QUESTION OF THE SOURCES OF THE NITROGEN OF VEGETATION. 
53 
into nitric acid, and carried down into tlie subsoil, or into the drains. As to the gain 
bv the surface soil, he considers that part is due to the action of deep-rooted plants, 
in taking up the nitric acid accumulated in the lower layers, and leaving a nitrogenous 
residue near the surface ; a view in which we fully concur. As to gains not so to be 
accounted for, he considers it not yet settled whether they are due to the ammonia of 
the atmosphere, as supposed by M. Schlcesing, or to free nitrogen, as supposed by 
M. Berthelot. 
In conclusion it may be remarked that, if the losses in ordinary agriculture were in 
amount anything like those which M. Deherain’s figures show, even such large gains 
as are also indicated, would be far from sufficient to compensate them. It would 
indeed be necessary to seek for other sources of restoration, if our arable surface soils 
are not to lose their nitrogen much faster than we believe is the case in actual 
practice. That they do, however, slowly suffer reduction in their stock of nitrogen, 
when there is no restoration from without, there can we believe be no doubt. In 
other words, in actual practice, without such restoration from external sources, the 
losses are not fully compensated. 
3. The Experiments o/M. H. Joulie.* 
In this and subsequent sections, we have to consider evidence in regard to the 
fixation of free nitrogen, obtained, not in closed vessels, nor in the open field, but in 
vegetation experiments in which the soils and the plants were exposed to the free air, 
with known amounts of combined nitrogen supplied, and with more or less adequate 
precautions taken to exclude other sources than the free nitrogen of the atmosphere. 
M. Joulie’s experiments are, in point of date, the earliest of those we have to 
notice. 
M. JouLiE made two series of experiments on this subject. In the first he used a 
sandy-clay soil containing 0T04 per cent, of nitrogen, and in the second a sand 
containing only 0'0069 per cent, of nitrogen. In each series he used glass pots, with 
glass pans; in the first series he included 12 experiments, each in duplicate ; and in 
the second series 10 experunents, also each in duplicate. Pounded glass was put at 
the bottom of each pot, and in each case 1500 grams of the matrix was used. Pure 
distilled water was supplied to the pans, which also received the drainage; and above 
the level of the water there were slits in the pots, for the aeration of the soil and the 
roots. The pots were placed on a bench under a glass roof, and were protected from 
birds and rain by means of wire gauze ; the place of experi ment being a court-yard of 
the Municipal Hospital, Hue Faubourg St. Denis, Paris. The difierent experiments 
represented so many different conditions as to manuring, those of Series 1, being as 
under :— 
No. 1.—Without manure. 
* ‘Bulletin de la Societe des Agriculteiirs de France,’ No. 1, Janvier 1, 1886, pp. 19-29. 
