384 
JOURNAL OF HORTICULTURE AND COTTAGE GARDENER. 
[ Octoter 81, 1889. 
At 'the end of the last century, or beginning of this, Ingenhousz, 
Sennebier, Woodhouse, and De Saussure became interested in the subject. 
Boussingault commenced his experiments in 1837 ; Ville, whose results 
■conflicted with those of Boussingault, in 1849 ; and, shortly after, this 
last named investigator started a new series of experiments which con¬ 
firmed his former conclusions that plants, under the conditions of the 
experiment, were not able to assimilate free nitrogen. 
In 1857 experiments on the assimilation of free nitrogen by plants 
were started at Rothamsted; and in 1861 was published in the 
Philosophical Transactions, the classical memoir of Lawes, Gilbert, and 
Pugh, on this subject. In this earlier paper a brief history and summary 
of the results of other experimenters is given, and then the recent 
results obtained at Rothamsted. The conclusions arrived at were 
identical with those of Boussingault, that there is no evidence that 
plants assimilate nitrogen. Still the authors allowed that there ware 
some difficulties with regard to the supply of nitrogen to leguminous 
plants, which assimilate from some source or another much more 
nitrogen than gramineous plants under similar conditions of Bupply of 
combined nitrogen. It was admitted that, “ if it be established that the 
processes of vegetation do not bring free nitrogen into combustion, it 
•still remains not very obvious to what actions a large proportion of the 
existing combined nitrogen may be attributed.” 
These views, that plants were unable to assimilate free nitrogen, were 
widely and generally held for many years, though there have always 
been some dissentients. In the meantime, however, the indefatigable 
investigators of Rothamsted have not been resting in the matter, but 
■have added much to our exact knowledge of the supplies of combined 
nitrogen to the soil from the air, on the amount and nature of the 
combined nitrogen in soils and in crops, on the processes of nitrification 
in soils, and the amount of nitrogen removed from soils in crops and in 
■drainage. During the last few years the main question as to the 
availability of atmospheric nitrogen to plants has taken a somewhat 
different aspect: it is now often suggested that though the higher plants 
are unable to directly take up free nitrogen, yet indirectly it is brought 
under contribution in some way ; the ways most generally favoured 
being either under the influence of electricity of low tension, or of 
microbes or some low forms of organisms ; and by such means it is 
thought that nitrogen is brought into a form in which it is useful to the 
higher plants. 
In Sir J. B. Lawes and Dr. Gilbert’s new memoir [“ On the Present 
Position of the Question of the Sources of the Nitrogen of Vegetation, 
with some New Results, and Preliminary Notice of New Lines of 
Investigation.” By Sir J. B. Lawes and Prof. J. H. Gilbert. Phil. 
Trans. 1889., clxxx. B. pp. 1-107.] they give a summary of some 
previously published Rothamsted results, chiefly relating to nitric acid 
in soils and subsoils ; also of the results of Cameron, S. W. Johnson, 
Hampe, Wagner, and Wolff, on the assimilation of nitrogen by plants, 
from more or less complex organic bodies like urea, uric acid, hippuric 
acid, and tyrosine. A number of new determinations of nitric acid in 
■soils and subsoils, and of total combined nitrogen in the surface soils of 
the Rothamsted experimental plots are given ; and also the results of 
numerous experiments with dilute solutions of organic acids on soils, to 
ascertain the action of such dilute acids, in some degree comparable to 
the acid sap of the roots of plants, on the organic nitrogenous matter of 
soils. In the second part of the memoir are summarised the recent 
results and conclusions of other workers relating to the fixation of free 
nitrogen. 
Probably the results of Berthelot, which have from time to time 
been published in the Comptes Rendus, have influenced the opinions and 
the course of inquiry in recent years more than any others. In 1876 
and 1877, Berthelot found that various organic compounds, under the 
influence of the silent electric discharge, even of low tension, were able 
to fix free nitrogen, and concluded that such fixation of nitrogen takes 
place in ordinary soils under normal conditions. In 1885 he published 
results showing the fixing of free nitrogen by certain soils under con¬ 
ditions which led him to believe that the action must be due to 
the influence of micro-organisms, and to such action M. Berthelot seems 
now inclined to impute most influence in the matter. Although the 
gains in nitrogen, expressed in per-centages, were very small, yet there 
was gain in all cases when the soils were exposed either in the open, or 
in a room, or in closed flasks, and no gain when the soils were sterilised. 
Unless there be some unrecognised source of error, such as might easily 
be imagined in the case of the freely exposed soils, one seems bound to 
accept Berthelot’s conclusions. Deiffi rain’s results at Grignon are next 
■discussed; they are chiefly on the gains or losses occurring on 
experimental field plots, and are perhaps not of such a nature as to 
materially assist one at the present stage of the inquiry. 
Joulie’s results, as given in the Bulletin de la Societe deg Agriculteun 
■de France in 1886 showed exceedingly large gains of nitrogen, which he 
is inclined to ascribe to the action of microbes ; here the gains of 
nitrogen were certainly more than take place in ordinary farm practice, 
and occurred with Buckwheat, which is not usually considered as a 
41 nitrogen collector.” 
