ir)7 



more benefit fi'Diii iiitro^jonous fertilizers. Between the Papilioiiacea^ 

 and the cereals, which occupy extreme positions in regard to the 

 capacity for fixing atmospheric nitrogen, there exist probably other 

 intermediate s})ecies capable of exercising the same function in every 

 degree. These latter nnist be less imi)r()ving to the soil than the Legu- 

 minosa'. but they must assuredly be less exhausting than wheat, 

 Indian corn, or beets, and it is impossible to exjilain 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 Cruciferte in particular aiv 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 

 knoAvn and Avhich i)erhaps act in the same way as the bacteroids 

 of the nodules. I shall not, however, insist upon facts which are 

 liable to discussion and Avhich require to be studied more minutely 

 and with all the care which has been bestowed upon the study of the 

 Leguminosea". 



I have now only one more ])oint to examine in regard to this ques- 

 tion, a 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 croj^s rapidly become less abundant, and 

 finally the soil is invaded by the (iraminea\ which raj)idly 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- 

 alile influence? Perhaps there is in this something very important, 

 which I can, hoAvever, 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 

 l)e that the bacterium of the nodules undergoes also a modification By 

 its prolonged contact with the roots of the Leguminosa* and that it 

 Avould 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. I 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 Leguminosa^ 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 



