QUESTION OF THE SOURCES OF THE NITROGEN OF VEGETATION. 
95 
air, are such that results so obtained cannot of themselves be accepted without reserva¬ 
tion. But the fact that he found distinct gains in experiments in closed vessels, and 
that he obtained negative results with sterilised soils, is certainly in favour of the 
conclusion at which he arrived. 
M. JouLiE made numerous vegetation experiments in which the soils and the plants 
were, with certain precautions, exposed to the free air, and in which known amounts 
of combined nitrogen were supplied. He found very variable, but in some cases very 
large, gains of nitrogen. He considered that the variations of result were largely due 
to the varying conditions as to mineral-supply in the different experiments. 
M. JouLiE concluded that microbes probably play an important part in the fixation 
of nitrogen. He did not think that his results were favourable to the supposition 
that the plants themselves effected the fixation. For the present he limits himself 
to the establishment of the great fact of the fixation of the free nitrogen of the 
atmosphere, leaving to the future the exact explanation. 
It is to be observed that the large gains shown were chiefly with a polygonous 
plant, buckwheat, and not with plants of the leguminous family, which are reputed 
to be “ nitrogen collectors.” 
To show the practical importance of the fixation of free nitrogen, M. Joulie 
calculates what would be the gain per hectare according to some of his results. It 
may be confidently affirmed, however, that such gains as he so estimates, do not take 
place, either with or without vegetation, in ordinary soils, in ordinary practice. 
Dr. B. E. Dietzell made vegetation experiments, in which plants were watered 
with distilled water, the drainage was returned to the soils, and the pots and their 
contents were exposed to free air, but protected by a linen roof; a rich garden soil, 
containing 0’415 per cent, of nitrogen, was used, several different conditions as to 
manuring were adopted, and peas and clover were the subjects of experiment. Thus 
the plants were of the leguminous family ; but notwithstanding this, there was, in 
no case, a gain of nitrogen. In one there was neither gain nor loss, and in all the 
others there was a loss, in some cases amounting to about 15 per cent, of the total 
nitrogen involved. 
That there should be loss with a soil containing 0‘415 per cent, of nitrogen, that 
is about three times as much as most ordinary arable soils, is not at all surprising; and 
it is seen that, neither from the combined nitrogen of the atmosphere, or that due to 
other accidental sources, nor from free nitrogen, either directly or indirectly, did these 
reputed “nitrogen-collectors” gain nitrogen to compensate the losses from the rich 
soil. Indeed, Dr. Dietzell’s results are quite accordant with well established facts. 
Professor Frank also made vegetation experiments in free air. His soil was a 
humus-sand, containing only 0'0957 per cent, nitrogen; distilled water was used for 
watering, and the vessels were deep and narrow cylinders, without any arrangement 
at the bottom for drainage, or for aeration.* In three experiments without a plant, 
in one with two lupins, and in one with one lupin and incarnate clover together, 
* See foot-note at p. 61. 
