circumstances of growth to which the plants
were subjected, no assimilation of free Nitrogen has taken place. The regular process
of cell-formation has gone on; carbonic acid has been decomposed, and carbon and the
elements of water have been transformed into cellulose; the plants have drawn the nitro-
genous compounds from the older cells to perform the mysterious office of the formation
of new cells (see Notes on growth, Appendix, pp. 559, 561); those parts have been deve-
loped which required the smallest amount of Nitrogen; and all the stages of growth
have been passed through to the formation of glumes, pales, and awns for the seed.
In fact, the plants have performed all the functions that it is possible for a plant to
perform when deprived of a sufficient supply of combined Nitrogen. They have gone
on thus increasing their organic constituents with one constant amount of combined
Nitrogen, until the percentage of that element in the vegetable matter is far below the
ordinary amount of it—that is, until the composition indicates that further development
had ceased for want of a supply of available Nitrogen.

Throughout all these phases, water saturated with free Nitrogen has been passing
through the plant; nitrogen dissolved in the fluid of the cells has constantly been in
the most intimate contact with the contents of the cells and with the cell-walls. The
newly forming cell, stunted in its development for want of assimilable Nitrogen, has
nevertheless been surrounded by free Nitrogen, Its delicate membranes have been
saturated with water, itself saturated with free Nitrogen; and such are the laws in
accordance with which the absorption of gases, and the transmission of liquids through
membranes take place, that the instant a part of the Nitrogen of the saturated fluid be-
came assimilated, the equilibrium would be restored, by the penetration into the cell of
other saturated liquid, and the re-saturation of that from which Nitrogen had been with-

524 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

drawn. It would hardly be supposed that, under such circumstances, the process of
cell-formation could go on without the assimilation of free Nitrogen, provided any forces
were exerted in the cell the tendency of which was to fix free Nitrogen in the organism
of the plant.

One fact, briefly alluded to above, we wish to call more special attention to, as afford-
ing strong evidence of the absence of the power on the part of these cereal plants to
appropriate free Nitrogen—namely, the very large development of the root, requiring
but little Nitrogen compared with that of other parts. It was observed, in the expe-
riments of 1857, that several of the cereal plants developed a large proportion of root;
but the danger of accident in analysis was such, that we hesitated to double the risk of
losing the entire result by analysing the root and the portion of the plant above ground
separately. They were, therefore, thoroughly mixed, and the mixture was carefully
divided ; so that, in case of accident, a duplicate was at our disposal, and in case of all
going well, confirmatory evidence was obtained. So very marked, however, was the
great development of root in the cereals of 1858, that, in several cases, it was analysed
separately from the other parts of the plant. The remarkable result was obtained, that
this great root-development was carried on (in two, at least, out of the three instances in
question) with a consumption of an almost incredibly small amount of Nitrogen, as the
figures given in the following Table will show :—

TABLE XIII.

tae PON ee | Nitrogen in Produce (grammes). || Per cent. Par cent,
qc of Total | of Total
Description of Plant. | Dry Matter! witeoen
|| In Stems, | 7, Roots, || Im Total || In Stems, | 7, Roots, | Im Total | in Roots. a tae
1858. &e. | Produce. &e. “|| Produce. | a

! ogee, | |
Wheati(l))).- 42-2. | 0°890 0°850 | 1-740 00039 | 0:0017 0-0056 48°85 | 30°36
Barley (2) ......... | 0-400 | 0-160 | 0-560 | 0-:0027 | 00004 0-003) 28°57 | 12:90
ats #4(3)\eteecees | 0-798 | 0350 | 1148 | 0:0040 | 0:0002 0:0042 30-49 | 4-76

The large ee of x root and its small proportion of Nitrogen, as here exhibited,
are equally remarkable. Whether this great power of the plant to develop root be due
to the fact that the process of cell-formation in the root requires less of the nitrogenous
protoplasmic compound, or to the fact that, floating in water as these roots generally
were, that fluid facilitated the withdrawal of the nitrogenous constituents resulting from
the decomposition of protoplasma from the old cells, to form new protoplasma for the
more active cells, is a question which, though foreign to our present subject, is of con-
siderable interest in a physiological point of view. ‘The fact that the roots from the
base of the stem penetrated the soil, giving off very few branches into it, but immedi-
ately on reaching the water at the bottom of the pot exhibited such a remarkable deve-
lopment (see Notes on taking up the Wheat Plants, Appendix, p. 560), is in favour
of the inference that the water afforded the necessary conditions for the character of
growth referred to.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 525

But, apart from the physiological points just referred to, as already said, this great
development of a part of the plant requiring a minimum amount of Nitrogen affords
strong evidence of its inability to assimilate free Nitrogen within the range of develop-
ment possible when no combined Nitrogen is provided beyond that contained in the
original seed. It exhibits the great tenacity of growth of the plant, and shows the
activity of the vital force, long after the demands of the organism had begun to require
more available Nitrogen than was at its disposal. When it is considered how great was
the length of time during which the growing cells were exposed to the conditions in
question, there would seem to be a combination of circumstances favourable to the
exercise of any force tending to bring free Nitrogen into the constitution of the plant.
But no such effect is manifested in the results.

The Graminacee referred to in the Table (XII.) under the Title of “1858, A.,” and
which were grown in the enclosing apparatus of M. G. Vin, as already alluded to, give
results quite similar in their bearings on the main question to those of 1857 and 1858
already discussed. Being sown later, however, and their period of growth being shorter,
they did not manifest such an extraordinary development of root; nor was there so
large an amount of vegetable matter produced. Unfortunately the barley grown in
M. Viute’s Case without artificial supply of combined Nitrogen, was lost by the giving
way of the tube in the combustion for the determination of Nitrogen. In its case,
therefore, we can only give the amount of the dry matter of the plants produced. But,
comparing this with that of the seed sown, and looking to the proportions of Nitrogen
in the produce of barley in the other cases, there is no reason to believe that the result
would have formed any exception to that indicated in the other experiments.

In concluding our remarks on the results with the Graminacee grown without any
further supply of combined Nitrogen than that contained in the seed sown, we would
beg to refer the reader to the foregoing consideration of the conditions possibly favour-
able to the assimilation of free Nitrogen (p. 517 et seq.).

It will be remembered that, in experimenting with Graminacee, including some of the
same description as those experimented upon by ourselves, M. Bousstncautt and
M. G. VILLE obtained most unaccountably discordant results. It will be seen that our
own results, from nine experiments with such plants, go to confirm those of M. Boussin-
Gautt. In fact, so far as our labours with these plants bear upon their experiments,
they could not have given a more decided result.

For representations of some of the Graminacee grown without any supply of com-
bined Nitrogen beyond that contained in the original seed, see figs. 1 to 6, Plate XV.

Leguminous Plants.

It still remains to consider the results of our experiments with Leguminous plants
grown under similar conditions to those of the Graminaceous ones above discussed, and to
see how far they serve to explain the known characteristics of such plants when grown in
practical agriculture, to which attention has been directed in Part First of this Paper.

526 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

It will be remembered that, under equal circumstances of soil and season, Leguminous
crops yield two, three, or more times as much Nitrogen per acre as Graminaceous ones.
Yet, whilst the latter are very characteristically benefited by the use of direct nitro-
genous manures, the former, yielding so much more Nitrogen, are not so. Again, the
Graminaccous crop, requiring for full produce such direct supply of available Nitrogen
within the soil, is very much increased, beyond what it would be if it succeeded a crop
of the same description, when it follows a Leguminous crop, in which has been carried
off so much Nitrogen.

Experiments such as those now specially under consideration can obviously bear
upon a few only of the circumstances with which may be connected the causes of this
difference between the Graminaceous and the Leguminous crops. Without, therefore,
pretending adequately to discuss this wide subject, we will consider it only so far as our
immediate facts appear to bear upon it; they seem to limit us to the consideration of
the following cases :—

1. The difference may be due to the decomposition of nitrogenous compounds during
the growth of the Graminaceous plants, and to the evolution of free Nitrogen.

2. The Leguminous plants may assimilate the free Nitrogen of the air, and thus, not
only allow the resources of the soil to accumulate, but also leave within it an additional
quantity, in roots and other vegetable débris, from that which has been assimilated, as
above supposed.

5. It may be due to the operation of both these causes.

So far as the facts we have already considered go, the difference in question cannot
be explained according to the first of the above suppositions; and others, to which we
shall have presently to refer, will be seen to afford confirmatory evidence on the point.

With regard to the second supposed explanation, the results we have now to record
of our experiments with Leguminous plants are not of themselves sufficient to settle
every point which it involves. Reference to the Appendix will show that, in several
cases, we failed to get healthy growth with Leguminous plants. A doubt might hence
be raised, as to the value of those experiments in which we were successful under
circumstances so nearly identical with those of our failures that it was not easy to
account for the difference of result obtained. In those cases, however, in which we
have succeeded in getting Leguminous plants to grow pretty healthily for a consider-
able length of time, the results, so far as they go, confirm those obtained with
Graminacee, not showing in their case, any more than with the latter, an assimilation
of free Nitrogen.

In 1857, we commenced several experiments with beans, but they grew well in
only one of the shades. These, however (especially one plant out of the two in the
same pot), progressed remarkably well for a period of 10 weeks, during which time the
amount of carbon was increased five-fold, more than three-fourths of the total Nitrogen
of the seed was appropriated, and the plants probably only ceased to grow when the
remainder of the latter became so distributed in the soil as not to be available to them.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 527

A reference to Table XII. will show the numerical results of this experiment with
beans in 1857.

The beans and peas of 1858, the particulars of which are also given in Table XII,
did not grow so satisfactorily as the beans of 1857, last noticed. Yet the beans of
1858 gave more than three times as much organic matter in the produce as was con-
tained in the seed, and they appropriated even a much larger proportion of the Nitrogen
of the seed than did those of 1857. The result with the peas was not so satisfactory,
owing to the less healthy character and the more limited amount of their growth.

From the fact that these Leguminous plants did not go through a complete course of
growth to the flowering process, it may be objected that hence they did not pass certain
stages of growth in which they might possibly assimilate free Nitrogen. We shall refer
to this objection again further on. At present we confine attention to the important
fact, that active growth has taken place—that the process of cell-formation, with the
accompanying one of the decomposition of carbonic acid and the fixation of carbon, has
gone forward with a deficient supply of combined Nitrogen, and in the immediate pre-
sence of free Nitrogen, and yet none of it has been assimilated. The plants have in fact
been subjected to a considerable range of the conditions which were considered, @ prior?,
to be favourable to the assimilation of free Nitrogen; and yet this has not taken place.

It is a fact observed in agriculture, that manures rich in organic matter frequently
favour the growth of Leguminous crops. We shall not here discuss the question
whether these organic manures, as such, act simply as a source of carbonic acid, or of
carbon compounds of a more complicated character. We would, however, call attention
to the fact that, in the case of the experiments now under consideration, the vital forces
were sufficiently energetic to perform the function of cell-development and multiplica-
tion, from carbonic acid as its source of carbon; yet these forces, capable of effecting
this result, have been incapable of effecting the appropriation of free Nitrogen,

Buckwheat.

The evidence afforded by the numerical results in the Table XII. relating to this
plant is not of so decisive a character as that with regard to the cereals, or even to the
Leguminous plants; for the quantity of dry matter in the produced plants is less than
that in the seed sown, whilst the Nitrogen in the plants is little more than one-third
that of the seed. But when we come to compare the results of the experiments with
Buckwheat grown with and without the supply of ammonia, it will be found that the
physiological evidence of the dependence of vegetable growth upon a constant supply of
combined Nitrogen is stronger in the case of these plants than in that of the cereals.
The small proportion of the total Nitrogen of the seeds which the buckwheat seemed
capable: of appropriating might lead to the inference that, ceasing to grow with an
abundance of combined Nitrogen apparently at its disposal, it had done so for some
other reason than the want of available Nitrogen. But this question was set at rest by
the fact that, on the addition of an amount of ammonia very small in its contents of

MDCCCLXI. 4c

528 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

Nitrogen compared with the seed, to plants at the time in a precisely similar con-
dition to those now under consideration, the increase in the rapidity of growth was most
marked.

Most of the buckwheat seed sown came up; but about half of the plants lived for only
a few days. The remainder, which survived, went through all the stages of develop-
ment to flowering; but the entire amount of growth was on a very limited scale.

Reference to the last column of Table XII. will show that, under the conditions of
growth above described, the buckwheat, like the plants already discussed, indicated
no gain of Nitrogen. In fact there appeared to be a loss in the experiment of nearly
2 milligrammes of Nitrogen; and that the result should be to a small extent in this
direction may, perhaps, be accounted for by the fact of some of the plants dying early,
in consequence of which there may have been a slight evolution of free Nitrogen due
to decomposition.

Bearing of the above results on the question of the evolution of free Nitrogen from the
Nitrogenous Constituents of plants during growth.

We have thus far only considered the above results so far as they bear upon the
question of the assimilation of free Nitrogen by plants. But from the constancy of the
amount of combined Nitrogen maintained in relation to that supplied, throughout the
experiments, they afford evidence of an important kind in regard to the converse
question of whether plants give off free Nitrogen during growth. With no less force
than they point to the absence of any assimilation of free Nitrogen, do these results
show that, under the circumstances of growth involved, there has been no evolution
of free Nitrogen from the nitrogenous compounds of the growing plant. At all events,
the assumption that an evolution of free Nitrogen has taken place implies, as in the
case of the experiments discussed at pp. 513, 514, the still more improbable one, that
there has been an exactly compensating amount assimilated. But since the conditions
of the experiments now under consideration were arranged with special reference to the
question of assimilation, they necessarily do not embrace all the circumstances which,
& priort, would be considered the most favourable for the evolution of free Nitrogen
during growth.

Various experimenters, from the time of Dr SavssuRE until quite recently, have enter-
tained the idea of the probability of the decomposition of nitrogenous compounds, and
the concomitant evolution of free Nitrogen, during the growth of plants. We are
ourselves engaged in following up the subject, by methods better qualified to settle the
question than those adopted in regard to the question of assimilation of Nitrogen. We
shall therefore not treat of this subject any further here, than to call attention to the
incidental bearing upon it of the results now under consideration.

The fact that there has been no decomposition of nitrogenous compounds and loss of
Nitrogen as the result of growth, in the particular conditions to which these experimental
plants were subjected, affords little evidence that mo such decomposition could take

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 529

place under any other circumstances. When supplied with an insufficient quantity of
nitrogenous matter, the vegetable organism might not decompose any of that matter;
and yet, when an excess of combined Nitrogen was supplied, the decomposition might
occur. The results we have given, therefore, afford evidence against the fact of such
decomposition only within a very limited range of circumstances of growth. In dis-
cussing the results of the experiments the consideration of which we are now about to
enter upon, we shall refer to this question again, in connexion with circumstances of
growth which we should suppose would be more favourable to an evolution of free
Nitrogen by the plant.

II.—£xperiments in which the plants had a known supply of combined Nitrogen beyond
that contained in the Original seed.

We have thus far considered the subject of the assimilation of free Nitrogen, by
reference to the results of experiments upon plants grown without any supply of com-
bined Nitrogen beyond that contained in the seed sown. We have found that, under
these conditions, we have only been able to study the results of growth of a very limited
character. The wheat, and barley, and oat plants, grown in 1858, did indeed progress
so far as to produce glumes and pales for seed; but they did not afford the opportunity
of studying the results of growth during the period of the formation and the ripening
of seeds themselves.

It yet remains to consider, therefore, what may take place under circumstances of
a more active and vigorous growth, and at a later stage of development of the plant.
When considering the conditions apparently the most favourable for the assimilation of
free Nitrogen by plants (p. 517 et seqg.), we suggested the improbability of such an
assimilation taking place in the presence of an abundant supply of combined Nitrogen.
If the force of our remarks on this point be admitted, and it be still supposed that an
assimilation of free Nitrogen is possible with vigorous growth, only attainable by means
of a liberal supply of combined Nitrogen, we seem to be led to the following paradoxical
conclusions :—

1. Healthy, active, and vigorous growth are favourable conditions for the assimilation
of free Nitrogen by plants.

2. Healthy, active, and vigorous growth can only be attained by keeping within the
reach of the plant an excess of combined Nitrogen.

3. Assimilation of free Nitrogen cannot take place in the presence of an excess of
combined Nitrogen.

A priori conclusions with regard to the effect of molecular forces, and particularly of
those which give rise to vital phenomena, are, however, very unsafe; and we have not
been satisfied to rely upon such evidence only, in reference to the question under investi-
gation, as could be afforded by experimenting with plants grown without an extraneous
supply of combined Nitrogen. We have found that active and vigorous growth cannot
be attained under the conditions provided, when no more combined Nitrogen than that

Aca

530 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

contained in the seed sown is supplied. We have made a series of experiments, in which
such growth was attained by means of a supply of combined Nitrogen beyond that con-
tained in the seed. It remains to see whether, under these conditions of growth, the
assimilation of free Nitrogen can take place, and thus the above paradox be obviated
by the proof that the last of the three suppositions is incorrect.

It is true that we have pointed out the improbability of an assimilation of free Nitro-
een in the presence of an excess of combined Nitrogen only so far as the vital process
of the vegetable cell is concerned. In that intermediate process by which oxygen is
taken up and carbonic acid formed in the cell, the results due to an excess of com-
bined Nitrogen might be different.

