150 



the assimilation of free nitrogen by the earth, a fact which is in 

 conformit}^ with all observations made in extensive farminc; 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 drainage 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 ameliorating 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. 



Joulie arrives at very similar conclusions from experiments of the 

 same kind. The cultivation of buckwheat and of hay on a 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 

 twelve experiments, one only of which showed a loss of 0.013G 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 

 callable of directly fixing the nitrogen 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 difi'erent persons. Nothing is 

 wanting to them but the direct control to be obtained by a cliange in 

 the composition of the gases in which the plants grow. 



From this point of view the experiment is particularly difficult to 

 carry 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- 

 lous 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- 

 un'iphantly overcome all these difficulties. In a memt)ir published in 

 ISDO these clever experimentalists state that in the space of three 

 months three seeds of dwarf peas soAvn in a soil destitute of nitrogen, 

 but prepared in such a manner that the absorption of nitrogen 

 could easily take place, absorbed from 20 to 29 cubic centimeters of 

 nitrogen, weighing 32.5 milligrams and 30.5 milligrams, respectively. 

 This nitrogen, measured volumetrically, was found again (with all 

 the precision recpiisite in so delicate a research) partly in the soil. 



