146 



Lawes and Gilbert have thought to find an explanation of the 

 ameliorating influence of leguminous plants on the soil in the fact 

 that plants of that kind generally have very long roots and are there- 

 fore able to go much deeper in search of their nourishment than the 

 depth at which the roots of the Graminea^ are developed; the enrich- 

 ing of the earth would therefore be due to the organic debris that culti- 

 vation leaves there after the harvest, the nitrogen in Avhich had been 

 taken from the subsoil. The defect of this view is that the fertility 

 of the soil decreases rapidly as the depth increases, and in the 

 majority of cases the subsoil contains only such very insignificant 

 quantities of nitrogen that it is impossible to conceive "that any plant 

 could be nourished by it, particularly a leguminous plant which con- 

 tains in its tissues five or six times more nitrogen than does a 

 Gramineee. 



In a word, the most simple observations of j^ractical agriculture 

 show us that the amount of nitrogenous substances furnished by 

 nature would not suffice for the requirements of vegetation; it is 

 therefore indispensable that gaseous nitrogen should interpose di- 

 recth', and that, too, to an important extent, at least for the cultiva- 

 tion of leguminous plants. 



Mr. G. Ville proved this experimentally as early as 1849, and he 

 has not ceased repeating it since then, in spite of the systematic 

 opposition of most physiologists and agronomists. 



The primitive experiment of ^Ir. G. Yille has now become, by 

 recent labors in connection with it, an established fact. Allow^ me, 

 then, to describe it briefly, dwelling principally upon its results. 



In a sterile soil, containing at least 1 kilogram of calcined sand, 

 various leguminous plants, such as peas, beans, lupins, and others, 

 w^ere sown ; then were added some nutritive substances, either mineral 

 substances alone or a mixture of mineral fertilizers with a small 

 quantity of nitrate of soda, the object of which was to aid the young 

 plant to pass safely over the critical period of its growth, or, in 

 other words, the time when, having exhausted the alimentary re- 

 serves provided for it by its cotyledons, it must henceforth nourish 

 itself with substances entirely inorganic. 



The jDlants were watered with puvi} water free from annnonia; 

 every i^recaution Avas taken to assure the aeration of the soil; finally 

 the plants Avere kept in as pure an atmosphere as possible, either in 

 a glass cage, where from time to time carbonic-acid gas was intro- 

 duced, or, what is preferable in the open air, far from the laboratory, 

 and, in general, far from everything which could contribute to the 

 disengagement of ammonia. 



Under these conditions, and particularly when the soil received no 

 nitrogenous fertilizer, the plant remained puny at first, suffering from 

 wdiat the German physiologists have called "nitrogen famine." Some 

 plants even do not survive this })ainful stage of their existence, 

 but die without having sensibly increased their dry weight; others, 

 more vigorous, yield a mediocre crop; finally some, by the side of 

 other dying stalks, become suddenly very flourishing. Upon the first 

 stalk, which up to that time has been lank and without strength, a 

 new stalk seems in some way to graft itself — stronger, stiff, turges- 

 cent — which soon becomes covered with broad, well-developed leaves 

 of a green that are entirely different from the yellowish tint of the 