‘Thus, the more active the growth, the greater must be the amount of newly-formed
carbon-matter capable of consuming oxygen, when the plant is removed from the
influence of sunlight into the dark. That is to say, the more vigorous the growth in
the sunlight, the greater might be the reducing power of the plant in the dark. The
ereater the reducing power of the plant, the more nearly will the tendency of its mole-
cular forces approximate to an evolution of hydrogen which, in the presence of free
Nitrogen dissolved in the fluids of the cell, may tend to form ammoniacal compounds,
to be, on the retum of light, appropriated by the plant in the exercise of its growing
functions. In connexion with this point, it may be here mentioned that in our investi-
gation of the gases given off by plants under different circumstances, we have had an
evolution of oxygen one day as a coincident of growth, and an evolution of hydrogen
the next as the result of decomposition.

Our experiments in which the plants have been manured with limited amounts of
combined Nitrogen will not only enable us to meet some of the questions above
suggested, but they will also prove whether or not the conditions of soil, atmosphere,
temperature, &c., to which our experimental plants have been subjected were consistent
with active and vigorous growth.

The fact of the evolution of Nitrogen in the decomposition of nitrogenous organic
matter, illustrated in Sub-section D, p. 497 et seg., indicated the danger of using such
matter as a source of supply of Nitrogen. We have therefore used solutions of sul-
phate of ammonia (see Appendix, p. 542), by means of which we haye been enabled to
supply the plants with known quantities of combined Nitrogen at pleasure, as the pro-
gress of growth seemed to require.

In the following Table (XIV.) are given the numerical results of the experiments on
the question of the assimilation of free Nitrogen in which the plants were supplied with
combined Nitrogen beyond that contained in the seed sown. See also figs. 7, 8, 9, 10,
11, and 12, Plate XV., showing the.character and extent of growth of six Graminaceous
plants with extraneous supply of combined Nitrogen, corresponding to the six above
them without such supply.

531

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§32 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

As in the case of the experiments already considered, so again with those to which
the Table just given relates, it is seen, by reference to the last column, that there was a
slight gain of Nitrogen in the experiments of 1857, but, almost without exception, a loss
rather than a gain in those of 1858. Considering that there was a possible source of
gain in 1857 in connexion with the slates used in that year (as explained below), and
with the results of 1858 showing generally a loss rather than a gain when slates were
not employed, we can interpret the whole in but one way.

In order to bring out fully the evidence afforded by these results of experiments in
which the plants were supplied with more or less of combined Nitrogen during the pro-
gress of growth, we must consider them in three separate aspects :—

1. As regards the actual gain or loss of Nitrogen, as indicated by the figures given in
the last column of the Table (XIV.).

2. As presented in the physiological evidence afforded during growth.

3. As exhibited on comparison with the experiments in which the plants had no other
supply of combined Nitrogen than that of the original seed.

1. The Numerical Results of Table XIV.

Much that has been said with respect to the plants grown without extraneous supply
of combined Nitrogen applies with equal force to those now under consideration ; and,
so far as the evidence relating to the latter is of a different character, owing to the
amount of combined Nitrogen at the disposal of the plants, it still is no more indicative
of an assimilation of free Nitrogen than was that obtained with the plants grown with-
out any artificial supply of combined Nitrogen.

In illustration of the probability that the slates used as lute-vessels were a source of
Nitrogen to the plants grown in 1857, some of the observations made during growth
should be adverted to. It is seen that the barley grown in pumice (1857) gives the largest
gain of Nitrogen; and it was observed that, soon after watering with the fluid drawn off
from the surface of the slate, the pumice became covered with a slight coating of green
matter. And nearly all the slates were found at the end of the experiment to have a
slight coating of similar character beneath the pans in which the pots which contained
the plants stood; whilst, in the experiments of 1858, when glazed earthenware lute-
vessels were employed, no such phenomenon was observed.

The slight loss of Nitrogen exhibited in the experiments of 1858 is easily accounted
for on a consideration of the conditions involved. With regard to the peas, clover,
and beans, the physiological circumstances of growth detailed in the Appendix, taken
in connexion with the evidence that has been adduced as to the loss of Nitrogen during
the decomposition of nitrogenous organic matter, must be supposed to explain the loss
in their case, as in some of the experiments in which no extraneous supply of combined
Nitrogen was employed.

The loss of Nitrogen indicated in the cases of the wheat, barley, oats, and buck-

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 533

wheat (1858) would not be so easily explained, had not the Nitrogen in the drain-
water remaining at the end of the experiment been determined. Our object in doing
this was twofold :—

1. To ascertain whether the luting at the bottom of the shade had allowed rain-water
to pass, thus affording a source of combined Nitrogen to the plants.

2. To see if the plants growing in soil to which combined Nitrogen was added, had
evolved any ammonia.

It was, of course, not possible to accomplish both these purposes. But the fact that
ammonia was found in the condensed water only in the cases where there was a Joss in
the total quantity of combined Nitrogen would lead to the inference that both the pre-
sence of ammonia in this water, and the loss of combined Nitrogen in the experiment,
were due to the same cause.

The condensed water showing the amount of combined Nitrogen recorded in the Table
(XIV.) was that which had been evaporated and condensed during the last four weeks of
growth (1858); and during this period the high temperature, and the advanced stage of
the plants, were favourable to the evaporation of ammoniacal water. A considerable part
would condense on the interior of the shade, owing to its comparatively low tempera-
ture; but a certain quantity of that which was in the state of vapour during the passage
of the air through the apparatus would be borne forward into the sulphuric acid in the
bulb-apparatus M, and thus occasion a loss in the amount of combined Nitrogen deter-
mined in connexion with the plants. The reason why the loss is greater with the oats
(as it is in both experiments) than with the other cereals is not perfectly clear; but the
circumstances of growth seemed to afford some explanation of the fact. In one case, at
least, they ripened at a much warmer period of the season, and they became much drier
in stem and leaf, and were therefore more liable to evolve ammonia. On these points,
the circumstances of growth detailed in the Appendix should be consulted.

In considering the column of gain or loss of Nitrogen, it is very desirable to take into
account the total quantity of Nitrogen at the disposal of the plant, in the different series
of experiments. It is also important to consider the amount of growth in the experi-
ments made under the different conditions. The following Tables (XV. and XVI.) bring
out the character of the results in these respects more clearly than they can be gathered
from Tables XII. and XIV. Table XV. shows, for the plants grown without supply of
combined Nitrogen beyond that contained in the seed, and Table XVI. for those grown
with such supply, the dry matter, and the Nitrogen, per seed sown,—the dry matter,
and the Nitrogen, in the total produce of each seed that grew,—and the per cent. of the
total Nitrogen at the disposal of the plant which it appropriated. Finally, the last two
columns of Table XVI. show the amounts of dry matter, and of Nitrogen, in the pro-
duce grown with the extraneous supply of combined Nitrogen, in relation to those in
the produce grown without such supply.

534

MR. J. B. LAWES, DR. GILBERT, AND DR.

PUGH ON

TaBLe XV.

Numbe

r of

General particulars of the Experiments. Heeds. Dry Matter. | Nitrogen.
| Tate Git: . In Pro-! Pp
Year, Description Description of That || Per | Produce, vei Per seed Produce that fn rene
Ko. of Plants. Soil or Matrix. Sown. grew. ba ss erg seed sown. ps reced | seed j8ist
| grew. | taken | ‘het erew-| taken | duce
Graminacezx.
grm. | grm. ] grm. grin.
Wheat ...'/Prepared soil ...... 6 5 0" rO511 02824 | ...... 000133 | 000144 108°3t 051
1857 ...4 Barley .../Prepared soil ...... 6 6 ||0:0449' 01350 | 3°01 | 000093 0-00078 83-9 058
Barley .../Prepared pumice. 6 6 Mier 01542 348 | 000095 0:00075 806 0-48
Meee ...|Prepared soil ...... 8 8 | 0:0504 02175 431 | 000098 000070 71-4 0-32
1858 ...4 Barley .../Prepared soil ...... 8 6 | 0-0403 0-0933 | 231 | 0-00071 000052 732 0-54
Oats ...... Prepared soil ...... 8 8 00357 01435 | 4:02 | 000080 0000525 656 036
Wheat ...'Prepared soil ...... 8 7 ||0-0504 0-15143 3-00 | 000098 0-00058 592 0-38
1858,A.*¢ |Barley ...'Prepared soil ...... 8 8 | 0:0401 0°0888 | |
Oats ...... Prepared soil ...... 8 7 | 00360, 0:09857, 2-74 || 0:00080 |0:00054 67:5 | 055
Leguminose.
1857 ...... Bean ...... Prepared soil ...... 2 2 | 07492) 3514 | 4°69 | 0-03980 | 0-03145 9-0 0°89
| |
1858 ‘Bean ...... Prepared soil ...... 3 3 | 0:4940 16250 | 329 | 0-02500 | o-0245 98-0 151
Say bedi wee Prepared soil ...... 3 3 0: 1802 0°3233 | 1:79 | 9-00630 | 0-0034 | 54-0 1-05
Other Plants. |
l | l
1asBies. ‘Buckwheat Prepared soil ......| 24 | sql /0-03461) ..... | 000083 0-00054 | 65-1 156
TaBLe XVI.
General particulars of the Experiments. Aree ub | Dry Matter. Nitrogen.
eee: | Relation of Pro- |
| j duce per seed |
| | | itn ‘Pro- | with a }
| In Pro- duce, | to that without
= _ 5 | pew In Pro-| duce, 5 o ae Lael that in = | it taken as 1.
. ti ipti That * 4| that 8 duce ec a
met rene Boil or - Matrix. Sown a seed per seed see “a aa Bae ad fal | a Oy
ENE a taken | that grew. manure a a |
crew, 1 taken | ne Dry | Nitro-
as 100. | oS gen. j
Graminacee.

Foal 5 germ. grm.
Wheat .../Prepared soil ...... 3 2 (0-0512 34175. 66°75 0-00133 001205 | 73-2 | 035 12:10 | $36
1857 Wheat .../Prepared pumice | 3 3 | 00514 1:2740 24-79 0-001383 (000710 64:7 | 055 451 4:93
Barley .../Prepared soil ...... 4 3 || 0:0451 1:0113 22-42 | 0-00092 | 0-00513 | 47-2 | 051 749 «658
Barley ....Prepared pumice | 4 4 | 0-:0455 1:1002 24-18 | 000092 0-00362 | 54:1 | 0:33 | 7-13 | 4:83
: |
Wheat .../Prepared soil ...... 4 4 | 00510 1.8975 35°83 ! 000103 | 0-00995 | 728 | 0-54 | 8-40 | 14-21 |
1858 ...4 Barley ...|Prepared soil ...... 4 2 | 0:0399 27350 69:24 0:00070 |0-:01745 | 70-5 | 064 29°31 | 34-21 |
Oates. -: Prepared soil ...... 4 3 | 0-0362 0-4013' 11:08) 000080 0-00416 45-9 | 104 | 2-80 7-92
| |
{| ...|Prepared soil ...... 4 4 | 00515 0-9550! 18:54 0:00100 000452 | 67-5 | 047 | 631 | 7-79
1858,A.*, [Barley ...'Prepared soil ...... 4 3 | 0:0405 0:9933 24:52 0-00072 0-00533 62-2 | 0-54
ats ...++. Prepared soil ...... 4 2 || 00360 0:6400 17-78 || 0-00080 | 0:00730 | 56-1 | 1-14 | 6-49 13:52
Leguminose.
1858 eg ee nares Prepared soil ...... 3 3 | 0:1797| 0:3366) 187 | | 0-00623 0-00380 | 50-2 | 1-13 —
“| !Clover ...|Prepared soil ...... Le peat | Mase | eats Lesson ere ctor es 44-0 /
'
1858, A.* [Bean ......|/Prepared soil ...... 3 | 3 | 0:3646) 1-4333] 3-93 || 0-01743 | 0-01337 | 56-4 | 0-93 |
Other Plants.
1858 ...... ‘Buckwheat| Prepared soil ....-. | 42 | 24 | 0-0202 0-0 21) 4-06 | 0-00047 | 0° 0-92 | 2:37 | 141 |

* These experiments were conducted in the apparatus of M. G. Vite.
+ There is here evidence that a part of the Nitrogen of the seed that did not grow was appropriated by the plants growing from

the other seeds.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 535

There are several obvious inferences to be drawn from the figures in these Tables.
To some we shall refer further on, in the proper order of the discussion. We here
simply call attention to the very great increase of growth when an extraneous supply of
combined Nitrogen was provided, as exhibited in the last two columns of Table XVI.

2. Consideration of the Physiological Evidence as bearing upon the question of
the assimilation of free Nitrogen.

However directly the quantitative details given in the Tables may bear upon the
question at issue, it is very important to consider them in connexion with the physio-
logical details of the experiments. In order to estimate the value of the evidence
afforded in this particular, the indications manifested from the earliest period of growth
should be noticed.

Reference to the Notes of the progress of the plants, given in the Appendix, will
show that all the plants when they first came up looked green and vigorous, indicative
of their being at that period in circumstances embracing all the conditions essential to
healthy growth. As already pointed out, they at that time were probably supplied
with an excess of combined Nitrogen in relation to their immediate wants. After some
days, varying with the nature of the plants, they began to lose their deep-green colour,
and to assume a lighter-green, or pale-yellow tint, indicative of a want of combined
Nitrogen. We have already pointed out how favourable, probably, would be the con-
ditions here afforded for the assimilation of free Nitrogen, when the plant was passing
from the state in which it had an excess to that in which it had a deficiency of com-
bined Nitrogen for the demands of growth. The vigorous development of the plants
grown in garden soil, but under the same conditions as to atmosphere, &c. as the other
experimental plants, indicates that the conditions of atmosphere provided in the experi-
ments were not at fault (see Appendix, Experiments Nos. 12, 1857, and 15, 1858; also
fig. 13, Plate XV.). In order to test whether the sum of all the conditions, excepting
those connected with a sufficient supply of combined Nitrogen, were appropriate for
vigorous growth, we have only to provide some combined Nitrogen when the plants
show the declining vigour just described; and if this be all they require, they will
resume their healthy green colour. Or if we add the combined Nitrogen before the
plants arrive at the period in question, it will prevent them assuming the pale-green
or yellow colour. We have had recourse to both of these expedients; and each, so far
as the Cereals, buckwheat, and clover are concerned, has yielded a result indicating that
all the conditions of the experiments, excepting those connected with a sufficient supply
of combined Nitrogen, were adapted for healthy growth.

The plants to which ammonia was given in 1857, were allowed to suffer more before
they received it than those of 1858; yet in thirty-six hours after the addition of com-
bined Nitrogen to the soil, in amount not exceeding 1} milligramme of the element to
each plant, they began to manifest an improved appearance. In two or three days the
improvement was quite marked; but at the termination of periods varying from nine to

MDCCCLXI. 4D

536 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

eighteen days, the plants seemed to have consumed all the combined Nitrogen supplied
to them—or rather all of it that had not become inaccessible to them in the soil.
They then began to manifest the same indications of defective supply as before. Plants
so. circumstanced must therefore, at a more advanced stage of growth than before they
had been supplied with ammonia, have passed from a point at which they had an excess
of combined Nitrogen, to that in which they had an insufficiency. They must hence,
again, have been subjected to those conditions which we have assumed to be probably
very fayourable to the assimilation of free Nitrogen.

Reference to the details of growth given in the Appendix will show that several
times during the progress of the plants the above phenomena were manifested. A new
increment of combined Nitrogen caused a new increment of growth, a greener colour,
and a more vigorous appearance generally. This was soon followed by the recurrence
of the pale colour. In some instances, more ammonia was not supplied until the plants
seemed almost past recovery: in a few cases they were quite so. The addition of
ammonia now (excepting in the few cases just referred to) produced a revivification, to
be followed in a short time by the indications of some want, and so on.

A considerable range of conditions of growth was thus provided. Just after each
addition of combined Nitrogen the plants must have been supplied with an excess of
this element in an available form. ‘The evidence of this was afforded in the obviously
increased means of consumption, evinced in the formation of new shoots from the base
of the plants, or from their nodes. But these new shoots were too vigorous to allow the
plants to go on long without suffering for want of a new supply of combined Nitrogen.
In passing to this point, the newly-formed and yigorously-growing portion of the
vegetable matter would be in the condition we haye assumed to be the most favourable
for assimilating free Nitrogen. Instead of doing this, however, it soon began to suffer,
and continued to do so until a new supply of combined Nitrogen was added, when new
vigour succeeded, to be followed again shortly by a cessation of growth. This cycle
of conditions, repeated several times during the growth of the same plant, and the
experiment similarly conducted with a number of pots of plants of different kinds, with
like results in all the cases, affords a wide range of circumstances such as we have
assumed to be favourable to the assimilation of free Nitrogen; but such an assimilation
has not taken place.

Without the physiological details, it might not have been clear that the plant had
not an excess of combined Nitrogen at its disposal during the greater period of its
growth after the addition of the artificial supplies of it, since a considerable proportion
of that added remained in the soil at the termination of the experiments, as Tables XTV.
and XVI. show. But it is not difficult to imagine that a few milligrammes of ammonia
intermingled with 1500 or 1600 grammes of soil (and pot), might become distributed
over such an extent of surface, and be so completely absorbed, as that a considerable
proportion should remain inaccessible to the plant. The physiological evidence leaves no
doubt this was the case.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 537

The Graminaceous plants of the experiments of 1858 were supplied with a consider-
able quantity of combined Nitrogen at an earlier period of growth than those of 1857
(see Tables showing the dates of addition, Appendix, pp. 542, 543), and they were not
allowed to exhibit such marked signs of decline of vigour before receiving their fresh
supplies. There is, however, no marked distinction in the proportion of the total supply
appropriated by the plants, and left in the soil, respectively, in the two cases.

