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attained its full growth, entirely consumes the tubercles in order to 
assimilate them and thus form its seed. 
It is then, in short, by means of their roots that the leguminosee 
draw the nitrogen from the air, and this conclusion agrees with the 
well-known fact that a living leaf is incapable of modifying the 
volume of nitrogen into whic h it may be plunged, and that it is the 
root which in the first stage of vegetation always shows the greatest 
richness in nitrogen. 
It is the remains of these roots and the rupture of the tubercles 
that are carried on them which determine the enrichment of the 
soils of meadows, and the dispersion of the germs of the microbe 
that fixes the nitrogen. 
It has been objected to the conclusions of Hellriegel and Wil- 
farth that up to the present time it has been impossible to observe a 
fixing of nitrogen by the bacteroids alone independently of their 
symbiotic alliance with a leguminous plant. This is true, but it 
must be remembered that the obtaining of such proof is fraught with 
great experimental difficulties; the micro-organism, cultivated, we 
will suppose in a place where there is no nitrogen, will certainly take 
the nitrogen from the air, but not more than is necessary for the 
formation of its tissues; that is to say, an extremely minute ‘guanine? 
for the microbe itself weighs very little, and thus it happens nec- 
essarily that the phenomenon remains undetected by even the most 
delicate methods of analysis. 
In order that the absorption may be manifest it would be necessary 
that we should be able, as the Leguminose actually are, to take from 
the bacteroids their nitrogenous substance as fast as it is produced, 
or that it should be cultivated in such quantities that the dry weight 
should attain measurable quantity. Shall we ever discover the means 
of making this experiment? It is impossible to say at this moment, 
but what we can aflirm is that it 1s not correct to conclude, as certain 
authorities have done, that the bacteroids are incapable of fixing 
nitrogen gas when alone, basing their objections solely on the eround 
that up to the present moment “it has not been possible to prove such 
a fixation of nitrogen. 
Besides, atmospheric nitrogen is but a part of the complete nour- 
ishment of the Leguminose; since, in common with other species of 
plants, they can assimilate the nitrates and ammoniacal salts, 
although in a less degree. 
When a pea, a bean, or a lupin grows in a fertile soil it never shows 
that tendency to perish due to a “ famine of nitrogen,” which charac- 
terizes the same plants in a sterile soil; the plant’s vitality is great 
at the beginning of its growth and it is ‘for this reason that, in order 
to insure the success of his experiment, G. Ville advised that a 
small quantity of nitrogenous fertilizer be added to the mineral sub- 
stances that are given to the sand in which the plants were culti- 
vated; in this case, however, the tubercles are less abundant and the 
sum total of the nitrogen borrowed from the atmosphere is lower. 
If this bacteroidal action be not the only one capable of furnishing 
to leguminous plants the nitrogen necessary to them, there is evi- 
dently no occasion to draw.an absolute line of demarcation between 
these plants and others, which being less qualified to associate them- 
selves with the microbes (doubtless because the medium that these 
offer to them is less favorable to their development) derive, therefore, 
