155 



But in spite of all of thoso precautious it was not always possible to 

 prevent the })enetratiou of foreign organisms to the tubercles. In a 

 certain number, liowi'xcr, of tlie successful experiments in which the 

 bacteria alone remained in contact with (he roots (he results obtained 

 were identical with those obtained by IIellriei>el and Wilfarth. 

 There was a Hxation of nitr()<i-en in all the pots in whicii the hav- 

 teria were sowed, and in those only. 



Thus in a sterile soil, without microbes, a pea containin*^- 12 milli- 

 ^•rams of nitrooen ])roduced only l.KK) grams of dried crop, in whicli 

 18.2 milligrams of nitrogen were found, or about as much as was con- 

 tained in the seeds sown. Where microbes were present, on the (con- 

 trary, the dried crop weighed 3.544 grams and contained 82. (> milli- 

 grams of nitrogen. Therefore the bacteria had given to the plant 

 the faculty of taking from the air TO milligrams of nitrogen inde- 

 pendently of all other microbic intervention and under the same 

 exterior conditions. 



By using water in the place of sand Prazmoffski also obtained the 

 same results. Some peas grown in a nutrient solution without nitro- 

 gen and sterilized gave only 9 milligrams of nitrogen, whereas others 

 grown in a similar liquid but supplied with bacteria gave from 2(5 to 

 82 milligrams. 



These experiments then verify in the most complete manner the 

 views of Hellriegel and Wilfarth; the fixation of nitrogen by the 

 leguminoseiv is a consequence of their symbiotic union with an 

 infinitely small organism whose germs are profusely scattered abroad 

 and which enables these plants to grow sometimes with vigor without 

 any artificial inoculation in soils destitute of all nitrogenous food. 



It was these germs which "enabled (1. Ville to first observe the 

 fixation of atmospheric nitrogen by these same plants, and it was 

 their irregular dissemination which caused the inequality in his 

 experiments, and if Boussingault found it .inii)ossible to olitain the 

 same results it was simply l)ecanse he cultivated his plants under such 

 conditions that they could not acquire sufficient vitality to profit by 

 their union with these bacteroids. 



In effect at the beginning of vegetation in soils without nitrogen, 

 but into whicli microbes have been introduced, an interval of stop- 

 page of growth has been observed, so complete as to make us fear a 

 rapid decay of the plant, and this period of intermission always 

 coincides Avith the api)earance of the tubercles on the roots of the 

 plants. At this time the invading organisms derive their nourish- 

 ment from the juices of the young plant; they exhaust it, and if the 

 latter has not the strength to resist this invasion, which then con- 

 stitutes a sort of parasitism, if its roots are not able to develoj) freely, 

 or, again, if its leaves remaiji in a badly ventilated atmosphere, 

 always saturated with aqueous vapor, the plant Avill inevitably perish. 



If, on the contrary, it can resist, it will very soon gain the advan- 

 tage; it then takes from the bacteria the nitrogenous matter which 

 they contain and compels them to form more of it fi-om the nitrogen 

 which surroiuids them. Doubtless on its side the bacteriod pi-ofits 

 as much as the plant from its symbiosis; it is probable that it receives 

 from the latter hydrocarbons — sugars or others — in exchange for the 

 albuminoids which it gives to the plant, and thus it is (ha( this uuion 

 may exist until, finally, the moment arrives when the plant, having 