The Graminacee under the title of ‘©1858, A” (those grown in M. G. VILLE’s case)
were treated similarly to the others of 1858, excepting that the combined Nitrogen was
given to them at an earlier period of their growth, and they were not allowed to suffer
at any time for want of it. We shall notice the difference in result presently.

In addition to the evidence of the physiological phenomena as bearing upon the
amount of growth due to the supply of ammonia, attention should be called to the
remarkable character of growth which was manifested. ‘The evidence afforded on this
head, is of interest in considering the question of the character of the conditions most
favourable to the assimilation of free Nitrogen; and it also brings to view some remark-
able features in vegetable physiology.

It will be seen, by reference to the Notes in the Appendix, that, shortly after the
addition of ammonia for the first time to the Graminacez (1857 and 1858), the plants
began to throw out new shoots at the base of the principal stem. It would thus appear
that the plant, being supplied at the commencement of its growth with only the limited
quantity of combined Nitrogen contained in its seed, had developed a stem commensu-
rate with that quantity. But when new quantities of combined Nitrogen were placed
at the disposal of the plant, forces were thus called into activity which were greater
than could operate through the medium of the original stem. Some of the new shoots
have come forth close to the surface of the soil, some at the first, and some at the second
nodes. ‘The character of growth in this respect can be best studied by reference to the
drawings of the plants given in Plate XV.

Another and no less remarkable feature was the formation of roots at the second and
third nodes above the ground in the case of most of the Graminaceous plants to which
ammonia-salt was added as manure (see Plate XV.). These roots came out around the
node, and extended downwards—seyeral of them reaching the soil from heights varying
from } to 13, or even 2 inches, and penetrating it to the bottom of the pot. The most
marked instance of this kind of growth was that of the barley represented in fig. 11,
Plate XV., and in more detail, with special reference to the points now under con-
sideration, in fig. 16, Plate XV. As will be seen in the figures, roots and new stems
come from the same node, making the latter a veritable starting-point, or new axis
of growth, like the seed in the first instance. The original stems, below these nodes,
did not increase much in size beyond what they had attained before the addition of
ammonia; but the stems above the nodes became much larger than the portions below
them, as also did those of the new shoots.

Finally, so long as the conditions of growth of the plants were such that an addi-

4p2

538 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

tional supply of combined Nitrogen would cause increased development, so long must
the physiological conditions have been such as to require available Nitrogen, and they
must therefore have been more or less favourable to the assimilation of free Nitrogen,
provided such assimilation were possible. Hence, the fact that this did not take place
under the circumstances which have been described, seems to show that, at least in the
case of these Graminacez, it is not possible.

Some of the remarks which we have made with regard to the influence of a supply of
combined Nitrogen upon the growth of the Graminacew, apply also, in a greater or
less degree, to the other plants experimented upon. We shall not comment here in
detail upon the value of each experiment, but simply call attention to the columns of
gain or loss of Nitrogen, in the Tables, and to the notes in the Appendix indicating the
circumstances of growth of the plants.

With regard to the Leguminose experimented upon, it is to be observed that the
development was by no means so satisfactory as in the case of the Graminacee. Hence
the evidence which the results relating to them afford against the fact of assimilation
of free Nitrogen must be admitted to apply to a more limited range of conditions of
growth, and, therefore, to be less conclusive against the possibility of such assimila-
tion. Still, so far as they go, the results with these plants, and also those with buck-
wheat, tend to confirm those obtained under the more favourable circumstances of
growth with the cereals. It will be remembered, however, that M. BoussinGAavLt expe-
rimented with a great many Leguminous plants, and generally succeeded in getting
much more healthy growth than we were able to do in the cases to which the figures in
the Tables refer. Yet in no case did he find any such gain of Nitrogen as to lead him
to the conclusion that these plants, any more than the Graminacee, assimilated free or
uncombined Nitrogen. Our own experiments with Leguminous plants are, however,
not yet concluded; so that we hope to supply some additional evidence on this subject,
on a future occasion.

Relations of the Plants grown with a supply of ammonia to those grown without it.

We have already called attention to the fact that the physiological phenomena exhi-
bited in the progress of the plants grown under the two different conditions as regards
the supply of combined Nitrogen at their disposal, afford satisfactory evidence that the
conditions provided in soil and atmosphere were all that were requisite in experiments
for the solution of the question at issue with regard to the Cereals. ‘The great develop-
ment of these plants when ammonia was supplied (which was in fact almost in pro-
portion to the amount supplied), the cessation of growth with the limit of the supply,
together with the contrast between the growth with the aid of the ammonia and that
without it, all afford evidence in one direction in regard to the question at issue, so far
as these plants are concerned.

In Table XIV., relating to the plants to which ammonia was supplied, an experiment
with clover is recorded. Reference to the remarks in the Appendix, p. 573, will show

-

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 539

that we failed to get any growth with clover without the addition of ammonia.
Hence, excepting so far as this fact is itself a point for remark, no contrast can be
drawn between the growth of this plant with and without an extraneous supply of
combined Nitrogen.

From what has already been said, it will be easily understood that the contrast be-
tween the beans and peas grown with and without the addition of ammonia is not
very satisfactory. These plants proved to be so sensitive, under the conditions provided
in the experiments, that it was obvious that, in many cases, they suffered from other
causes than a want of combined Nitrogen, which we were not able to control. In but
one experiment with such plants, that with the bean “1858, A.” (Table XIV.), was the
influence of a supply of combined Nitrogen so marked as to indicate that the plants
were previously suffering for want of such supply. It will be seen, by reference to the
Table, that, in the case here referred to, the seeds sown contained 0:0523 gramme of
Nitrogen, and that 0:0188 gramme was added in the form of ammonia-salt—making in
all 0-0711 gramme of combined Nitrogen involved in the experiment. Of this the
plants appropriated 0:0401 gramme—about one-fifth less, therefore, than was supplied
in the seeds alone. Yet, although the numerical results, taken by themselves, thus
afford but little evidence of the effect of the 0°0188 gramme of Nitrogen added in
the form of ammonia, the increased vigour of growth on the addition did afford such
evidence. In contrast with this single result, however, attention may be called to the
results with the beans grown without any other supply of combined Nitrogen than that
contained in the seed sown. The bean plants so grown in 1857, appropriated nearly
four-fifths of the Nitrogen of their seed; and those grown in a similar way in 1858,
appropriated a considerably larger proportion of the combined Nitrogen so provided
to them.

From a review of the whole of the results considered in this Section, it appears, then,
that in the case of the Graminaceous plants experimented upon the growth was the
most healthy, and such as provided a wide range of conditions for the assimilation of
free Nitrogen, provided this were at all possible. The growth of the Leguminous plants
was not so healthy, and did not, therefore, provide such a wide range of conditions for
the possible assimilation of free Nitrogen. Nor was the growth of other plants so satis-
factory as that of the Graminaceous ones. In all, the growth was more or less increased
by the supply of combined Nitrogen beyond that contained in the seed. The effect of
such supply was the most marked with the Graminaceous plants—the increase in the
produce of dry vegetable substance due to extraneous supply of combined Nitrogen
being, in their case, eight, twelve, and even nearly thirty-fold, according to the amount
of Nitrogen so provided. Yet, with nineteen experiments with Graminaceous plants,
six with Leguminous ones, and some with plants of other descriptions—with such great
variation in the amount and character of growth in the several cases—and with such
great variation in the amount of combined Nitrogen involved in the experiments, in

540 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

no case have the results been such as to lead to the conclusion that there was an assi-
milation of free, or uncombined, Nitrogen.

The results of the whole inquiry may be very briefly enumerated as follow :—

The yield of Nitrogen in the vegetation over a given area of land, within a given time,
especially in the case of Leguminous crops, is not satisfactorily explained by reference
to the hitherto quantitatively determined periodical supplies of combined Nitrogen.

Numerous experiments have been made by M. Boussineavt, from which he concludes
that free or uncombined Nitrogen is not a direct source of the Nitrogen of vegetation.
M. G. ViL18, on the other hand, concludes, from his results, that free Nitrogen may be
a source of a considerable proportion of the Nitrogen of growing plants. The views, or
explanations, of other experimenters, on this disputed point, are various, and incon-
clusive.

It was found that the conditions of growth adopted in our own experiments, on the
question of the assimilation of free Nitrogen by plants, were consistent with the healthy
development of various Graminaceous plants, but not so much so for that of the Legu-
minous plants experimented upon.

From the results of various investigations, as well as from other considerations, we
think it may be concluded that, under the circumstances of our experiments on the
question of the assimilation of free Nitrogen by plants, there would not be any supply
to them of an unaccounted quantity of combined Nitrogen, due either to the formation
of oxygen-compounds of it under the influence of ozone, or to that of ammonia under
the influence of nascent hydrogen.

We have found that free Nitrogen is given off in the decomposition of nitrogenous
organic matter, under certain circumstances. But, considering the circumstances of
such evolution, and those to which the nitrogenous organic matter necessarily involved
in experiments on the question of the assimilation of free Nitrogen by plants is sub-
jected, it may, we think, be concluded that there would be no loss of combined Nitrogen
from this cause in such an experiment, excepting in certain cases, when it might be pre-
supposed.

Our experimental evidence, so far as it goes, does not favour the supposition that
there would be any loss of combined Nitrogen in our experiments on the question of
assimilation, due to the evolution of free Nitrogen from the nitrogenous constituents of
the plants during growth.

In numerous experiments with Graminaceous plants, grown both with{and without
a supply of combined Nitrogen beyond that contained in the seed sown, in which there
was great variation in the amount of combined nitrogen involved, and a wide range in
the conditions, character, and amount of growth, we have in no case found any evidence
of an assimilation of free or uncombined Nitrogen.

In our experiments with Leguminous plants the growth was less satisfactory; and

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 541

the range of conditions possibly favourable for the assimilation of free Nitrogen was,
therefore, more limited. But the results recorded with these plants, so far as they go,
do not indicate any assimilation of free Nitrogen. Since, however, in practice, Legu-
minous crops assimilate, from some source, so very much more Nitrogen than Grami-
naceous ones, under ostensibly equal circumstances of supply of combined Nitrogen, it
is desirable that the evidence of further experiments with these plants, under conditions
of more healthy growth, should be obtained.

Results obtained with some other plants are in the same sense as those obtained with
Graminacee and Leguminose, in regard to the question of the assimilation of free
Nitrogen.

In view of the evidence afforded of the non-assimilation of free Nitrogen by plants
under the wide range of circumstances provided in the experiments, it is desirable that
the several actual or possible sources of combined Nitrogen to plants should be more
fully investigated, both qualitatively and quantitatively.

If it be established that the processes of vegetation do not bring free Nitrogen into
combination, it still remains not very obvious to what actions a large proportion of the
existing combined Nitrogen may be attributed.

542 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

APPENDIX.
Received subsequently to the reading of the paper.

A.—Preparation of solutions for manuring the Plants, dates of application,
and quantities applied.

Sulphate-of-Ammonia solution.—Ordinary ammonia-water was distilled from a flask,
the vapour condensed in a receiver containing pure distilled water, and the strength of
the solution determined by the volumetric method, by means of dilute sulphuric acid of
known strength, the preparation of which is described further on, at p. 545. <A given
volume of the ammoniacal liquid thus prepared was neutralized by pure dilute sulphuric
acid, of which the quantity added was determined by measurement, and the strength of
the solution calculated accordingly. It was intended that each cubic centimetre should
supply about one-tenth of a milligramme of combined nitrogen. The exact strength of
the sulphate-of-ammonia solutions used in the course of the experiments was as under :—

TABLE I.

Combined nitrogen in a
pipette measure of the

Volume of the pipette

measure employed. aGlndaaa

septems*. gramme.
In the experiments of 1857 ......... sonntotes 111-2 0-00578
In the experiments of 1858, to “August 10 inclusive. sgnecoces 100-0 0-004
In the experiments of 1858, after August 10. =O COSCO CE 100-0 000359

Tables II. and III. show the dates of the application of the above solutions to the
different plants, and the amounts of nitrogen so supplied.

TaBLE II].—Showing the supply of combined Nitrogen, as Sulphate-of-Ammonia solution,
to plants grown in 1857.

Nitrogen supplied.
Dates.

Wheat, in pre- | Wheat, in pre- | Barley, in pre- | Barley, in pre-
pared soil. pared pumice. pared soil. pared pumice.
gramme, gramme. gramme.
June 0'.:.. -. “00578 “00578 *00578
Un aaa *00578 *00578 *00578
July WW <...:: “00578 “00578 *00578
July 22 ...... *00578 *00578 “00578
2 JULY MeO cones. *00578 “00578 0057
Total 2c: 02890 “02890 02890

* A septem measure is that of 7 grains (=xe5s of a pound avoirdupois) of water; that is, rather less
than half a cubic centimetre, which is equal to 15-43235 grains (or 1 gramme) of water.

>

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 543

TasixE I1I.—Showing the supply of combined Nitrogen, as Sulphate-of-Ammonia
solution, to plants grown in 1858.

Nitrogen supplied.

Dates. |
Wheat. Barley. | Oats. |Wheat*.|Barley*.| Oats*. | Pea. | Clover. | Bean *.
grm. | grm. | grm. | grm. | grm. | grm. | grm. | grm. | grm.
May 22 ...............|°0040 |-0040 | :0040
JUNE) dienaesnesseesees| 004 0Nic0040N (0040) pee eeen |eceeee| eee 0040 | -0040
Junec2lr Siu. weseesecc 0040 | -0040 | -0040
JUNE ZO wceeevensasices CUDA CUTER) WRU essced | icaooas | cooosts | uocoone -0040
JUVewSrccesccetscens: SCOZOM OOF MN OOLO) eer accall veces si ilu csersenialluomeies 0040
itthygeU2Poewecelescteceess|(50 040) "00408 [tO 040! (rece. ce Il sects. sll teseneen hommes 0040
July 14 ...............] 0040 | 0040 | -0040 |-0040 |-0040 |-0040 | .. ... 0040 | :0040
July 19 ...............|°0040 |-0040 | ...... 0040 |:0040 |:0040 | ....., 0040 | -0040
JULY) SSE ssccesneeeesece|eoseee 0040) | \.<2... 0040 | 0040 | -0040 | ...... 0040
Duly (29s. hese eccst ene 0040
Aue use WOM s.scscse=<|(20040) |) secce. Cuotoo.|||! cadecs |] concn: |I\\con000" |! “ecoho 0040
August 17 ............|°0036 |-0036 | ...... 0036 | 0036 |-0036 | ...... 0036 | 0036
/ NUP EE eoaasseccecd| eebees 0036
August) 2Oleeedsceee 0036
September 7 ......... 0036 |-0036 | ...... 0036 | -0036 |-0036 | ...... 0036 | +0036 | °0036
SYCLOBER TO An ce <ehe aval p ccctoarv' ln nice | eesecet | aecceea mmeceal lh coat etis 0036 0036
Octoberye seer iascscelheccecs, | weedeowm liteecees 0036 |:0036 |-0036 | ...... | ..... “0036 | :0036
Total ............] 0508 | +0468 | +0280 | -0228 |-0228 |-0228 |-0040 |-0428 |-0188 | -0108

Phosphate-of-Soda solution.—The strength of a dilute solution of phosphoric acid was
determined by means of a titrated alkali-solution (for the preparation of which see
page 545); and it was then neutralized by carbonate of soda. Each pipette measure of
this solution given to the plants supplied about -01 gramme phosphate of soda. It was
only employed in the experiments of 1858. In the records of growth of the plants, it is
stated whenever they were manured with this solution.

Sulphuric-Acid solution—The strength of some very dilute pure sulphuric acid was
determined in the same manner as was that of the phosphoric acid, as stated above. It
was then so far reduced, that the pipette measure by which it was applied to the plants
contained exactly as much SO, as the pipette of sulphate-of-ammonia solution then in
use, namely, ‘0114 gramme SO,, corresponding to ‘004 gramme N. For the application
of this solution see the records of growth of the plants.

The value of each of the above solutions was determined by analysis, to ensure that it
was such as was supposed.

B.—Taking up the Plants, preparation for analysis, methods of analysis, &e.

At the termination of growth the glass shade was washed outside, quicksilver was
poured into the groove to displace from it the condensed water not removable by the
arrangement of apparatus of 1857, or already collected in the drain-water bottle
adopted in that of 1858, as the case might be, and the shade was then removed. ‘The

* These plants were grown in M, G, Virx1’s case.
MDCCCLXI. 45

544 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

previously covered portions of the slate or stone-ware lute were then washed with pure
distilled water, and the wash-water was added to the condensed or drain-water. In the
experiments of 1858 this fluid was analysed separately, but in those of 1857 it was
mixed and dried down with the soil.

The pot, with the soil and plants, was removed to a clean table covered with white
paper, the plants measured in all their parts and then cut off at the surface of the soil;
the roots were removed, slightly washed from soil, and observed. ‘The plants were then
put into a small wide-mouthed bottle, generally stem and root together, but sometimes
they were put into separate bottles. In the experiments of 1857 the contents of the
bottles were dried in a water-bath, with a current of air, previously washed through
sulphuric acid, passing through the bottle and thence through a solution of a known
quantity of pure oxalic acid. But it was found that no appreciable amount of ammonia
was thus accumulated. Hence, in 1858, a little oxalic acid (in solution) was added to
the vegetable matter, and the whole dried in the water-bath without the above pre-
caution.

