154 



dried, and containing 1.733 grams of nitrogen. The total fixation 

 of nitrogen amonnted to 1.715 grams for the surface of the flowerpot, 

 or 274 kilograms per hectare. 



It is a remarkable fact that before the formation of the fruit the 

 nitrogen in the Leguminosa^ is, by preference, localized in their roots. 

 This fact is due to the great richness of the tubercles with which they 

 are covered. Breal found in the nodules of several plants, such as 

 kidney beans, peas, lupins, lentils, acacia, etc., as much as 7 part^ 

 of nitrogen to a hundred of dried material, i^ven when the fibers of 

 the roots never contained more than 2.5. 



Another fact, not less interesting, brought to light at the same time 

 by the experiments of Hellriegel and AVilfarth, is the difference 

 shown by arable soils in their capacity to initiate the appearance of 

 tubercles upon the roots of leguminous plants. Some of them are 

 ver}' efficient in this respect ; others are much less so. There are even 

 some soils which are more favorable to the production of tubercles 

 in certain species of plants than in others. This is a fact very diffi- 

 cult of explanation, for the solution of which further and bacteriolog- 

 ical researches will be necessary, because variations of this kind can 

 only be due to a difference in the microbe itself, the penetration of 

 which into the roots produces these nodules. 



In the experiments of Hellriegel and Wilfarth the sowings were 

 made with the washings from earth, containing, as we know, a mul- 

 titude of micro-organisms having different functions. Some of them, 

 it is true, Avere made with a liquid containing a little of the white 

 substance which comes from the nodules Avhen they are crushed, but 

 all i^recautions had ]iot been made to get rid of the germs which the 

 water itself might haA^e contained, or Avhich might have been brought 

 either by the young plant or by the atmospheric dusts. 



It was therefore necessary in order to be sure that the fixation of 

 the nitrogen was really due solely to the bacteria of the nodule, to 

 repeat the preceding experiments Avith all the precautions required 

 by microbic researches. 



This Avork of revision was carried out Avith scientific rigor by 

 Prazmoffski, in Cracow, with great success. 



The A'essels used for groAving the plants Avere provided A\'ith a 

 cover, which fitted tightly and had four holes pierced in it. One of 

 these holes, made in the center, permitted the young plant to pass 

 through it. The three others jillowed of Avatering and of the pas- 

 sage of a current of pure air. All these holes Avere closed with plugs 

 made of a sterile Avadding, which preA^ented the entrance of all germs 

 of exterior organisms. 



The so'il was formed of about 3,500 grams of siliceous sand, pre- 

 viously washed in boiling hydrochloric acid, then in Avater, and 

 finally heated red hot. Pure mineral fertilizers Avithout any nitro- 

 gen AAhatcA^er Avere then added to it. 



The Avhole mass was then sterilized bA' being heated for at least 

 tAvo hours from 140° to 150° C. 



In these A'essels peas which had been prcA^iously sterilized Avere 

 sown. To effect this they Avere first plunged into a solution of cor- 

 rosiA^e sublimate, then Avashed in alcohol, Avhich latter was finally 

 set on fire and burned upon the seed itself. 



Some of the A^essels receiA^ed also bacteroidal germs contained 

 in a nonnitrogenized bouillon culture liquid. 



