189 



nutrient liquids, but with a, solid mediinu, the lesults are quite the 

 same: fixation of uitrogeu does not take place then either. Stress must be 

 laid on the latter fact as it seems im[)0ssible to tix free nitrogen 

 by the Papilionaceae when cultivated in liquid media even under 

 the l)esl circumstances aud whether tubercles are pi-odnced or 

 not. So it seeuis probable that for this j)rocess a direct contact with 

 the air is necessary, which cannot be i-ealised iu the li(piid culture 

 media, but very well in solid ones. 



Further it must l)e observed that the plate cullui*es of. some of 

 the nodule organisms,') for example the forms from /^/.sv^/??, Vicia,Rnd 

 Tflfoliniu, on gluco8e-agar-potassiumphos[)hate |)Iates, in absence of 

 purposely added nitrogen compounds, at superficial view make the 

 impression of being quite able to develop, but here too, it is 

 only the formation of much wall substance, as already described 

 above, and not of nitrogen-rich protoj)lasm, which explains the 

 voluminosity of the colonies.^) With other slime-producing bacteria, 

 as B. radiohacter and Aerobacter viscosian, of which it is quite 

 certain that they cannot live on the atmospheric nitrogen, extensive 

 colonies may likewise be grown on the said nitrogen-poor medium 

 with tit carbon food. By a better nitrogen nutrition such colonies 

 may even be greatly reduced iu volume, the wall substance then 

 serving as food under a strong increase of the bacterial protoplasm, 

 which gives rise to vei-y interesting experiments. It is only when 

 being ac(piainted with' these facts by personal observation that we 

 can understand how in the literature so many statements can occur 

 on the nitrogen fixation by the nodule bacteria, which does not 

 take place. 



Within the nodtdes the atmospheric nitrogen is neither fixed. 



The preceding gives rise to the question, whether the proto|)lasm 

 of the host [)laut might be the catalyst that enables (he invading 

 bacteria, iu their bacteroidal state, to fix the free nitrogen. However 

 improbable this hypothesis may appear, being in contradiction with 

 the laws of heredity, still it deserves attention because the i-ate of 



') The wonderful "experiments" of Maze (Annales de rinstilut Pasteur T. 11, 

 pag. 44, 1897, T. 12, pag. 1 and pag, 128, 1898), who asserts that on broth 

 gelatin plates at the same time ammoniumcarbonate is produced and fixation of free 

 nitrogen by B. radicicola takes place, need not be considered, although they are 

 taken up uncrilisised in the handbooks of Pianlphysiology. 



2) Likewise for the ordinary saprophytic bacteria the want of nitrogen compounds 

 varies very much : the large-celled Bacillus megatherium requires very little, the 

 small celled Bacterium fliiorescens very much. 