When dry, the vegetable matter was cut small by means of a pair of clean long
scissors, reaching to the bottom of the bottle. In this way the substance was reduced
to a considerable degree of fineness, and it was still further ground up in the mortar
when mixed with soda-lime for analysis. When duplicate analyses were to be made, the
matter was carefully divided so as to ensure equal proportions of stem, fine leafy matter,
&c., in each half. Hence, if both analyses were successfully conducted, the results were
mutually confirmatory; or if one portion were lost, the other still represented a propor-
tionate amount of the whole material.

The soil was removed from the pot to a porcelain dish, and a sufficient amount of a
solution of oxalic acid added to keep it acid. The mixture was then heated on a sand-
bath (stirring constantly) until most of the water was expelled, more fully dried in a
water-bath, and then preserved in well-corked bottles for analysis. The pots were pounded
up; those of 1857 being preserved and analysed separately, and those of 1858 mixed
with the soil before it was dried with oxalic acid. The pieces of flint at the bottom of
the pot were also pounded and mixed with the soil.

For analysis, 150 to 200 grammes of the soil, pot, or mixture, were mixed with about
half the yolume of soda-lime, the whole put into a large combustion-tube, some soda-
lime put in advance of the mixture, and then asbestos, as usual. The combustions
were made in charcoal furnaces, and the ammonia collected in titrated sulphuric acid,
of which the strength, and the amounts employed, are described at pp. 545,546. When
very small quantities of nitrogen were involved, the ammonia from two or three tubes of
substance was sometimes collected in the same quantity of acid, so as to diminish the
error of titration. It was found, however, to be better to use very small quantities of
acid, and to estimate the product of each combustion separately; for, by the former
method, if any accident occurred in the second or third combustion, it involved the loss
of the determination of the products previously collected.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 545

Preparation of the titrated solutions.

A weighed quantity of pure, dry carbonate of soda was dissolved in water, and to the
solution water added to a given volume. As a preliminary step, the strength of some
dilute sulphuric acid was tested against a given volume of the carbonate-of-soda solution;
and from the data thus obtained, by further dilution a large quantity of acid was made
of about the strength desired. The exact value of this acid was then ascertained by
repeated trials with the standard carbonate-of-soda solution. ‘To accomplish this, a
given volume of the soda-solution was put into a beaker, a little litmus added,
and the mixture heated over a spirit-lamp. ‘The acid to be tested was then allowed
to flow from a burette until a wine-red colour (indicating that the carbonate is converted
into sulphate and bicarbonate with carbonic acid in solution) was produced. On boil-
ing, the blue colour is restored ; acid is added until red ; the boiling is repeated, till the
blue returns; acid again added, and so on, until the solution remains red on the addi-
tion of the last drop. The point at which the permanent change takes place in the
first trial being known, the experiment is easily repeated so as to ensure great accuracy.

Thus, 50 septems of a solution of carbonate of soda, of which 1000 septems contained
6652 grammes of the salt, required, for neutralization as above, the following number
of septems of the dilute acid, in six different trials—

58-3, 58:2, 58:3, 58°3, 58:2, 58:2; mean 58-25.
Hence—

6°652 50 N 6°652 50 14

1000 * 58-25 X NaO, CO,= 1000 * 58-25 * 52-98 0001508 gramme N.

The mean of six experiments with a solution of carbonate of soda of another strength
gave in the same way 0:0015008 gramme N; and we adopted the mean, or 0:001504
gramme, as the amount corresponding to one septem of the titrated acid.

It remained to prepare an alkaline solution to test against this standard acid. At first
a solution of sugar-lime was employed; but this being found to be liable to constant
change, due doubtless to fermentation, a solution of caustic soda was had recourse to.
This solution was prepared of such dilution that the extreme error possible in reading
off a unit of volume on the burette should be much less than would be admissible as
the maximum error of analysis. The burette was of small enough diameter to allow of
one-tenth of a septem being read off on it; and the alkali-solution was so dilute that it
required about three septems of it to neutralize one septem of the titrated acid. Hence
one septem of the alkali-solution corresponded to only about one-half of a milligramme
of nitrogen, and the probable error of reading would therefore amount to only about
one-twentieth of a milligramme.

In the case of the sugar-lime solution, it was found necessary to test its strength
against that of the acid every day that it was employed. But the soda-solution, if pro-
perly prepared, and well preserved, remained for months unchanged; so that, when its
value was once established against that of the standard acid, it could be expressed

4E2

546 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

by a number of four or five digits, which, multiplied by the number of septems
of alkali representing the product in an analysis, gave the actual quantity, in grammes,
of the nitrogen to be estimated.

Amount, and measurement, of the titrated acid used in Nitrogen determinations.

It was desirable that at least three times as much acid should be used as would be
neutralized by the ammonia formed. ‘The acid being more concentrated than the
alkali, it required a more exact method of measurement than was afforded by the burette
used for the latter. Pipettes, of which the diameter at the point of reading off is com-
paratively small, and which hence admit of a higher degree of accuracy, were therefore
employed. In the construction of those to be used, care was taken to maintain the same
relation of the diameter of the neck at the point of reading to the entire volume in
instruments of different sizes—a condition seldom observed by makers of pipettes.
When the quantity of nitrogen involved in an analysis was very small—as in the case of
the soils and pots in the experiments without nitrogenous manure—only about six sep-
tems of the titrated acid, measured in a small pipette with a very narrow neck, were used.
The exact volume of the pipette-ful of acid was not a matter of any consequence. It
was only essential to ascertain its exact value expressed in septems of the titrated alkali-
solution. When the amount of nitrogen involved was larger, and more under control—
as for example when grains were to be analysed—care was taken to operate on such a
quantity of nitrogenous material that the number of septems of the alkali representing

its nitrogen should be sufficiently large to render the constant errors of titrating, read-

>?
ing, &c., inappreciable. This end was attained when the substance experimented upon

contained 5 to 8 milligrammes, or more, of nitrogen.

Combustion-tubes, bulbs, &c.

The combustion-tubes used in the determinations of nitrogen in the soils, pots, &c.,
were about 3 feet long and about 1 inch in diameter. The bulb-apparatus was capable
of holding two-and-a-half to three times as much fluid as that usually employed; but the
central and lowest bulb, and particularly its tubular connexions with the other bulbs,
were very small, so that a small quantity of liquid could close the passage. This arrange-
ment was necessary owing to the small quantity of acid frequently used, and the large
amount of water driven off in the combustion from the large quantities of soil and soda-
lime. For the combustion of the experimentally grown plants smaller tubes were
employed; and for seeds, &c., ordinary combustion-tubing was used.

The Soda-lime.

Before use, the soda-lime was ignited with 2 per cent. of pure sugar, in order to
ensure its freedom from ammonia-yielding matter. It was then slaked with pure
distilled water, dried, and kept in well-corked bottles.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 547

Accuracy of the method for the determination of nitrogen by combustion
with soda-lime, &e.

In order to ascertain the accuracy of the method before relying upon it for the pur-
poses of the investigation, a few preliminary experiments were made upon the determi-
nation of small and known quantities of nitrogen, mixed with large quantities of soil,
which had been previously freed from combined nitrogen as in the preparation of the
soils for the plant-experiments. The nitrogenous substance taken for the purpose was

the powdered crystals of purified quadroxalate of ammonia, on ‘ho, (C, O3),+7 HO.

The results were as follow— ‘

Experiment 1.—50 grammes of the prepared soil were mixed with quadroxalate con-
taining by calculation 0:0024 gramme nitrogen; and on burning with soda-lime, and
determining as above described, 0:0027 gramme nitrogen was found.

Experiment 2.—100 grammes of the soil mixed with quadroxalate equal, by calcula-
tion, to 00035 gramme nitrogen, gaye on combustion 0:0037 gramme nitrogen.

The error of analysis was, therefore, three-tenths of a milligramme of nitrogen with the
50 grammes, and two-tenths with the 100 grammes of soil. These results were obtained
at the commencement of the inquiry, with comparatively large quantities of titrated acid,
and therefore before experience had suggested the precautions to be adopted to reduce
the errors of determination to the minimum. They may hence be taken as examples of
the maximum errors of analysis, but they are less than would affect the bearing of the
results in the investigation on the question of assimilation.

Testing for Nitric acid.

The indigo test, as recently refined by BoussincauLt*, and the protosulphate-of-iron
test, were both employed. When nitric acid was sought for and not found, if practicable
the negative result was always confirmed by the addition to some of the substance under
examination of a quantity of nitric acid (in the form of nitrate) less than could affect
any conclusions to be drawn from the fact of its presence or absence in the substance in
question. In all the cases of such addition the re-examination showed the presence of
nitric acid.

The method of BoussINGAULT was much more delicate than the protosulphate-of-iron
test; but, on the other hand, the latter was much less liable to give deceptive indica-
tions, dependent on other circumstances than the presence of nitric acid. In using the
protosulphate test, the aqueous extract of the substance under examination was evapo-
rated to a small volume with excess of fixed alkali, then transferred to a test-tube, and
further evaporated till only a few drops remained. A considerable excess of concentrated
sulphuric acid was then added, and on the surface of the liquid a concentrated solution
of protosulphate of iron was carefully poured without agitation, by means of a small
pipette with a mouth of almost capillary fineness. The characteristic brown tinge
indicated the presence of nitric acid.

* Ann. de Chim, et de Phys., vol. xlviii. (1856) p. 153 e¢ seg.

548 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

C.— ABSTRACT of THE Recorps oF GRowTH OF THE PLANTS.
I.—PLANTS GROWN IN 1857 *.

The following list indicates the original arrangement of the experiments in 1857;
but, as the records will show, beans sown and resown under shades Nos. 5, 10, and 11
died before they had attained any material amount of growth; and hence the products
in these cases were not submitted to analysis.

Series 1. With no other combined nitrogen than that contained in the seed :—

1. Wheat; in prepared soil.
2. Barley; in prepared soil.
3. Barley; in prepared pumice.
4. Beans; in prepared soil.
5. Beans; in prepared pumice.

Series 2. With a supply of known quantities of combined nitrogen beyond that con-

tained in the seed :—
6. Wheat; in prepared soil.
7. Wheat; in prepared pumice.
8. Barley; in prepared soil.
9. Barley; in prepared pumice.
10. Beans; in prepared soil.
11. Beans; in prepared pumice.

And also—
12. Wheat, Barley, and Beans, together; in rich garden soil.

ReEcoRDS OF SOWING, AND EarLy STAGES OF GROWTH, OF ALL THE PLANTS COLLECTIVELY.

May 12.—The weighed seeds of wheat (Nos. 1, 6, & 7), of barley (Nos. 2, 3, 8, & 9),
and of beans (Nos. 4, 5, 10, & 11) were respectively put into small bottles, a few
septems of pure distilled water added to soak them, and then corked up.

May 16.—The wheats (Nos. 1, 6, & 7), and the beans (Nos. 4, 5, 10, & 11), were
sown, and the pots removed to their places on the stand, and covered with the shades ;
seeds all swelled; some sprouting.

May 20.—The barleys (Nos. 2, 3, 8, & 9), freshly weighed seeds (the soaked ones
being abandoned), were set, and the pots removed to their position under the shades.

May 27.—Nearly all show shoots above the surface, all of which look green and
healthy.

June 2.—Wheat and barley plants two or three leaves each, healthy, but pale green.
No. 4 beans (soil) healthy and vigorous. No. 5 beans (pumice) one plant up, with
three leaves speckled with black spots; the other plant blackened and apparently dead.
Beans No. 10 (soil) and No. 11 (pumice) slightly speckled with black spots.

June 3.—Commenced the daily passage of washed air over the plants, in quantity

* The figures (Plate XV.) of the plants grown in 1857 are reduced from drawings taken, for the most
part, about the middle of August.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 549

equal to about 24 times the volume of the shade. Carbonic acid also daily supplied, in
amount as described at pp. 480, 481.

June 6.—Graminaceous plants (Nos. 1, 2, 3, 6, 7, 8, & 9) all healthy, though with a
tendency to turn yellow at the tips of the leaves. Of the Leguminous plants, Nos. 5,
10, and 11 give indications of dying.

June 8.—Some of the wheat and barley plants turning yellow. Beans Nos. 5, 10,
and 11 obviously dying; probably injured by the causticity of the ash added to the soil,
as No. 4 beans, the seeds and roots of which happen to be washed when water is sup-
plied, are healthy and vigorous.

RECORDS FOR EACH EXPERIMENT GIVEN SEPARATELY.

No. 1.—Wheat (1857); six seeds; prepared soil; without nitrogenous manure.
(See Plate XV. fig. 1.)

June 9.—Five plants up; one quite small, the others 2 to 4 inches high, with two
leaves developed and a third appearing; yellowish at the tips of some of the leaves.

June 15.—Five healthy plants, each with three fully developed leaves; tips of the
lower leaves slightly yellow.

June 24.—Plants 5 inches high; lower leaves dead and dry, upper pale green; with
some of the tips yellow, but general appearance of the upper leaves healthy.

July 4.—Plants 6 to 7 inches high; 5 leaves on each; upper ones pale green, lower
ones yellow.

[Note.—Drops of water condense rapidly on the tips of the leaves of all the Cereals,
but not of the Leguminous plants; they also form and run down the inner surface of all
the shades, casting focal rays apparently injurious to the plants when not shaded from
direct sunlight. |

July 11.—Same number of leayes; very little further growth; lower leaves more
dried up.

July 22.—Very little improvement.

July 29.—Very little growth, though upper leaves continue green; but little ten-
dency to form stem.

| Note.—Shade opened a few seconds to substitute a tube for one accidentally broken. |

August 10.—Green colour maintained, but no apparent increase in size.

August 24.—Five plants, 6 to 9 inches high, with eight or nine leaves each, all dried
up but the two upper ones, which are green and healthy, one expanded, the other folded
in the axis of growth. The healthy appearance of the upper leaves has been maintained
several weeks, with otherwise almost total cessation of growth.

October 3.—Plants taken up :—

The plants have been almost stationary since the last report; termination of the
ascending axis keeps green; no indication of heading. (See Plate XV. fig. 1.)

Soil moist, soft, and spongy.

Roots not distributed generally throughout the soil; a few isolated ramifications

550 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

extended to the lower part of the pot; but the great mass remained near the base of the

stem. ‘Total quantity of root very small compared with that of wheat No. 6 manured

with ammonia-salts. For general character of root-development, see Plate XV. fig. 15.
For method of further treatment see pp. 543, 544.

No. 2.—Barley (1857) ; sia seeds; prepared soil ; without nitrogenous manure.
(See Plate XV. fig. 2.)

June 9.—Six plants; 2 to 3 inches high, with two fully developed leaves; tips of
some of the leaves slightly yellow.

June 15.—Three plants with three leaves, and three with two leaves each; tips of
lower leaves slightly yellow, but general appearance healthy.

June 24.—Plants 4 to 6 inches high, with three or four leaves each; much the same
condition as wheat No. 1 at this date.

July 4.—6 to 7 inches high, with four or five leaves; paler than wheat No. 1;
looking sickly. Drops of water on tips of leaves and inner surface of shade: see Note
thereon to wheat No. 1, same date.

July 11.—Lower leaves drying up; upper ones growing a little, apparently at expense
of the lower. Stems of these and the other barley plants reddish, and have been so
since the formation of true stems with nodes. The barleys form stem more readily than
the wheats, which are more leafy.

July 22.—Not much improvement. ,

July 29.—Only two small leaves at the top green; the amount green at one time
does not increase ; lower leaves dry up as new ones form.

August 10.—Very little change, except that one stem shows slight indications of
heading.

August 24.—Plants taken up :—

Six plants, 5 to 17 inches high, with six to nine leaves on each plant. Two indicate
slight tendency to heading, the sheath being swollen; but growth obviously ceased, the
two upper leaves having at last lost colour and driedup. On opening, one head showed
a rachis 2 inches long. The plant was very dry, so no fresh weight taken.

Prepared and analysed as described at pp. 543, 544.

No. 3.—Barley (1857) ; six seeds; prepared pumice ; without nitrogenous manure.
(See Plate XV. fig. 3.)

June 9.—Six plants, 23 to 4 inches high ; more developed, but more slender than the
barleys in soil (Nos. 2 & 8). Leaves turning yellow at the tips.

June 15.—Six plants, 6 inches high, each with three fully developed leaves; tips of
lower leaves dried up; middle leaves have yellow tips; upper ones pale green but
healthy. Plants appear to have almost done growing.

June 24.—Height about the same; three or four leayes each plant; lowest dried up,
next drying, and upper ones green.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 551

July 4.—Plants 6 to 7 inches high; five or six leaves each; upper leaves only pale
green.

[Drops of water collect as described in reference to No. 1 Wheat at this date.]

July 11.—Plants 6 to 8 inches high; five or six leaves each; upper ones green and
growing a little as the lower ones dry up; general aspect stationary.

July 22.—Very little growth.

July 29.—Plants 8 to 10 inches high, very slender, like mere threads; all lower
leaves dried up; upper ones | to 2 inches long and pale yellow. The six plants show
twenty nodes. Slight tendency to form very small heads.

August 10.—Plants quite dried up.

August 25.—Plants taken up :—

Six very slender plants, mere filaments, 8 to 20 inches long; with four to six nodes,
and six to eight leaves each. Stems zigzag at the nodes; leaves dried up and brown.
The top sheath of five of the plants indicates an excessively small head with zigzag
rachis, at the upper part of which is a well-defined husk but no seed; the lower parts
have beards and small rudimentary husks.

