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more benefit from nitrogenous fertilizers. Between the Papilonacex 
and the cereals, which occupy extreme positions in regard to the 
capacity for fixing atmospheric nitrogen, there exist probably other 
intermediate species capable of exercising the same function in every 
degree. These latter must be less improving to the soil than the Legu- 
minose, but they must assuredly be less exhausting than wheat 
Indian corn, or beets, and it is impossible to explain otherwise than 
by reasons of this kind the continued growth of forests and meadows 
which continue incessantly to furnish crops in soils which never 
cease to be much richer than our cereal soils, although they never 
receive any fertilizers. 
According to Ville, the Cruciferee in particular are capable of 
taking a part of their nitrogen directly from the air. On the other 
hand, we know that the roots of certain species of forest trees form a 
symbiosis with some kinds of mushrooms which are not yet well 
known and which perhaps act in the same way as the bacteroids 
of the nodules. I shall not, however, insist upon facts which are 
hhable to discussion and which require to be studied more minutely 
and with all the care which has been bestowed upon the study of the 
Leguminosee. 
I have now only one more point to examine in regard to this ques- 
tion, & point which, although still involved in obscurity, is neverthe- 
less very interesting. All planters are well aware of the fact that a 
leguminous plant can only be grown for a few years in the same soil. 
After being very flourishing for a short time a field of clover or of 
lucerne dwindles away, the crops rapidly become less abundant, and 
finally the soil is invaded by the Graminew, which rapidly transform 
the artificial meadow into a natural one, unless precautions have been 
taken, by clearing the land, to prevent the phenomenon. ‘To what can 
we attribute this spontaneous transformation? The microbe has had 
at its disposal all the elements necessary for its growth and its dis- 
semination. Why does it cease all of a sudden to exercise its favor- 
able influence? Perhaps there is in this something very important, 
which I can, however, only express in the form, of an hypothesis, but 
which, nevertheless, I think is worthy of having your attention called 
to it. Pasteur has shown us that certain inferior organisms change 
their nature, lose their noxiousness, or become more virulent if they 
are made to pass from one species of animal to another. May it not 
be that the bacterium of the nodules undergoes also a modification by 
its prolonged contact with the roots of the Leguminose and that it 
would be necessary for it, in order to resume its former functions, to 
pass to some other species of plants—in other words, to change its 
surroundings? Experience alone will solve this question. T will 
content myself here with putting it before you. 
Scientific researches sooner or later always find their practical 
applications; these that I have had the honor of bringing before 
you can not fail to render important services to agriculture. The 
“restoring ” -part played by the Leguminose is known to all agri- 
culturists: it has become an axiom of agriculture and forms the basis 
for the rotation of all crops; but after the experiments which we 
have just passed in review it assumes for us a strictly scientific char- 
acter which it did not possess before. The modus operandi of the 
process has been determined, and by a simple modification of the proc- 
esses of cultivation now in use, by assigning a still more extended 
