156 



attained its full growth, entirely consumes the tubercles in order to 

 assimilate them and thus form its seed. 



It is then, in short, l)y means of their roots that the leguminoseix^ 

 draw the nitrogen from the air, and this conclusion agrees with the 

 well-known fact that a living leaf is incapable of modifying the 

 volume of nitrogen into which it may be plunged, and that it is the 

 root which in the first stage of vegetation always shows the greatest 

 richness in nitrogen. 



It is the remains of these roots and the rupture of the tubercles 

 that are carried on them which determine the enrichment of the 

 soils of meadows, and the dispersion of the germs of the microbe 

 that fixes the nitrogen. 



It has been objected to the conclusions of Hellriegel and AVil- 

 farth that up to the present time it has been impossible to observe a 

 fixing of nitrogen by the bacteroids alone independently of their 

 symbiotic alliance with a leguminous plant. This is true, but it 

 must be remembered that the obtaining of such proof is fraught with 

 great experimental difficulties; the micro-organism, cultivated, we 

 ivill suppose in a place where there is no nitrogen, Avill certainly take 

 the nitrogen from the air, but not more than is necessary for the 

 formation of its tissues; that is to say, an extremely minute quantity, 

 for the microbe itself weighs very little, and thus it happens nec- 

 essarily that the phenomenon remains undetected by even the most 

 delicate methods of analysis. 



In order that the al)sorption may be manifest it would be necessary 

 that we should be able, as the Leguminosa? actualh^ are, to take from 

 the bacteroids their nitrogenous substance as fast as it is produced, 

 or that it should be cultivated in such quantities that the dry Aveight 

 should attain measurable quantity. Shall we ever discover the means 

 of making this experiment ? It is impossible to say at this moment, 

 but what we can affirm is that it is not correct to conclude, as certain 

 authorities have done, that the bacteroids are incapable of fixing 

 nitrogen gas when alone, basing their objections solely on the ground 

 that up to the present moment it has not been ]:>ossible to prove such 

 a fixation of nitrogen. 



Besides, atmosplieric nitrogen is but a part of the comi^lete nour- 

 ishment of the Leguminosa^; since, in common with other species of 

 plants, they can assimilate the nitrates and ammoniacal salts, 

 although in a less degree. 



When a pea, a bean, or a lupin grows in a fertile soil it never shows 

 that tendency to perish due to a '' famine of nitrogen,"" which charac- 

 terizes the same plants in a sterile soil; the plant's Adtality is great 

 at the beginning of its growth and it is for this reason that, in order 

 to insure the success of his experiment, G. Ville advised that a 

 small quantity of niti'ogenous fertilizer be added to the mineral sub- 

 stances that are given to the sand in which the plants were culti- 

 vated; in this case, however, the tubercles are less abundant and the 

 sum total of the nitrogen borrowed from the atmos))here is lower. 



If this bacteroidal action be not the only one capalile of furnishing 

 to leguminous plants the nitrogen necessary to them, there is evi- 

 dently no occasion to draw an absolute line of demarcation between 

 these plants and others, which being less qualified to associate them- 

 selves with the microbes (doubtless because the medium that these 

 offer to them is less favorable to their development) derive, therefore, 