Preparation and analysis as described at pp. 548, 544.

No. 4.—Beans (1857) ; two seeds; prepared soil ; without nitrogenous manure.

June 9.—Two plants up; one 6 inches high, four leaves with two leaflets each and
two large stipules; the other smaller; both healthy and vigorous.

June 15.—One plant 73 inches high, with five leaves, each with two or three leaflets
and two stipules; the other 33 inches high, with four leaves and corresponding stipules.
Tips of some of the lower leaves slightly speckled, but the upper ones green, and both
plants healthy and vigorous.

June 24.—One plant 15 inches high, with seven leaves, each with two or three leaflets
and two stipules; lower leaves yellow, with dark specks at the edge, upper leaves and
stem light green; the other plant 9 inches high, four or five leaves with two to three
leaflets, &c., each; lower leaves as on the other plant, but upper ones greener. Plants
appear to have nearly done growing.

July 4—One plant 19 inches high; five leaves fallen off within two days, three
upper ones remain, these green, appear to live on nutriment drawn from the lower ones. .
The other plant 12 inches high, seven leaves, and a small sprout just at the surface of
the soil; lower leaves dead, upper ones nearly done growing.

July 5.—Plants taken up * :—

Preparation and analysis as described at pp. 548, 544.

* After removal of the beans, a barley plant from the field was potted with its own soil which was
comparatively dry, and placed under the shade without being watered, in order to see whether water was

given off and condensed within the glass as freely as in the case of the experimental plants. It was so;
and hence it was concluded that the experimental soils were not too wet.

MDCCCLXI. AF

552 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

No. 5.— Beans (1857); two seeds; prepared pumice; without nitrogenous manure.

June 9.—One plant 1} inch high, blackened, and dying; the other smaller and
already dead,

As will be seen by the records (p. 557), Beans Nos. 10 & 11 showed equally unhealthy
growth; all were therefore remoyed and re-planted. It was obvious that the failure
was too early to be due to want of available nitrogen; especially, as No, 4 Beans with a
similar amount of nitrogen lived. ‘The result was considered to be due to the caus-
ticity of the ash, as beans set in ash-free soil and pumice flourished much longer, and in
the case of No. 4 the seeds happened to be so placed as to be washed when water was
applied.

It was found on examination that all showed signs of recommencement of growth; new
roots and stems were forming. The seeds, &c. were remoyed; a little sulphuric acid added
to the soil (or pumice) to neutralize the ash, and it was then ignited as originally, put into
fresh red-hot pots, and cooled and moistened over sulphuric acid. Before putting in
fresh seeds, holes were made for them in the soil, and water poured in to remove soluble
matter from the neighbourhood of the young rootlets. The experiments were then
continued as before.

Report of No. 5 Beans continued.

June 24.—One plant just up.

July 1.—An accident occurred to this experiment. A fresh pot of soil, prepared
precisely as aboye, was planted with beans that had been set in small glass tubes ready
for any contingency, and the experiment continued.

July 4.—One plant, leaves just opening.

July 11.—Still only one plant up, and it looks very unhealthy.

July 22.—One plant, obviously dying.

July 29.—Dead.

No. 6.— Wheat (1857); three seeds; prepared soil; with nitrogenous manure.
(See Plate XV. fig. 7.)

June 9.—Two plants up; one 23, the other 43 inches high; three leayes each. Tips
of leaves slightly yellower than those of Wheat No. 1.

June 10.—A pipette-ful of the solution of sulphate of ammonia (=:00578 gramme N.)
added to the soil.

June 15.—Two plants; green and vigorous; marked improvement since the addition
of ammonia-salt ; the leaves wider and_of a deeper green. Three leaves each plant.

June 24.—Two plants; 7 inches high; four or five leaves each; lower ones dried up,
upper ones deeper green than Wheats No. 1.

July 4.—Two plants; 9 ches high; six leaves each; lower ones yellow, upper ones
broad, long, and of a healthy deep green; but the vigour due to the first addition of

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 553

ammonia appears to have ceased. Second pipette-ful of ammonia-solution (same quan-
tity) added.

July 11.—Two plants, 10 inches high; seven leaves each; upper ones deep green,
broad, and vigorous. Third pipette-ful of the ammonia-solution added.

July 22.—Growth vigorous ; shooting out at the base of the stems. Fourth pipette-ful
of the ammonia-solution added.

July 29.—Much greater tendency to form leaf than stem. One plant with four, and
the other with two subdivisions. 12 to 16 inches high, the height greatly due to the
length of the leaves. Not a single node clear of the sheath of the one below it; thus
essentially different from the barleys, which have great tendency to form nodes and stem.
Fifth pipette-ful of the ammonia-solution added.

August 10.—Green and flourishing.

August 24.—Plants 17 to 20 inches high; ten to twelve leaves on each; upper ones
long, broad, and green; lower ones dried up. But little tendency to form stem; leaves
larger than on plants in the field; some 12 inches long and 3} inch wide; no nodes clear ;
the leaves spring out so close together as to appear almost opposite. Five stems from
the two seeds.

October 2.—Plants taken up :—

One seed has given three strong and one small stem; another one stem; the third
did not grow. Leaves very numerous and close together, giving several thicknesses of
sheath around the stem, and hiding all the nodes; lower leaves dried up; upper leaves
and central axis of growth green. Condition nearly stationary for the last two or three
weeks. Average height of plants about 18 inches.

Soil quite moist throughout; also soft, and spongy, rather more so than the pumice
soils; a little water remained in the plate below the pot.

Roots much, but very irregularly distributed—a large bunch around the base of the
stem; small, long, isolated roots extended to the bottom and up the sides of the pot;
quite a mass of ramified roots over the bottom, and somewhat up the sides of the pot;
and a greater mass in the dish under the pot, forming a circular web the size of the
bottom of the pot. A crack in the bottom of the pot was penetrated with roots through-
out, showing, perhaps, that more openings than the one hole at the bottom might be
advantageous. For representation of the root-development, see Plate XV. fig. 14.

Preparation and analysis as described at pp. 648, 544.

No. 7.—Wheat (1857) ; three seeds; prepared pumice; with nitrogenous manure.

June 9.—Three plants up, 3 to 4 inches high; each with three leaves completely
formed, of which the tips are slightly yellower than those of Nos. 1 and 6, but no appear-
ance of diseased condition in any of the wheats.

June 10.—A pipette-ful of the ammonia-solution (=-00578 gramme N.) added to
the soil.

June 15.—Plants 5 to 6 inches high, with four leaves each; the tips of the lower

4p2

554 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

ones yellow; the newer and upper leaves green, healthy, and vigorous; marked im-
provement since adding the ammonia-solution on June 10, the effect of which was
manifest within two days after the addition.

June 24.—Plants 5 to 7 inches high, with four leaves each; lower leaves dried up,
but upper ones green and vigorous; obviously improving; forming stem with nodes.

July 4.—Plants 7 to 8 inches high, with five to seven leaves each; the newer ones
broad, well developed, and of a deep green colour; upon the whole vigorous. Second
pipette-ful of the ammonia-solution added.

[Drops of water accumulate as described in reference to No. 1 of this date. ]

July 11.—Plants 8 to 9 inches high, with six or seven leaves each; lower ones pale
yellow, upper ones green and vigorous. One of the stems sending out a shoot at its base.
Third pipette-ful of ammonia-solution added.

July 22.—Growing very well; tillering very much. Fourth pipette-ful of the ammonia-
solution added.

July 29.—Plants 12 to 16 inches high; one with six shoots 4 to 8 inches long; one
with one shoot 3 inches long; and the other with two shoots just forming; shoots, and
upper leaves, green. The ammonia seems to induce multiplication of shoots instead
of upward growth; no nodes clear of the sheath. Fifth pipette-ful of the ammonia-
solution added.

August 10.—Green and flourishing.

August 24.—Very similar to Wheat No. 6 at this date.

September 20.—Plants taken up :—

The lower leaves begin to lose colour considerably, no increase of growth apparent for
some days, nor any tendency to form seed; hence, the season being far advanced, the
plants taken up.

Great development of root; the plate under the pot covered with a dense network
ramified from a few fibres extended to the bottom of the pot; a similar network at the
bottom and partially up the sides within the pot; comparatively little in the centre of
the soil.

Preparation and analysis as described at pp. 543, 544.

No. 8.—Barley (1857); four seeds ; prepared soil; with nitrogenous manure.
(See Plate XV. fig. 8.)

June 9.—Three plants up; two 13 inch and one 33 inches high; colour pale.

June 10.—A pipette-ful of ammonia-solution (=*00578 gramme N.) added to the soil.

June 15.—Three plants; about 43 inches high; each with two ‘leaves and another
forming. Improved by the ammonia added June 10, but not so much as the Wheat
No. 6.

June 19-20.—During thenight the shade was cracked, from the bottom in the quick-
silver, 9 inchesupwards. ‘The pot with its contents was removed and put under a shade
over sulphuric acid. After four days it was returned to its place, and covered with the

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 555

shade of Experiment No. 12 (with plants in garden soil), the latter being replaced by
the damaged shade after the crack had been mended with strips of bladder cemented
with albumen and lime-water. All the circumstances of this accident were carefully
considered, and it was concluded that no appreciable error could arise from it.

June 24.—Three plants, 3 to 5 inches high; three or four leaves each; lower ones
dried up, upper ones pale green; plants slender, but improved since the addition of the
ammonia-solution.

July 4.—Plants 6 to 7 inches high; five leaves each; the most delicate and slender of
the plants that have had ammonia-solution ; upper leaves darker green than those with-
out ammonia; lower leaves yellow. Second pipette-ful of ammonia-solution added.

[The same remarks apply here, as were made to No. 1 at this date, in reference to con-
densation of drops of water. ]

July 11.—Plants 7 to 9 inches high; six or seven leaves each; stem reddish; upper
leaves healthy and deep green. Third pipette-ful of ammonia-solution added.

July 22.—Growing vigorously. Fourth pipette-ful of ammonia-solution added.

July 29.—Four plants, 16 to 20 inches high. Since the last two additions of
ammonia-solution, two of the plants have sent out at the base two new shoots, 6 to 8
inches high; one, two new shoots 2 to 4 inches high; and the other, one shoot. All
these shoots are deep green and growing vigorously. A great tendency to develope new
foliage; and though some of the stems were just beginning to swell, indicative of head-
ing, and one showed a beard, yet this growth was arrested, and the energies of the plant
directed to the new growths at the base. In all, seventeen nodes clear of the sheaths.
Fifth pipette-ful of the ammonia-solution added.

August 10.—Since the last three additions of ammonia the old stems ceased to develope,
but some of the new ones are on the point of heading.

August 24.—Kight plants from the three seeds. One seed has given one plant 24
inches high, with seven nodes clear, and nine leaves, of which the seven lower ones are
dried up; the plant terminated by a well-formed head. Another seed has four stems,
16 to 20 inches high; one dried up just as it was heading; the three others green and
healthy, and two just commencing to head; each stem four to six nodes, and six to ten
leaves. The third seed has three stems 12 to 24 inches high, each with three to five
nodes and five to ten leaves; one stem dried up.

October 8.—Plants taken up :—

Fight stems from three seeds, as under :—

(a) Seed with one stem; 18 to 20 inches high; seven nodes. ‘This was the first plant
that headed ; all ripe and dry; six glumes, containing only rudimentary or undeveloped
seeds.

(4) Seed with three stems. One 17 inches high; head ripe, and rather decaying.
Another 25 inches high; grown several inches, and formed head, since August 24; head

green, with five soft milky unripe grains. The third stem green at top, and upper
sheath swollen with the head.

556 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

(c) Seed with four stems:—(1) 22 to 23 inches high, with green head and six unripe
grains; leaves dry and ripe; (2) stem 15 inches high, dried up, head-sheath formed ;
(3) 19 inches high; yellowish-green head, with nine glumes, and undeveloped seeds;
(4) about 15 inches high; rather green, sheath swollen, and beard appearing.

During the last three weeks some heads came out more, and indications of others
developed; otherwise not much change. From the low temperature and lateness of the
season, it was thought the plants would not mature further.

Preparation and analysis as described at pp. 543, 544,

No. 9.—Barley (1857); four seeds ; prepared pumice; with nitrogenous manure.
(See Plate XV. fig. 9.)

June 9.—Four plants; one quite small; the others 3 to 4 inches high. These more
grown than the Barley plants Nos. 2, 5 & 8; but the leaves, particularly the lower ones,
yellower at the ends.

June 10.—A pipette-ful of ammonia-solution (=:00578 gramme N.) added to the
soil.

June 15.—Four plants; 5 to 6 inches high; four leaves each; lower ones losing
vitality. Lower leaves were too far gone, but a most marked improvement in the
upper ones since the ammonia-salt was added ; it was manifest in two to three days after
the addition.

June 24.—Four plants; height 6 to 8 inches; improved very much by the addition
of the ammonia-solution.

July 4.—Plants 8 to 13 inches high; six or seven leaves each; stems very slender,
but show well-formed nodes. Second pipette-ful of ammonia-solution added.

[Drops of water accumulate as described in reference to No. 1 of this date. }

July 11.—Plants 9 to 14 inches high; seven or eight leaves each; upper ones
deep green; lower ones yellow; stems red. Third pipette-ful of ammonia-solution
added.

July 22.—Growing very well; showing indications of heading. Fourth pipette-ful of
ammonia-solution added.

July 29.—The four plants all out in head; about 30 inches high; each stem six
nodes; two of the plants have shoots 5 inches high. ‘The ammonia seems to tend more
to new growth than to the development of the old.

August 10.—Heads well developed.

August 24.—The plants appear to be ripening; heads turning brown; but one new
stem is still green and growing.

September 24.—Plants taken up :—

Seven plants; five 2 to 23 feet high, one green; one 1} foot high, green head; one
14 inches high, green. Six with heads, four ripe and two green; the shortest plant
with green leaves and without head. Heads 1} inch long; glumes all along the rachis,
but only some with grains.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 557

Roots by no means so abundant as those of Wheat with ammonia-salt; only a few
fibres extended through the hole at the bottom, or to the sides of the pot.
Preparation and analysis as described at pp. 543, 544.

No. 10.—Beans (1857); two seeds; prepared soil ; intended to have nitrogenous manure.
June 9.—Only one plant up; 2 inches high; turning black and obviously dying.
For particulars of taking up, setting fresh seeds and recommencement of the experi-

ment, see remarks made on June 9 to Bean No. 5, p. 552.

June 15.—Not yet up.

June 24.—Two plants just appearing.

July 4.—Two plants well up and growing; leaves just opening.
July 11.—Two plants; 6 to 8 inches high; leaves deep green.
July 22.—Green, healthy, and vigorous.

July 29.—Nearly as at last date, but somewhat declining.
August 10.—Obviously dying.

August 24.—Dead.

The season too far advanced to repeat this experiment.

No. 11.—Beans (1857); two seeds; prepared pumice; intended to have nitrogenous manure.

June 9.—One up; slender; black spots on the leaves; obviously unhealthy. Taken
up, and the experiment recommenced ; for particulars of resetting, &c., see remarks to
Bean No. 5 of this date, p. 552.

June 15.—Not yet up.

June 24.—Two plants just up.

July 11.—Apparently not going to grow.

July 22.—Dead; the season too far advanced to repeat this experiment.

No. 12.— Wheat, Barley, and Beans (1857); Wheat and Barley three seeds each, Beans
two seeds; in rich Garden soil. (See Plate XV. fig. 13.)

May 18.—Seeds of wheat, barley, and beans, all sown together in a single pot of
good garden soii, and placed under a shade (No. 12), to be supplied with washed
air, &c., just as in the other experiments. The seeds germinated well.

May 28-29.—During the night, owing to a leakage of water from the reservoir into
the vessel A (see description at p. 476 et seg., and Plate XIII.), it passed over into the
sulphuric acid and carbonate of soda wash-bottles, and the mixed liquid passed into the
shade to the depth of some inches, and destroyed the experiment.

May 30.—Plants from seeds which had been set at the same date as the foregoing,
were transplanted into a fresh pot of garden soil, which was placed under the shade,
and the experiment recommenced. The wheat and barley plants were about 5 inches,
and the beans about 4 inches high.

June 15.—Healthy, and growing vigorously.

June 24.—Three wheats, three barleys, and two beans. Wheat 14 inches, barley

558 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

13 inches, and beans 11 inches high. Wheat and barley much branched at the base,
giving fourteen stems from the six seeds; all a deep green colour. Beans deep green,
and growing well, excepting that one has a few black specks on the lower leaves. So
much growth that the plants are considerably crowded in the shade.

July 4.—Much crowded. Graminaces 20 inches, Leguminosw 15 inches high. ‘The
former growing as well as in the open air. The latter appear to suffer from crowding ;
their lower leaves dying.

July 12.—The Graminacee growing very healthily; Leguminose apparently not so.

July 22.—The Graminacee growing vigorously ; Leguminose revived, and also grow-
ing vigorously at the top. During the last few days they have been protected from the
direct sun by a sheet of paper tied round the shade.

July 29.—Four barleys in head; wheat not so advanced, but nearly as high; the
beans had again suffered, but one is recovering. Too much crowded.

August 10.—About as at last date.

August 24.—About as at last date; barley slowly ripening.

The object of the experiment being attained, which was to determine whether the
conditions of atmosphere were suited to healthy growth, provided the soil supplied
sufficient nutriment, no further records of growth were made.

