147 



first leaves, and this plant is soon as full i»f flowers and fruit as if 

 its entire fjrowtli had taken place in a soil of excellent (|uality. The 

 crop is then Aery f>;ood. It contains a large quantity of nitrog-en, 

 which evidently could only come to it from the atmosphere. 



This recrudescence of vegetation shows itself at a time when the 

 weight of the plant is eight or ten times that of the seed, and similar 

 contrasts are often observed in two stalks grown in the same pot, 

 which are, therefore, consequently in the same soil, under the same 

 conditions, the seeds being as similar as possible. 



In a Avord, the experiments of Yille teach us tAvo unforeseen and 

 equally remarkable facts. The first and most important is that a 

 leguminous plant can live and prosper in a soil entirely destitute of 

 all nitrogenous compounds, thus necessitating the direct assistance of 

 the atmosphere : the second is that all seeds of the same kind are 

 far from behaving in the same manner, whence it results that the 

 course of the experiment is eminently uncertain. 



AVith i^lants of the family of the Graminepe nothing similar takes 

 place. The results are absolutely invariable; the crop is zero if 

 the soil does not contain nitrogenous substances. It increases regu- 

 larly Avith the quantity of fertilizer, and each seed produces about 

 the same Aveight of dry material. 



The irregularity of the results givtm by the leguminosse under the 

 same conditions shoAvs that there could be in this case no question 

 as to the accidental gains of nitrogen, attributable to ammonia or 

 to atmospheric dusts, or to the Avater used in Avatering; the fact had 

 been disco A'ered, but its true cause had escaped the disco A'erer. 



(t. Yille, conA'inced of the correctness of the positi\"e results ob- 

 tained by him, Avas certainly right in concluding from them that cer- 

 tain kinds of plants attract carbonic-acid gas, but he Avas not master 

 of his experiment. Other obserA'ers also tried to repeat it after him, 

 but did not succeed. Boussingault, in particular, having placed his 

 plants in spaces that Avere too restricted to alloAv of the free develop- 

 ment of their roots, only obtained stunted plants Aveighing scarcely 

 four or fiAe times as nnich as the seed and containing no more nitro- 

 gen than the latter, because they had never attained the second stage 

 of their groAvth. 



In consecjuence Boussingault, Avho, hoAvcA'cr, had scAcral years be- 

 fore obtained results similar to those of Ville, thought himself justi- 

 fied in laying doAvn as a principle that A'egetables, no matter to Avhat 

 variety thev l)elong. are ahvays incapable of taking cA'en the smallest 

 quantity of nitrogen from the air. 



I shall not dAvell upon this discussion, Avhich has remained cele- 

 brated and Avhicli is very much to be regretted, inasnmch as the re- 

 sult of it Avas that by deterring those students Avho Avould have liked 

 to pursue the study of the question further its definitive solution Avas 

 retarded for thirty years. I only Avish here to confine myself to a 

 single point in it, Avhich is that the fixing of free nitroo^en by plants 

 Avas obserA-ed already in 1850, Avith all the characteristics of irregu- 

 larity belonging to it and as they have been again described in 

 recent physiological researches of German physiologists. 



I noAv come to the recent Avorlcs, and I shall commence by those of 

 Berthelot, in Avhich Ave shall l)e confronted by an entirely ncAV idea — 

 that of the interrelation of microscopic life and the phenomena of 

 vegetable nutrition. 