Dietzell’s experiments are mentioned ; in all cases but one, in which 
there was a slight gain in nitrogen, the results are fully accordant with 
■established facts. B. Frank, who has recently written a paper on the 
whole aspect of the question, has published some experiments of his 
own. He concluded, as have others, that two opposite actions are at 
work in the soil—one setting nitrogen free, and the other bringing it 
into combination, the latter being favoured by vegetation—but that 
there is no decisive evidence to show how this combination is brought 
about; it does not necessarily follow that the plant itself effects the 
combination. Some of Frank’s experimental conditions, however, were 
considerably removed from those occurring in the ordinary course 
of farm practice. 
The very important and most interesting experiments of Hellriegel 
and Wilfarth follow. The first of these were described at the Berlin 
meeting of the Naturforscher-Versammlung, in 1886; subsequent 
experiments were described at the Wiesbaden meeting in 1887, and they 
were further given in a paper by Konig, published in Berlin in 1887 ; 
but the full text and details of their work were not published in time 
for Messrs. Lawes and Gilbert to refer to. A paper on these results 
appeared last November in Beilagelieft zu der Zeitsclirift des Vereint 
fur die Rubenzucher-Industrie, and the work of these investigators 
is described by M. Vesque in the January number of Annales 
Agronomiques. 
The experiments date from 1883 onwards, and were on cereals, 
Buckwheat, Rape, and various leguminous plants. The plants were 
grown in pots in washed siliceous sand, to which the necessary cinereal 
constituents were added. In this all the plants grew normally until 
the nitrogen in the seed was used up ; then the plants not belonging to 
the Leguminoste ceased growing until supplied with some combined 
nitrogen, nitrate of soda was used, when growth was proceeded with 
almost exactly in proportion to the amount of nitrogen supplied. With 
the Leguminosoa the results were more eccentric ; sometimes the plants 
died of nitrogen-hunger ; sometimes after a time of such hunger they 
recovered and produced abundant growth. To the sterile soil with the 
young plants there was added in a large number of cases a small 
quantity of an extract of a garden soil; the extract used contained less 
than one milligramme of nitrogen ; the Oats, Rape, and Buckwheat re¬ 
mained undeveloped, but the leguminous plants soon became deep green 
and grew vigorously. If the soil extract were previously sterilised by 
heat, it produced no effect. Moreover the soil used in the preparation 
of the extract was of importance ; with Peas any soil extract answered, 
but not so with Lupins and Sainfoin. With these plants, to render 
success certain it was found necessary to use an extract of a soil which 
had previously grown the same plants. Some experiments were also 
made in large sealed flasks, to which carbon dioxide was admitted at 
intervals ; in these the results were practically the same as in free air, 
showing that it was not the combined nitrogen of the air which was 
absorbed. 
It was also found that whilst on the leguminous plants which deve¬ 
loped well, either with or without the addition of soil extract, the 
characteristic tubercules of papilionaceous plants were well marked, on 
those which did not develop in the sterile soil, and also on plants grown 
in sterilised soil to which nitrate had been added, and which plants 
developed at the expense of the added nitrogen, but did not assimilate 
free nitrogen, there were no tubercules. Hence there is obviously some 
connection between the production of the tubercules and the assimila¬ 
tion of the free nitrogen. In aU cases where free nitrogen is pre¬ 
sumably assimilated by the plant, the soil is also enriched in nitrogen, 
the more so when the plant growth is more vigorous, and this excess of 
nitrogen in the soil is almost entirely in organic combination. 
The general conclusions are that leguminous plants, though they are 
able to make use of combined nitrogen in similar forms to those the 
graminaceous plants utilise, yet differ from this latter order of plants in 
being able to use some other form of nitrogen, not that existing in the 
soil. This second source of nitrogen must be the free nitrogen of the 
air, which the Leguminosae utilise through the agency of certain micro¬ 
organisms which are in symbiosis with them, and exist in the tubercules 
of the roots of this order of plants. 
The results obtained by Von Wolff at Hohenheim from 1883 onwards 
are mentioned. Wolff is not inclined to admit that plants assimilate 
free nitrogen, but thinks that the only remaining hypothesis is that 
certain plants can appropriate the combined nitrogen of the air, either 
directly through their leaves or more probably after absorption by the 
soil. A porous soil probably absorbs far more nitrogenous compounds 
from the air than an equal superficial area of dilute acid, as used in 
experiments by Schloesing, Kellner, and Muller. He admits, however, 
that it is difficult to see why the grasses are unable to benefit by this 
equally with the legumes. 
W. 0. Atwater has published three papers on various aspects of the 
subject in the American Chemical Journal. In these papers he gives 
results of his own experiments and also discusses those of others. He 
concludes that in many of his experiments with Peas, when the growth 
was normal, half or more of the total nitrogen of the developed plants 
was obtained from the air. In what way the nitrogen was acquired the 
experiments do not show, but Atwater inclines to the idea that the 
plants themselves directly acquired the atmospheric nitrogen. The 
conclusion of this second part of the memoir gives some recent experi¬ 
ments and opinions of Boussingault on the subject. He remained 
strongly of the opinion that plants were unable to assimilate free 
nitrogen ; although, as is here pointed out, some of his experiments in 
1858 and 1859 with Lupins might be considered as leading to such a 
conclusion. 
The third part of the memoir gives a summary and general consider¬ 
ation and conclusions. Regarding the evidence relating to other sources 
than free nitrogen, Lawes and Gilbert have shown that the amount of 
nitric acid remaining in a soil is much less after the growth of a crop 
than under corresponding conditions without a crop. Also that nitrifica¬ 
tion in soils is more active where leguminous crops are grown than 
where gramineous plants only are present; and that deep-rooted 