II. Pants grown in 1858*.

As in the experiments of 1857, so in those of 1858, the plants grown may be divided
into two Series, as under :—

Series 1. With no other combined Nitrogen than that contained in the seed sown.

Series 2. With a supply of known quantities of combined Nitrogen beyond that con-
tained in the seed.

The notes of growth of the plants grown without any extraneous supply of combined
nitrogen are given first, and then those of the plants grown with such supply. As
before, in several experiments instituted with Leguminous plants they died before
attaining a sufficient amount of growth to render it of any use to analyse the products.
The records of their progress, such as it was, are, nevertheless, shortly given.

No. 1.—Wheat (1858) ; eight seeds; prepared soil; without nitrogenous manure.
(See Plate XV. fig. 4.)

April 27.—Seeds set, and the pot placed under a shade over sulphuric acid.

May 7.—All the plants up; the pot removed to its shade on the stand.

May 20.—Eight plants; all of a healthy green colour; seven 4 inches high, one just
above the soil.

* The figures (Plate XV.) of the plants grown in 1858 are reduced from drawings taken, in most cases,
not many days before the plants were taken up.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 559

May 22.—A pipette-ful of the sulphuric-acid solution added.

May 29.—Kight plants, 4 to 6 inches high; each -with four leaves, the two lower
yellow, the two upper green and healthy. A drop of water appears on the tip of the
upper leaves in the morning, but it disappears before midday, as the air is passed
through the shade. A pipette-ful of the phosphate-solution added.

June 7.—A pipette-ful of the phosphate-solution, and a pipette-ful of the sulphuric-
acid solution added.

June 19.—Plants 5 to 7 inches high; two lowest leaves on each dried up; upper
ones yellowish green.

June 26.—Eight plants, 6 to 7 inches high; six leaves each, three lower ones dried
up, next two pale green, only upper central one green and healthy. Apparently at
limit of growth without more combined nitrogen; very much as last year without
nitrogenous manure.

July 3.—A pipette-ful of the phosphate-solution, and a pipette-ful of the sulphuric-
acid solution added.

July 14.—Plants 6 to 8 inches high, with six or seven leaves each; only the two
upper ones yellowish green; apparent stagnation of growth.

July 29.—Much as last; two upper leaves seem to sustain life at the expense of the
rest.

August 17.—After long inactivity several plants show tendency to grow in stem. In
this, somewhat more like the barley than wheat of last year. Some disposition to
heading.

September 7.—Still developing stem ; nodes and internodes distinctly marked. Plant
(a) 13 inches high, ten leaves, three nodes bare, slightly swelled at top as if heading ;
new stem-leaves, only 2 to 3 inches long. Plants (6 and ¢) 9} inches high, nine leaves,
two or three bare nodes; slight indication of heading. Plants (d, e, and f) 73 inches
high, two bare nodes; stems shorter, leaves eight or nine, a little longer than above.
Plant (7) two branches; the first short, and dried up; a new one formed from its base,
green, but only 4} inches high, with four green leaves. Plant (/), dried up stem with
three long leaves; but a new green shoot with two leaves, though little growth.
General remark :—all lower and first-formed leaves dried up, the next yellowish, and
only the two upper ones green. Drops of water collect at the tips, and axils, of the
green leaves. The later growth obviously at the expense of the earlier.

October 5.—Little change, except riper. Plant (a) 14 inches high, eleven leaves,
nearly all dried up, four bare nodes, a head with indications of seeding: (2) 103 inches
high, eleven leaves, all ripe but the uppermost, three bare nodes, and indication of
heading: (c) 9} inches high, nine leaves, three nodes: (d and e) 8} inches high, eleven
leaves each: (f and g) 4 to 7 inches high, dead stems with eight to ten leaves each,
but green shoots at the base: (h) 7 inches high and seven leaves, dead ripe.

October 24.—Weather much warmer again lately, and slight renewal of growth;
drops of water again appear on the green top leaves. The chief growth is further deve-

MDCCCLXI. 46

560 MK. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

lopment of the rudimentary head; a definite rachis formed, with joints and rudimen-
tary husks, but no indication of seed.

October 25.—Plants taken up :—

Soil quite wet, loose, and open, to the bottom; roots pass through the pot at nearly
all the bottom holes, and at some of the side ones; long roots distributed among the
flints; very few roots come to the sides of the pot (see Plate XV. fig. 17).

Plant 1. Dead ripe, 7 inches high, seven long leaves, one dead shoot; roots long,
apparently going to the bottom, very little distributed.

Plant 2. Seven inches high; two stems; one with six leaves, dead ripe; the other with
three leaves, one still slightly green; no nodes visible; each, a moderate amount of root.

Plant 5. Eight inches high; ten leaves, lower long and dead, two upper green; no
nodes visible. Many roots at the base, some extending downwards. Roots of this and
all the plants have short forked branches, } to 4 inch long, blunt and thick, and gene-
rally forked at the end; strikingly different from the roots among the loose flints at
the bottom, and those under the pot.

Plant 4. Height 103} inches; thirteen leaves; six visible nodes; slight swelling at the
head. Fewer roots branched and distributed in the soil near the base of the stem; most
go to the bottom, or even under the pot, thus taking nutriment from the water in the
dish rather than from the soil ;—perhaps associated with this the superior growth over
plants 1, 2, and 3.

Plant 5. Very similar to No. 4.

Plant 6. Very similar to Nos. 4 and 5; but the head rather more developed, and
visible through the transparent sheath, and the roots with rather more the character of
pot or soi roots.

Plant 7. Eleven inches high; twelve leaves; five nodes visible; head with chaff with-
out grain, and beard # inch long; rachis 1 inch long. Roots but little branched, going
down and developed more at the bottom and in the dish than in the soil.

Plant 8. The largest and most developed plant. Fourteen inches high ; twelve leaves ;
lower ones long and crowded, upper ones shorter and further apart (as in all); four nodes;
head with rachis 1} inch long, with glumes and pales. Roots very similar to No. 7,
forming under the pot a thick matted mass, running round the dish, some of which, when
untangled, are 3 to 4 feet long; white, transparent, and with many small thread-like
branches; the whole somewhat resembling a mass of white thread.

Preparation and analysis as described at pp. 543, 544.

No. 2.—Barley (1858); eight seeds; prepared soil; without nitrogenous manure.
(See Plate XV. fig. 5.)
April 27.—Seeds set, and the pot placed under a shade over sulphuric acid.
May 7.—Pot removed to its shade on the stand.
_ May 20.—Five plants 4 inches high, and one 1 inch. Were at first quite green and
healthy, but the last few days turing yellowish green.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 561

May 22.—A pipette-ful of the sulphuric-acid solution added.

May 29,—Five plants 4 to 5 inches high, with three or four leaves each ; lower ones
yellow and dried up; upper pale yellowish green. A sixth plant, smaller. A pipette-ful
of the phosphate-solution added.

June 7.—A pipette-ful of the phosphate-solution, and a pipette-ful of the sulphuric-
acid solution added.

June 19.—One plant dead; two about 4 inches high with shoots at the base; other
two about 8 inches high.

June 26.—Plant (az) dead; cause not obvious. Plant (6) 10 inches high; as last year,
forming stem well. Plant (¢) 8 inches high. Plant (d) a main stem which is dead,
and a new shoot which is green (each 3 to 4 inches high). Plant (e) a good deal like (d).

July 3.—A pipette-ful of the phosphate-solution, and a pipette-ful of the sulphuric-
acid solution added.

July 14.—Plant (4) 9 to 10 inches high ; six dried up, and two green leaves ; swelling
apparently for heading. Plant (c) about 7 inches high; seven dried up and two green
leaves. Plant (d) two stems 4 to 6 inches high; six dried up and two green leaves.
Plant (e) two stems 4 to 6 inches high, with five dead and two green leaves.

The upper leaves quite short (1-1} inch long), and apparently live at the expense

of the lower.
_ July 29.—Plant (a) dead; six leaves, becoming brown-yellow; a black mildew has
attacked the leaves and stem; and a white gossamer-like fungus has attached itself in
places to the stem and leaves. Leaves 3+ to 4 inches long; the upper thread-like and
drooping. Plant (4) the most flourishing; 14 inches high; but very spindly; six nodes,
which, with portions of the adjoining culm, especially the upper part, are dark purplish ;
eight leaves; lower ones yellow, and the lowest two, which are in contact with plant
(a), affected with the mildew; all but the uppermost leaf 2 to 24 inches long; the upper
one 13 inch long, pale green, and quite erect, apparently the last effort of the plant, no
new leaves forming. Plant (c), divided just beneath the soil into three shoots; two
apparently suckers from the other, each 3 inches high, and dead. The main plant
6 inches high; has seven leaves; the four lower dead, and the three upper, making up’
half the plant, pale green; the uppermost only } an inch long, in the fold of the second.
Only one node visible; the culm, where seen, is purplish. The white fungus occurs, but
no mildew. Plant (d) much like the main plant (¢); evidence of early effort to put out
shoots at the base. ‘Twelve leayes; ten lower ones dead; two upper ones living; all
2 to 24 inches long. Plant (e) the second in size. Eleven inches high; ten leaves;
eight lower ones dead, two upper ones living; all erect but the lowest two; each 2 to
3 inches long.

August 18.—Plants taken up :—

Eyidently done growing ; four stems swelled for head; all leaves except the uppermost
dried up. Roots not much distributed; general characters much like those of barley
without nitrogenous manure last year (1857). Soil moist, loose, and open.

Preparation and analysis as described at pp. 543, 544.

462

562 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON
No. 3.—Oats (1858) ; eight sceds; prepared soil; without nitrogenous manure.
(See Plate XV. fig. 6.)

April 27.—Seeds set, and the pot placed under a shade over sulphuric acid.

May 7.—The pot removed to its shade on the stand.

May 22.—A pipette-ful of the sulphuric-acid solution added.

May 29.—Kight plants, 4 to 6 inches high; four or five leaves each; lower ones
yellow, upper ones green and growing. These Oats growing rather better than either
No. 1 Wheat, or No. 2 Barley. <A pipette-ful of the phosphate-solution added.

June 7.—A pipette-ful of the phosphate-solution, and a pipette-ful of the sulphuric-
acid solution added.

June 19.—Fight plants, 6 to 9 inches high; five or six leaves each, lower yellow and
dead, upper green. ‘Tips of some of the leaves injured by action of direct sun-rays.

[General note-—White paper had been tied over all the shades to screen from the
direct rays of the sun; but in this case not quite high enough. }

June 26.—Kight plants; five 10 to 11 inches high, and in head; three 8 to 9 inches
high; no appearance of heading, and two of them a green shoot at the base. Six or
seven leaves on each plant. The rachis of the seeding plants long and crooked, with
one or two seeds at top, without signs of seed below. All the plants apparently at
termination of growth; remain only to see how far they will ripen.

July 3.—A pipette-ful of the phosphate-solution, and a pipette-ful of the sulphuric-
acid solution added.

July 13.—Plants taken up :—

Eight plants, quite dead ripe for some days, having had a hot sun.

Plant (1) 133 inches high; five leaves; rachis 1} inch long, with one seed. Plant (2)
113 inches high ; five leaves; rachis1} inch. Plant (3) 12}inches high ; five leaves; rachis
13 inch long, with two seeds. Plant (4) 123 inches high; with shoot appearing at base ;
rachis 14 inch long, with two seeds. Plant (5) 113 inches high; five leaves; with shoot
appearing at base. Plant (6) 9 inches high; five leaves; and shoot at the base, 4 inches
long. Plant (7) 10 inches high; five leaves; and shoot at the base 4incheslong. Plant
(8) 103 inches high; five leaves; rachis 13 inch long, two seeds. Roots only extended
about 2 inches deep in the pot. Soil wet and soft; the lower part firm, but not hard.

Preparation and analysis as described at pp. 543, 544.

No. 4.— Beans (1858) ; three seeds; prepared soil; without nitrogenous manure.

April 27.—Seeds set, and the pot placed under a shade over sulphuric acid.

May 20.—Pot removed to its shade on the stand. Three plants up, 2} inches high ;
three leaves on each; dark green and healthy.

May 22.—A pipette-ful of the sulphuric-acid solution added.

May 29.—Plants 3 to 4 inches high; one looks to be dying; the others have specks
on their leaves. A pipette-ful of the phosphate-solution added.

June 7.—A pipette-ful of the phosphate-solution, and a pipette-ful of the sulphuric-
acid solution added to the soil. °

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 563

June 19.—One plant dead; another looking unhealthy; the third 4 to 5 inches high,
with five leaves, growing pretty well.

June 26.—Two plants dead; the other growing, 7 to 8 inches high, with nine leaves,
each with two stipules.

July 3.—A pipette-ful of the phosphate-solution, and a pipette-ful of the sulphuric-
acid solution added.

July 14.—The third or only surviving plant has ten leaves, but looks unhealthy.

July 29.—The two dead plants fallen, moulded, and dried up. The other blackened
and mouldy at the base of the stem, and thence to the top yellow; three top leaves
partly yellow, but the remainder black.

August 17.—All three entirely dead. Pot removed, but products not analysed, as
there had not been sufficient healthy growth. It is difficult to account for this failure;
but it is possibly due to the very hot weather.

No. 5.—Beans (1858); three seeds; prepared soil; without (but intended to have)
nitrogenous manure.

June 11.—Seeds set in prepared soil, with ash that had been neutralized with sul-
phuric acid, and gently re-ignited; and the pot placed over sulphuric acid and covered
with a glass shade.

June 21.—The pot removed to its place on the stand.

June 26.—Three plants up; green and healthy; four leaves, each with two leaflets,
and two stipules. Plants delicate, but healthy green colour; one shows air-roots.

July 3.—A pipette-ful of the phosphate-solution, and a pipette-ful of the sulphuric-
acid solution added.

July 14.—Three plants, healthy and vigorous; 8 to 12 inches high; eight leaves on
each; a few black specks on some of the leaves, otherwise healthy. The weather has
been comparatively cool since planting till now; but now hotter with bright sun. A
few air-roots at the base of the stems.

July 29.—Three plants ; 8, 83, and 12 inches high. Plant (a) lost all its leaves, except
rudimentary ones at the top. A shoot 2 inches long with four small leaves about an
inch from the base, more growing than the parent plant; another shoot appearing about
an inch above. Plant (d) very unhealthy; lost all leaves but six small and partly black
ones at the top; a vigorous shoot 5 inches long, springing an inch from the base, seems
to exhaust its strength; another small shoot 1 inch long, about 2 inches higher up.
Plant (¢), most of the leaves dropped; but several of the petioles remain, and are green ;
some small withering leaves at the top; two shoots starting near the base.

August 17.—Three plants; the main stem of each lost nearly all the leaves. Each
plant has living shoots with several leaves each near the base. ~

August 23.—Plants taken up :—

There has been scarcely perceptible growth for two or three weeks; leaves nearly all
off. Soil moist. Roots extend only a little way, and consist of a thick mat around the

MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

564
base, much divided; none reached the flint; the upper ones dead, the lower living; less

root than last year.
Preparation and analysis as described at pp. 543, 544.
No. 6.—Pea (1858); three seeds; prepared soil; without nitrogenous manure.
Three more set to-day in prepared soil, with

June 5.—Three peas previously set died.
ash that had been neutralized with sulphuric acid, and gently re-ignited; and the pot

placed over sulphuric acid and covered with a glass shade.
June 7.—A pipette-ful of the phosphate-solution, and a pipette-ful of the sulphuric-

acid solution added.
June 19.—Pot removed to its place on the stand.
June 26.—Three plants, 6 to 7 inches high, with four leaves each ; not growing well.
July 3.—A pipette-ful of the phosphate-solution, and a pipette-ful of the sulphuric-

acid solutiog added.
July 14.—Three plants; doubtful whether they will live.
July 29.—Three plants ; two 6 inches, and one 7 inches high; apparently dead some
days, yellow, and a few spots of mould.
August 24.—Plants taken up :—
All dead for some time past; probably owing to the heat. Products submitted to
analysis, but the results can only be of confirmatory value.
No. 7.—Buckwheat (1858) ; seed, 1 gramme ; prepared soil ; without nitrogenous manure.
August 20.—Seed sown, and the pot placed over sulphuric acid, and covered with a

glass shade.
August 24.—Removed to its shade on the stand. Several plants up.

September 7.—Gyrowing well.
October 5.—Sixteen plants, 2 to 4 inches high, four to six leaves each.
October 24.—Eighteen plants, 3 to 4 inches high, with four to six leaves each; leaves

4 to $ inch wide, but have begun to look yellow and curl up; some plants dead. The
plants appear to have attained their maximum growth without nitrogenous manure.
October 28.—Plants taken up :—
Eighteen plants with four to six leaves each, including the seminal opposite ones; 2
to 3 inches high ; obviously done growing; only five or six with green leaves remaining.
Roots only 2 to 3 inches long, slim, delicate, and very little distributed. Soil quite

loose, porous, and friable.
Preparation and analysis as described at pp. 543, 544.
No. 8 (1858).—PLants GRowN wiTHout NitroGENnous Manure IN M. G. ViLe’s Casz*.

