QUESTION OF THE SOURCES OF THE NITROGEN OF VEGETATION. 
57 
On the other hand, the nse of organic matter, as farm-yard mannre, or dried hlood, 
much reduced the amount of fixation. The addition of calcium carbonate to the farm¬ 
yard manure increased the fixation, wliilst the same addition to the dried blood 
reduced it. 
When in the first series of experiments either phosphoric acid or potash was 
excluded from the mineral manure, there was a most remarkable decline in the 
amount of fixation, indicating, M. Joulie thinks, how necessary is a due balance of the 
mineral supplies for the full development of the action. 
In the second series, as in the first, the unfavourable influence of organic manures 
was obvious. 
M. Joulie concludes that his own results, like those of M. Berthelot, show that 
the fixation of nitrogen is due to a physiological action. Microbes play an important 
part; and his own experiments show that the action is developed in the absence of 
clay. His results were not very favourable to the supposition that the plants them¬ 
selves effected the fixation; but he considers that further comparative experiments, 
with and without vegetation, are necessary to settle the point. 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. 
In order to show the practical importance of the fixation of free nitrogen, M. Joulie 
takes for illustration the results of the experiment No. 5, in the first series, in which 
the largest amount of gain was indicated. In that experiment the complete mineral 
manure, with caustic lime in addition, was used, without any artificial supply of nitrogen. 
At the commencement the soil contained 1‘56 gram, and at the conclusion 2'042 grams 
of nitrogen, and the crops contained 0'3834 gram, showing a total gain, therefore, of 
0’8654 gram nitrogen. As the soil in the pots was 10 cm. deep, he calculates that 
this would correspond to 1144 kilograms of nitrogen fixed per hectare weighing 
2000 tonnes (= 1021 lbs. nitrog’en per acre). Or, reckoning only according to the 
relative superficies of the soil in the pots, and of a hectare, the gain of nitrogen would 
be 432 kilograms per hectare (=380 lbs. per acre). He further reckons, that the 
value of the nitrogen gained, at 1 franc 50 per kilogram as in manures would be 
1716 francs, or 650 francs per hectare (= 555 or 210 shillings per acre), according to 
the mode of calculation adopted. He admits, however, that it cannot be estimated so 
high, because the nitrogen fixed in the soil is in a form not at once assimilable 
by plants. 
In reference to the above results, M. Joulie says that our own at Bothamsted, and 
those of M. Deherain in France, obtained in field experiments, cannot be relied upon 
as the basis of conclusions on this subject; because the samples of soil taken at 
different times cannot exactly represent the mean composition of the soil, and because 
the layer of soil sampled may have lost combined nitrogen by drainage, or gained it 
from the subsoil. M. Joulie, on a former occasion, indicated in more detail his 
MDCCCLXXXIX.—B. 
I 
