150 
the assimilation of free nitrogen by the earth, a fact which is in 
conformity with all observations made in extensive farming opera- 
tions. The distribution of this nitrogen in the plant shows that it 
enters through the roots, doubtless in consequence of microbic inter- 
vention. Finally, if we sum up the excess of nitrogen thus found in 
the crop and in the soil, together with the drain: age water, we should 
find, according to Berthelot, 300, 500, and even 700 kilograms per 
hectare, a part of which evidently remains in the ground as roots, if 
we are contented to gather only the portion of the crop which is above 
ground, as is generally done in practical agriculture. 
Thus it is that there results the progressive enriching of arable 
soils under the amehorating or improving action of leguminous 
plants; thus also results the “possibility of continuous cultivation of 
certain crops, such as meadow grass or forest trees, without fertilizers 
and without the earth becoming impoverished. 
Joule arrives at very similar conclusions from experiments of the 
same kind. The cultivation of buckwheat and of hay ona piece of land 
in the department of Dombes showed in two years a fixation of nitro- 
gen equal to more than 1,000 kilograms per hectare. The mean of 
tw ae experiments, one only of which showed a loss of 0.0136 gram 
per 1.5 kilograms of soil, showed a fixation of about 500 kilograms of 
nitrogen per hectare in a space of two years 
A little later Messrs. Gautier and Drouin also found, under the 
influence of the cultivation of common beans, an enrichment of their 
artificial soils which, as they estimated, corresponded to 185 kilo- 
grams per hectare for a single crop only. 
Finally Pagnoul, after having recognized that the soil alone is 
capable of directly fixing the nitr ogen of the air, found like the pre- 
ceding authorities that the enrichment of the soil took place to a con- 
siderable extent even with a simple crop of grass or clover. For the 
latter he found fixations amounting to 500 and 900 kilograms of 
nitrogen per hectare. 
We see that all these results are in absolute accord with each other, 
and, what is worthy of remark, they are of the same order of magni- 
tude in experiments made by several different persons. Nothing i Is 
wanting to them but the direet control to be obtained by a change i in 
the composition of the gases in which the plants grow. 
From this point of view the experiment is particularly difficult to 
‘arry out. The plants must be kept constantly in closed vases in a 
confined atmosphere, consequently in the presence of vapor of water 
at its maximum intensity, which seems to be an eminently unfavorable 
condition; besides, it is necessary to be able to measure the volumes 
of the gas contained in the apparatus, to analyze them with scrupu- 
leus exactitude, and, finally, to promote the chylophyllic nutrition by 
regular additions of carbonic acid without allowing the proportion of 
oxygen to vary too greatly. Schloesing, jr., and Laurent have tri- 
umphantly overcome all these difficulties. In a memoir published in 
1890 these clever experimentalists state that in the space of three 
months three seeds of dwarf peas sown in a soil destitute of nitrogen, 
but. prepared in such a manner that the absorption of nitrogen 
could easily take place, absorbed from 26 to 29 cubic centimeberss of 
nitrogen, weighing 32.5 milligrams and 36.5 milligrams, respectively. 
This nitrogen, measured volumetrically, was found again (with all 
the precision requisite in so delicate a research) partly in the soil, 