M. Vite kindly forwarded porous pots, and glazed white pans to set them in, such

* The experiments conducted in M. G. Vrnxn’s cases were commenced later in the season than those
with the shades, as we waited some time in the hope that M. Vixux might be able to come over and super-

intend the arrangement himself.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 565

as he used in his experiments; but as too many were broken in transit to use these
entirely, it was decided to use pots and pans the same as for our other experiments in
1858. The soil, ash, &c., were also prepared in the same way as for the other expe-
riments of 1858—the ash, however, being saturated with sulphuric acid and re-ignited
before being used, as in a few only of the other cases; for description, see pp. 470-472.

Pot 1—Wheat; eight seeds.

Pot 2—Barley; eight seeds.

Pot 3—Oats; eight seeds.

Pot 4—Beans; three seeds.

June 11.—Wheat, Barley, and Oats; seeds set, and the pots placed over sulphuric acid,
and covered with a shade.

June 12.—The three pots removed to M. VILLE’s Case.

June 19.—Wheat, Barley, and Oats all up, and looking green and healthy.

June 25.—Cereals all about the same size, with three leaves each; wheat quite pale,
barley and oats green at the top, and lower leaves dead.

The Case was opened, and the pot of three beans put in.

July 1—Wheat pale and blanched; barley and oats, lower leaves dead, upper ones
green and growing.

July 8.—AlIl the Cereals getting quite pale; beans healthy.

July 14.—Bean, three plants up; two cotyledons and two leaves on each, healthy.
Wheat, seven plants; 4 to 6 inches high; four leaves on each, upper green, lower dead.
Oats, seven plants; very like the wheat; but little more disposition to form stem.
Barley, eight plants; much like the oats. :

August 2.—Beans, 4 inches high; lower leaves dead, and show a white mould; small
stems putting out languidly. Barley, eight plants; 4 to 5 inches high; lower leaves
yellow and dead; upper blades green; stems appear mouldy. Oats, seven plants about
5 inches high; lower leaves dead and mouldy; upper part of stem green, and slightly
swelled as if going to head. Wheat, very much like the barley.

August 17.—Cereals appear to have nearly done growing; beans dying.

September 7.—Beans dead. Wheat green at the tops, but dead below; 4 to 6 inches
high; about ten leaves each. Oats nearly dead. Barley nearly dead.

October 24.—Wheat still green at the top; oats and barley dead. Beans dead (not
analysed).

November 6.—Plants taken up. Notes as under :—

Wheat. Seven plants; 4 to 5 inches high; no nodes visible; little tendency to form
stem; lower leaves dead; top leaf green, and on some the next greenish yellow. Soil
moist. Very little root.

Oats. Seven plants, 4 to 6 inches high; about six leaves each; generally four nodes
visible; most forming head. Roots but little distributed; very little below 14 inch;
fewer and more slender than those of the wheat. All the plants dead or ripe, but not
decomposed; the stems firm and elastic.

Barley. Fight plants, 4 to 6} inches high; two to four nodes visible in all; six or

566 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

seven leaves on each; most have a leaf-like heading stretching upwards; lower leaves
generally very long, 4 or 5 inches. Roots very little distributed; perhaps a little deeper
than the oats; but few deeper than 1} to 2 inches. Soil dry, loose, and porous; flints
quite open. '

Wheat, Oats, and Barley prepared and analysed as described at pp. 543, 544.

Plants grown in 1858, with a supply of combined Nitrogen beyond that contained in the
seed sown.

No. 9.— Wheat (1858) ; four seeds; prepared soil; with nitrogenous manure.
(See Plate XV. fig. 10.)

April 27. Seeds set, and the pot placed over sulphuric acid, and covered with a glass
shade.

May 20.—Four plants up; healthy, green, and growing; about 4 inches high; very
similar to Wheats No. 1 of this date.

May 22.—A_ pipette-ful of the sulphate-of-ammonia solution (=0°004 gramme N.)
added to the soil.

May 29.—F¥our plants, from 4 to 6 inches high. Greener and fresher since the
addition of the ammonia-solution ; new shoots appearing; only the lowest leaf on each
yellow. A pipette-ful of the phosphate-solution added.

June 7.—Second pipette-ful of the sulphate-of-ammonia solution added; and a
pipette-ful of the phosphate-solution.

June 19.—Four plants; one with four shoots or stems, and two others with two stems
each; in all nine stems or plants; 5 to 7 inches high; leaves more healthy, green and
vigorous.

June 21.—Third pipette-ful of ammonia-solution added. Plants had begun to show
the want of available nitrogen.

June 26.—Fourth pipette-ful of the ammonia-solution added. As intimated May 29,
the ammonia tends much to new shoots from the base. The four seeds have given—
No. 1, ‘one stem, with seven leaves: No. 2, two stems, each with six leaves: No. 3, three
stems, each with five or six leaves: No. 4, four stems, with four, five, or six leaves each: in
all ten stems. The two lowest leaves dead, the others green and vigorous. More vege-
table matter from these four seeds, with ammonia, than from the eight (No. 1 Wheat)
without it. Plants 8 to 11 inches high, and improve with each addition of ammonia.

July 1.—The shade slightly cracked at the bottom during the night, but still sufii-
ciently air-tight for changes of temperature to affect the level of the sulphuric acid in the
bulb-apparatus. Shade replaced by a small one temporarily. An immaterial amount
of condensed water lost. Many roots found to be distributed through the bottom of
the pot, and growing in the dish beneath it.

July 3.—Fifth pipette-ful of ammonia-solution added. [It is intended that none of
the plants shall suffer so much for want of combined nitrogen, asin 1857.] Also a
p:pette-ful of the phosphate-solution added.

July 12.—Sixth pipette-ful of ammonia-solution added.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 567

July 14.—Seventh pipette-ful of ammonia-solution added. Details of growth from
the four seeds as follow :—

No. 1, one stem only, 8 to 10 inches high; three upper leaves green and vigorous,
four lower yellow. No. 2, three stems: (a) 3 to 4 inches high, two yellow and two green
leaves; (2) 4 to 6 inches high, two yellow and two green leaves; (¢) 12 to 14 inches
high, three yellow and three green leaves. No. 3, three stems: (a) 4 to 6 inches high,
two yellow and two green leaves; (2) 8 to 10 inches high, two yellow and three green
leaves; (c) 13 to15 inches high, two yellow and three green leaves, No. 4, four stems,
8 to 10 inches high, three yellow and three green leayes each.

The “ yellow” leaves are small ones at the base, developed before ammonia was added,
and are dead. The ammonia strikingly developes the new shoots, and their leaves are
much larger. As last year, much more tendency to form leaf than run to stem. The
height given above includes that of the erect leaves extending above the ascending axis,

July 19.—Kighth pipette-ful of ammonia-solution added.

July 29.—Ninth pipette-ful of ammonia-solution added. The following details will
show how dependent is the development upon the proximity to the mouth of the tube by
which the ammonia-solution is applied,

No. 1 (furthest from the tube), one stem strong and vigorous at the base, and 13 inches
high. No. 2 (third from the tube), three stems; one 12 to 13 inches high, the others
smaller. No. 3 (second from the tube), five stems; three 12 to 15 inches high, and two
new ones 1 to 2 inches high. No. 4 (nearest the tube), seven stems ; four 8 to 13 inches
high, and three new ones 1 to 3 inches high.

All upper leaves green and vigorous, most of the lower yellow and dead; some of the
shoots entirely green.

August 10.—Tenth pipette-ful of ammonia-solution added.

August 17.—Eleventh pipette-ful of ammonia-solution added (a new solution, the
pipette-ful =0:00359 gramme N.).

Recently, much more disposition to form stem; several plants from 18 to 30 inches
high ; nodes clear of the sheaths. Comparing with the Wheat without ammonia, which
also tends more to stem of late, it appears that the amount of growth is due to the supply
of combined nitrogen, and its character (stemmy) more to the season.

August 26.—Twelfth pipette-ful of ammonia-solution added.

September 7.—Thirteenth pipette-ful of ammonia-solution (the last application ; in all,
0:0508 gramme N.) added. Growth from each seed as under :—

No. 1 (furthest from the ammonia-solution tube), one stem 23 inches high; twelve
leaves ; two nodes clear; slight indication of heading.

No. 2 (third from the tube), one main stem growing, and two shoots dead; main stem
23 inches high; three upper leaves green, six lower ones yellowish; not heading yet.

No. 3 (second from the tube), three stems; two like “No, 2”; the third 12 to 14
inches high ; little tendency to form stem, but long leaves from the axis.

No. 4 (nearest the tube, some of the roots washed when the solution, or water, is
MDCCCLXI. 4u

568 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGIL ON

added), two stems and five small shoots:—(a) highest leaf touches the top of the shade,
and 3 inches of it lie against the wet glass, by which it is injured ; ten leaves; three bare
nodes; (6) 23 inches high; nine leaves, three upper green, others yellowish; nodes not
clear of the sheath; not heading yet; (c) three small stems from the base, 6 to § inches
high, ceased to grow, and apparently dying; (d) two small rudimentary shoots; ceased
to grow, and dying.

Main stems—lower leaves yellow or dead; those starting a few inches from the soil
numerous, and 12 to 16 inches long; those higher up, 4 to 6 inches long, green, and
healthy; apparently incapable of supporting all the shoots started.

October 5.—Plants principally increasing in height of stem; three touch the top of
the shade; upper leaves green. Shaded from the direct sun to prevent injury from the
little aqueous lenses formed on the interior of the shade; yet sun apparently wanted
for ripening.

October 24.—Shade entirely full of vegetable matter, some stems touching the top,
and leaves touching on all sides. Season for growth about over; plants seemed stationary
during some recent cold weather, but, the last few days being warmer, they have revived
again. [This remark applies to all the Cereals. |

October 26.—Plants taken up; produce from each seed as under :—

No. 1 (furthest from the ammonia-solution tube), a mass of tufted leaves at the base}
five leaves higher up below any visible node, formed before the plants began to run up
stem (it was the same with the other plants, and with the leafy growth last year); higher
up five more leaves, four visible nodes, and a head; total height 30 inches; rachis
1} inch; three barren joints, and six with unripe seeds.

No. 2 (third from the tube), two dead shoots at the base, with several leaves each;
twelve leaves higher up on the main stem, lower ones 6 to 9 inches long, upper ones
shorter; four nodes visible; total height 28 inches; rachis 1} inch long, three barren
joints, and six with glumes and pales, but still green.

No. 3 (second from the tube), three stems: (a) 6 inches high; ten long narrow
leaves; stem dead. (4) 24 inches high; fourteen leaves below the first node, and three
higher up; two nodes visible; plant still growing and vigorous. (c) Height 31 inches;
twelve leaves below the first node, and three above it; swelled at the top with a head
not yet out.

No. 4 (nearest the tube), seven plants—five being small shoots 2 to 8 inches high, and
two main stems. As mentioned in respect to No. 1, and applicable pretty generally to
the Cereals with ammonia, a dense matted mass of leaves below the first node near the
base, 8, 12, and 15 inches long, with thick sheaths forming a dense coat at the base of
the stem. These plants are individually as follow:—(qa) 28 inches high; three nodes ;
rachis two inches long, with five barren joints, and seven with glumes and pales, and
seeds forming, green. (0) 35 inches high; four visible nodes ; rachis 2} inches long, with
five barren joints and seven with glumes and pales, and shrivelled seeds turning yellow.

The soil wet, soft, and loose, and not filling up the interstices among the flints.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 569,

The roots tolerably distributed throughout the whole pot, though not extending much
to the sides, but passing through all the holes at the bottom, and some at the sides, of
the pot, and forming a dense matted mass underneath it in the pan. Those of the
plants nearest to the watering and manuring tube have sent by far the most roots down-'
wards into the pan,—those furthest from it having their roots proportionally much more
confined in the soil near the base of the plant, where they are much matted, with diva-
ricate branches and short branchlets—these characters being more nearly those of the
Cereals grown without nitrogenous manure.

Preparation and analysis as described at pp. 543, 544.

No. 10.—Barley (1858); four seeds; prepared soil; with nitrogenous manure.
(See Plate XV. fig. 11.)

April 27.—Seeds set, and the pot placed over sulphuric acid, and covered with a glass
shade.

May 7.—The pot removed to its shade on the stand.

~ May 20.—Two plants up.

May 22.—A pipette-ful of the sulphate-of-ammonia solution (=0:004 gramme N.)
added to the soil.

_ May 29.—Two plants; 4 to 6 inches high; five leaves on each, the lowest dead, the
others green; improved since the addition of ammonia, more active growth and colour
deeper green. A pipette-ful of the phosphate-solution added.

June 7.—Second pipette-ful of the sulphate-of-ammonia solution added; also a
pipette-ful of the phosphate-solution.

June 19.—Two plants; 10 to 12 inches high, forming stem well; each plant seven
leaves; one stem has a small shoot forming at its base.

June 21.—Third pipette-ful of the sulphate-of-ammonia solution added.

June 26.—Fourth pipette-ful of the sulphate-of-ammonia solution added. Two plants;
16 to 18 inches high, healthy and vigorous; eight leaves each; also each a vigorously
growing shoot 4 to 5 inches long.

July 3.—Fifth pipette-ful of the sHihalot aaron solution added ; also a pipette-ful
of the phosphate-solution.

. July 12.—Sixth pipette-ful of the sulphate-of-ammonia solution added.

- July 14.—Seventh pipette-ful of the sulphate-of-ammonia solution BAe Two plants,
nae
_ No. 1. (a) Main stem, 26 inches high; lower leaves ripe or dead, and yellow, upper
ones green and growing; beard just appearing at the head. (6) Shoot, 18 inches high ;
three ripe or dead leaves, and three green.
~ No. 2. (a) Main stem, 28 inches high; lower leaves ripe or dead, four upper ones
green ; air-roots developing. (%) Shoot, 12 to 14 inches high; one dead, and four pit
leaves. (c) Shoot, 4 to 6 inches high; one dead, and three green leaves.

- July 19,—Kighth pipette-ful of the sulphate-of-ammonia solution added.

4n2

570 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

July 28.—Ninth pipette-ful of the sulphate-of-ammonia solution added.

July 29.—Only two of the seeds germinated; plants as follow :—

No. 1. (2) Main stem, out of the ground single, and then gives off (4) and (c); is
22 inches high; lower leaves dead, and lowest shows a fungous growth; six air-roots (two
still growing) from first joint or point of separation ; five nodes, each giving a leaf, only
the top one green; head bursting forth. (4) 28 inches high; five nodes, with leaves,
upper two only growing; stem slim below and thicker higher up; awns of head appear-
ing. (c) 5 inches high; two leaves; fresh and green.

No. 2. More vigorous than No. 1, and livelier colour; leaves the ground single; half
an inch up divides, and also gives off roots which go into the soil; three-quarters of an
inch higher a second shoot, and more roots given off; one reaches the soil, two growing
downwards, and several withered; lowest leaves dead and show fungous growth, parti-
cularly where they lie on the soil.

August 17.—TYenth pipette-ful of the ammonia-solution added (new solution
=0-00359N). Plants growing vigorously under the influence of the ammonia; nearly
at the top of the shade; several heads appearing.

August 24.—FEleventh pipette-ful of the ammonia-solution added.

September 7.—Twelfth pipette-ful of the ammonia-solution added.

October 5.—Plants ripening ; seven stems with heads; lower leaves of each dead or
ripe, and two or three upper ones of each green. Some new shoots appearing at the
base.

October 24.—Three heads green, the others ripe.

October 26.—Plants taken up :—

Only two seeds grew, and gave plants as follow:—

No. 1. Stem divided a little above the surface of the soil, giving plant (a), and an inch
higher up divides again, giving (4) and (c); below the first point of separation the stem
scarcely thicker than a pin, hard and solid. (a) 34 inches high; six visible nodes; stem
below the lowest very thin and hard, but larger, soft and succulent higher up; head
3 inches long, having sixteen joints, with glumes and pales, and awns 4 to 6 inches long;
two ripe plump seeds, and others shrivelled up. (2) 28 inches high; five nodes; below
the lowest stem hard, firm, dry, and almost solid, and but little thicker than a pin;
stem higher up larger, but still quite delicate; head 1} inch long, with three joints
barren, and seven with glumes, pales, and long awns, but no seed. (e¢) 30 inches high ;
five nodes; lower part of stem not quite so thick as (a) and (4); head ripe; rachis
24 inches long, with two joints barren, and thirteen with glumes, pales, and awns; also
some shrivelled seeds.

No. 2. Stem to 1} inch above the soil little thicker than a pin, quite solid, and firm ;
then a thick and bunchy node and six stems. Stem (a) 18 inches high to rachis; four
nodes; four leaves; crooked rachis 1} inch long, with three joints barren, and seven
with glumes, pales, and awns. (4) 21 inches high to head; rachis 23 inches long, with
three joints barren, and thirteen with glumes, pales, and long awns; four nodes; five

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 571

leaves. (c) green; 23 inches high, and still growing. (d), (e), and (f) about 25 inches
high to rachis; each with four or five nodes; rachis 1} inch long, with three or four
joints barren, and nine or ten with glumes, pales, and some green seeds.

The Root-development of these Barley plants was very extraordinary. Plant No. 1
has about ten roots coming from the first node or point of separation, extending deep
into the soil, and some eyen through the bottom of the pot; roots also come out from
the next joint above, on each of the separate stems, but these do not reach the soil.
Plant No. 2, from the first joint, whence spring the six stems, throws out more than a
dozen small roots, five of which reach the soil and ramify in it, some of the ramifications
going down into the pan. ‘The roots starting within the soil not so much matted near
the base of the stem as those of the Wheat; a good many go down and ramify amongst
the flints, or go through into the pan; they are finer, and not so much blunted and
divaricated as the Wheat roots. For illustration of the curious root-development of
the barley plant, see Plates XV. fig. 16.

Soil dry, loose, and porous.

Preparation and analysis as described at pp. 543, 544.

No. 11.—Oats (1858) ; four seeds; prepared soil; with nitrogenous manure.
(See Plate XV. fig. 12.)

April 27.—Seeds set, and pot placed over sulphuric acid, and covered with a glass
shade.

May 7.—The pot removed to its place on the stand.

May 20.—Three plants up; 4 to 43 inches high; two leaves each ; green and healthy.

May 22.—A pipette-ful of the sulphate-of-ammonia solution added (=0-004 grm. N.).

May 29.—Three plants; 5 to 7 inches high; four or five leaves each; two lowest
dead, three uppermost green and growing. These plants have increased the most of
any since the addition of ammonia. A pipette-ful of the phosphate-solution added.

June 7.—Second pipette-ful of the sulphate-of-ammonia solution added; also a
pipette-ful of the phosphate-solution.

June 19,—Three plants; 10 to 14 inches high; six leaves each; apparently somewhat
injured by hot sun the last few days.

June 21.—Third pipette-ful of the sulphate-of-ammonia solution added.

June 26.—Fourth pipette-ful of the sulphate-of-ammonia solution added. Three
plants, 12 to 14 inches high. No, 1, head developed and obviously seeds forming ; one
shoot 1 inch, and one 4 inches long from the base. No. 2, head forming; two shoots
from the base 4 to 5 inches long. No. 3, much like No. 2. Growth of main stems
apparently checked and that of shoots increased by some recent hot weather ; in all, six
shoots; green, healthy, and promising further growth.

July 3.—Fifth pipette-ful of the sulphate-of-ammonia solution, also a pipette-ful of
the phosphate-solution added,

July 12.—Sixth pipette-ful of the sulphate-of-ammonia solution added.

572 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

July 14.—Seventh pipette-ful of the sulphate-of-ammonia solution added. Plants as
follow :—

No. 1. Two stems; one ripe, with two or three seeds; six leaves, lowest dead ripe, and
five green. ‘The other stem 12 to 14 inches high; green; forming head.

No. 2. Three stems, from 12 to 15 inches high. One stem swelled at the top with a
head, but not maturing; checked early, apparently from want of available nitrogen,
after which the ammonia added developed the two shoots, whose stems are green, with
one dead and four green leaves, and heads forming.

No. 3. Two stems; one 8 to 10 inches high, dead or ripe; the other 14 to 15 inches
high, green and healthy.

July 30.—The plants taken up :—

The experiment stopped rather prematurely, the shade getting slightly cracked. The
plants had manifested three orders of growth, as follow :—

(1) The first growth, which was forming head when a fresh supply of ammonia gave
rise to shoots at the base. (2) The above shoots gave three headed stems: one with three
full and two imperfect seeds; one with two full and one imperfect seed; and one with
one full and two imperfect seeds. (3) New shoots from the base on the further addition
of ammonia; green and healthy at the close, but promising to go to seed.

The roots were very little more distributed than those of the Oats without nitrogenous
manure in No. 3 shade, and only extended about half the depth of the pot. The soil
was wet and soft.

Preparation and analysis as described at pp. 543, 544.

No. 12.—Beans (1858) ; three seeds; prepared soil; with nitrogenous manure.

April 27.—Seeds set, and the pot placed over sulphuric acid, and covered with a glass
shade.

May 20.—Pot removed to its shade on the stand. Three plants up; 23 inches high;
three leaves on each, colour dark green; healthy.

May 22.—A pipette-ful of the sulphuric-acid solution added.

May 29.—Three plants ; one dead, one much specked, the third improving. A pipette-
ful of the phosphate-solution added.

June 7.—A pipette-ful of the snilphRbcsok sackets solution added; also a pipette-
ful of the phosphate-solution.

~ June 19.—All apparently dying; leaves much specked with black.
June 21.—Plants all obviously past recovery; removed but not analysed.

No. 13.—Peas (1858); three seeds; prepared soil; with nitrogenous manure.
April 27. ea set, and the pot placed over sulphuric acid, and covered with a glass
shade. |
May 20.—Pot removed to its shade on the stand. Three plants up, growing exceed-
ingly well; 3, 23, and 1 inch high; three, two, and two leaves, respectively.

THE SOURCES OF THE NITROGEN OF VEGETATION, BIc. 573:

_ May 22.—A pipette-ful of the sulphuric acid solution added.

May 29.—One plant dead ; another sickly ; the third has given off shoots 3 to 4 inches
high, which appear healthy. A pipette-ful of the phosphate-solution added.

June 7.—A pipette-ful of the sulphate-of-ammonia solution (=0:004 gramme N.)
added; also a pipette-ful of the phosphate-solution.

June 19.—Two plants dead; the third has two green shoots, 3 and 6 inches high,
but delicate.

June 26.—The two shoots growing languidly ; seven leaves each; also some leaflets.

July 3.—A pipette-ful of the phosphate-solution added.

July 14.—Main shoot 12 to 15 inches high ; four lower leaves dead, four upper green ;
two shoots at the base dead, and one green and thriving.

July 29.—The two dead plants entirely prostrate, and near one a pale-green moss
formed on the surface of the soil. The third plant has three dead branches, and one
about 6 inches high with green leaves at the top.

August 17.—All the plants dead.

August 24.—Plants taken up, and submitted to analysis, although the growth so unsa-
tisfactory. Of course, of themselves, the results can have little weight in reference to
the question at issue.

No. 14.—Clover (1858) ; 226 seeds; prepared soil; with nitrogenous manure.

Two pots of Clover had been sown at the same time as the other plants, one to be
without, and the other with nitrogenous manure. ‘They came up well, but very soon
died; and on June 6 two more pots were sown in the same manner as before, excepting
that the ash was neutralized with sulphuric acid, and re-ignited before being mixed with
the soil; both also had a pipette-ful of the phosphate-solution, and the one that was to
have nitrogenous manure a pipette-ful of the ammonia-solution, at the time of sowing
the seed. ‘The one sown without the ammonia-solution failed so soon that the experi-
ment was abandoned early; the other (with the ammonia) forms the subject of the
following record.

June 6.—Seeds set as above, in soil with neutralized ash, and both phosphate and
sulphate-of-ammonia solution added*.

June 19.—A good deal up; actively and healthily growing.

June 21.—Second pipette-ful of the sulphate-of-ammonia solution added *.

June 26.—Third pipette-ful of the sulphate-of-ammonia solution added. Plants quite
green and healthy.

July 3.—Fourth pipette-ful of the sulphate-of-ammonia solution added; also a pipette-
ful of the phosphate-solution.

July 12.—Fifth pipette-ful of the sulphate-of-ammonia solution added.

July 14.—Sixth pipette-ful of the sulphate-of-ammonia solution added. Surface of

- * Tt is not quite certain that the ammonia-solution was added at this date; and in the Table of the
results (XIV. p. 531) it is assumed that it was not. <

574 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON

the soil covered with plants, growing well; 3 to 4 inches high, with two or three tri-
foliate leaves each.

July 19.—Seventh pipette-ful of the sulphate-of-ammonia solution added.

July 28.—Kighth pipette-ful of the sulphate-of-ammonia solution added.

July 29.—The plants growing, but not vigorously; some black and dead, and some
withering leaves; some petioles more than 4 inches long.

August 10.—Ninth pipette-ful of the sulphate-of-ammonia solution added.

August 17.—Tenth pipette-ful of the sulphate-of-ammonia solution added (new solu-
tion =0:00359 gramme N.). Green and growing well; twenty to twenty-five stems 4
to 6 inches high; a good many roots above ground,

September 7.—Eleventh pipette-ful of the sulphate-of-ammonia solution added. Large
strong roots visible; numerous leayes from the base; not much development of stem;
length of petioles 3 to 5 inches.

October 5.—Twelfth pipette-ful of the sulphate-of-ammonia solution added. Not
growing much, yet not dying; stems becoming bushy.

October 24.—Many of the lower petioles and leaves dead, and some a little mouldy ;
from the base of the dead petioles generally spring a number of green leaves, and petioles
2 to 4 inches long bearing green leaves, which look healthy, but almost stationary from
day to day.

October 26.—Plants taken up :—

Twenty-one plants; much as at last date.

Roots somewhat matted at the base, and throughout the surface of the soil; extending
2 to 3 inches through the soil, and some to the inner sides of the pot; none among the
flints, or in the pan under the pot.

Soil rather wet, loose, and porous.

Preparation and analysis as described at pp. 543, 544.

No. 15 (1858).— Wheat, Barley, Oats, Beans, Peas, and Clover, in a pot of Garden soil.

May 20.—Some of the plants just coming up.

May 29.—Wheat, Barley, and Oats, 6 to 8 inches high; Beans 4 to 6 inches high,
with some specks on the leaves; Clover up and growing. The condensed water yellowish,
and gives a yellowish-green deposit.

June 19.—The pot full of green herbage. Wheat, Barley, Oats, and Beans, all
healthy and growing well; Peas 3 to 4 inches high; Clover 2 to 3 inches, with three
leaflets.

June 26.—Wheat and Barley touch the top of the shade, and the plants crowded;
Clover 5 to 4 inches high.

July 14.—Shade full of growing matter. Wheat and Barley just heading.

August 2.—The Oat heading, with two grains; Wheat growing, but the ends of some
of the leaves dying. The two Beans quite black and dead. Several kinds of weed
come up; two in bloom.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 575

August 17.—Shade full of vegetable matter. Wheat, Barley, Oats, and weeds grow-
ing; but Leguminous plants dead.

September 7.—A good deal of growth yet.

October 5.—A good deal of grass and weeds growing. Cereals ripening.

October 24.—Shade full; experiment stopped. Wheat not quite ripe. Barley and
Oats dead ripe; Beans and Peas all dead; a little Clover still living; some grass, and
other weeds, green, and some seeded. ‘The whole soil filled with roots, many distributed
through the flints, and a large quantity growing in the pan under the pot.

No. 16.—Buckwheat (1858); forty-two seeds (1 gramme) ; prepared soil ;
with nitrogenous manure.

August 20.—Seed sown, and the pot placed over sulphuric acid, and covered with a
glass shade.

August 24.—Pot removed to its shade on the stand. Several plants up.

September 7.—A pipette-ful of the sulphate-of-ammonia solution added (=0:00359
gramme N.). Plants growing well.

October 5.—Second pipette-ful of the sulphate-of-ammonia solution added. Much
more vigorous than the Buckwheat without ammonia (No. 7); about twenty plants; 5
to 7 inches high ; four to six leaves on each.

October 24.—Third pipette-ful of the sulphate-of-ammonia solution added. Growing
well; 5 to 7 inches high; six plants in bloom. Comparing with No. 7, the influence
of ammonia here is very marked, as shown in size, vigour, and maturation.

November 22.—Plants taken up :—

Twenty-four plants; 4 to 7 inches high; five to seven leaves on each; six stems have
flowered ; bloom gone off and rudimentary seed formed ; would probably have grown
more but for frost.

Roots less in proportion to upward growth than with Buckwheat without ammonia ;
none deeper in the soil than 14 to 2 inches; slim, delicate, and but little distributed.

Soil loose and porous.

Preparation and analysis as described at pp. 543, 544.

No. 17 (1858).—Pants crown with Nirrogenous Manvrz IN M. G. Viuiz’s Case.

The same descriptions of pot, pan, soil, ash, &c., were used for these experiments as
for the others, as explained at page 565. Plants as under :—

W heat, four seeds; Barley, four seeds; Oats, four seeds; Beans, three seeds.

June 29.—Seeds set, and the pots placed over sulphuric acid, and covered with a glass
shade.

July 5.—Pots removed to M. VILuE’s Case.

July 14.—A pipette-ful of the sulphate-of-ammonia solution given to each pot
(=0-004 gramme N.). Wheat, four plants just appearing; Barley, three plants 14 inch

MDCCCLXI. 41

r

576 MR. J, B. LAWES, DR. GILBERT, AND DR. PUGH ON

high ; Oats, two plants just appearing; Beans, one plant 4 inches high, two others just
appearing.

July 19.—Second pipette-ful of the sulphate-of-ammonia solution to each pot.

July 28.—Third pipette-ful of the sulphate-of-ammonia solution to each pot of Cereals.

August 2.—Wheat, four plants; 7 inches high; extremities of some of the leaves
dying. Barley, three plants; two 9 inches, and one 7 inches high; two lower leaves of
each yellow, remainder green. Oats, two plants; 10 inches high; the lower leaf of
each dead, and the tips of some of the others turning yellow. Beans, two plants up;
one 8, and the other 6 inches high.

August 17.—Fourth pipette-ful of the sulphate-of-ammonia solution added (new solu-
tion, =0:00359 gramme N.). All the plants growing luxuriantly. Wheat, about 14
inches high; Barley and Oats, 8 to 12 inches high; Beans, 9 and 12 inches high.

September 7.—Fifth pipette-ful of the sulphate-of-ammonia solution added.

Wheat, four plants; (a) 14 inches high with ten leaves; (%) 13 inches high with nine
leaves; (c) 15 inches high with ten leaves; (d) 11 inches high with ten leaves.

Barley, three plants; (a) 23 inches high with eleven leaves; ()) 14 inches high with
ten leaves; (c) 25 inches high with eleven leaves.

Oats, two plants; (a) 26 inches high with seven leaves ; (4) 29 inches high, nine leaves.

Beans, two plants; main stems dead, but new shoots growing.

October 5.—Wheat, four healthy and vigorous plants; (a) 14 inches high; two
green and eight dead leaves; (4) 14 inches high; two green and seven dead leaves;
(c) 15 inches high; two green and eight dead leaves; (d) 14 inches high; three green
and eight dead leaves.

Barley, three plants; two healthy and vigorous, and one less so; (a) 24 inches high ;
three green and eight dead leaves; (6) 18 inches high; three green and seven dead
leaves; (c) 28 inches high; three green and eight dead leaves.

Oats, two healthy and vigorous plants, in ear; (a) 30 inches high; two green and
five dead leaves; (4) 30 inches high; two green and seven dead leaves.

Beans, two plants; (a) 9 inches high with three branches; (4) 14 inches high with
three branches.

October 24.—Wheat, four plants, erect and firm; much as on October 5, but larger;
no nodes visible ; but little tendency to form stem. Barley, much as on October 5. Oats,
much as on October 5. Beans, apparently ceased to grow.

Sixth pipette-ful of the sulphate-of-ammonia solution added. Wheat, four plants, 14
to 18 inches high; stems stout and erect, but without visible nodes; very leafy. Barley,
four plants, just coming to ear. Oats, two plants, main stems touching the top of the
Case ; (a) has a shoot 22 inches long springing from the first node 2 inches from the soil,
and coming into head ; (2) has three small shoots, one 3 inch and one 1 inch long, spring-
ing from the base, and one 3 inches long from the first node. Beans, slightly revived
since the last report.

THE SOURCES OF THE NITROGEN OF VEGETATION, ETC. 577

Notes on taking wp the Plants.

W heat taken up December 9.—The four plants all about the same size ; strong, healthy,
and vigorous ; ten to twelve long dead leaves each, 8,10, or 12 inches long, closely com-
pacted one above another at their base, and two or three green flourishing leaves each
at the top. Roots very thick and matted at the base, extending immediately around
in all directions, with short rootlets covered with divaricated branches, filling the upper
layers of soil; not many extend more than 24 inches down, very few go through the
bottom of the pot into the pan, and none ramify there. Soil loose, porous, and moist ;
and some water in the pan.

Barley taken up December 9.—Three plants; (a) 29 inches high, with a small shoot
(second growth) 1 inch long, from the base; fifteen leaves, two top ones green and
growing ; swelled at the top with a head forming; (0) 20 inches high; thirteen leaves,
upper ones green and growing; and indications of head forming; (c) much like (a) in
height, leaves, and shoot ; a short air-root from the first node. Roots the same character
in all; branched, considerably matted at the base, finely divided with numerous little
divaricate branchlets; only a few extend down into the pan, and they do not ramify
in it. Soil loose, open, porous, and moist; some water in the pan.

Oats taken up December 9.—Two plants:—(a) with two stems; one 32 inches high,
eleven imperfect seeds, and seven leaves; the other 26 inches high, coming from the
second node 2 inches up the main stem, with twelve seeds; six or eight air-roots 1 to 2
inches long, coming from the base node; a shoot an inch long from the lowest node, and
another lower down at the base. (4) A main stem with two long branched ones; main
stem 32 inches long, with five leaves and ten undeveloped seeds without solid nucleus ;
one branched stem, from the third node, 3 inches up the main stem, 14 inches long,
with three leaves, still green and growing; the other branch from the base of the main
stem 10 inches long, green and growing; some air-roots 1 to 2 inches long come from
the base of the largest branch, also several from the next node below, one or two of
which extend to the soil and ramify in it. There is also another small branch 2 to 3
inches long coming from the base of the plant and still green and growing. Roots
much alike in both; considerably matted at the base, little distributed, extending 3 or 4
inches in the upper parts of the soil, with many small divaricate branches; no roots in
the pan. Soil loose, porous, and moist; and some water in the pan.

Beans taken up December 9.—Two plants, with eight or ten leaves each; one 9 inches,
the other 14 inches high; both dead. The roots of both very much branched at the
base of the stem, but not extending deep into the pot, none going down to the flints. -

The Wheat, Barley, Oats, and Beans, prepared and analysed as described at
pp. 543, 544.

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