266 



FIXATION OF FREE NITROGEN BY BACTERIA 



of F. NOBBE, E. SCHMID, L. HiLTNER, and E. HOTTER (II.), the nodule bacteria of 

 Elasaynus differ greatly from those of Leguminosce. 



These observations are also of importance to practical agriculture. Already, 

 for several years past, soils intended to be brought under cultivation (e.g. high 

 moorland soils) for the growth of nitrogen-collecting plants are previously 

 inoculated, i.e. strewn with a little earth from fields that have borne leguminous 

 plants for a long time, and are consequently rich in nodule-forming bacteria. 

 For this inoculation to have the desired result, it is necessary to use earth 

 containing the bacterial species most efficient for the kind of Leguminosce to be 

 afterwards grown. Practical experience on the importance of this consideration 

 is already available. Thus SALFELD (I.) has reported that a similar soil intended 

 for peas could not be rendered capable of yielding a crop unless strewn with a 

 little soil obtained from a good pea-field, soil from a lupin-field failing to produce 

 the desired efl'ect. A similar discovery was made by M. FLEISCHER (I.). This 

 treatment must, of course, be preceded by any improvement found necessary in 

 the chemical composition of the soil. Thus, for example, sour moorland must 

 previously be limed, in order to neutralise the acids preventing the development 

 of the nodule bacteria. Moreover, this operation must be performed with 

 discretion, an excessive addition of lime being avoided. Reference may be made 



on this point to a communication by TACKE, 

 IMMENDORF, HESSENLAND, SCHUTTE and 



'"\ ' / MlNSSEN (I.). 



" W 



195. The Bacteroids. 



The bacteria in question are often met 

 with in air and water, and very frequently 

 in the soil. NOBBE, SCHMID, HILTNER, and 

 HOTTER (I.) made several quantitative bac- 

 teriological investigations on this point. The 

 bacteria pass from the soil into the roots of 

 buch plants as will admit them. The first 

 successful, artificial production of nodules 

 by the aid of pure cultures was made by 

 A. PRAZMOWSKI (IV.). This worker, in 

 view of the absence of the sporogenic 

 faculty in these organisms, changed the 

 name of Bacillus radicicola, bestowed on 

 them by Beyerinck, into Bacterium radici- 

 cola. According to his observations, this 

 fission fungus penetrates the epidermal cells 

 of the root-hairs, and there develops to a 

 colony which then surrounds itself with a 

 . , tough membrane. From this original posi- 



Xuclear staining with i per cent, chromic acid ,1 i_ i. i j .cii j 



and methyiene blue ; k. the nucleus with tion there branches out a lustrous sac, filled 

 a vacuole; ; /. the with bacteria, which turns towards the bark 

 cells and branches out amongst them. As 

 a result of this advance towards the centre 



FIG. 62. Section through the bacteroidal 

 tissue of Latbyrus sylvestris. 



its nucieoius (lying i 



, f 

 central vacuole ; bact. the bacteroids. 



(4/ter Beyerinck.) of the root-hair, the cells thereof are incited 



to rapid increase and become densely 



crowded, in consequence of which they assume a polygonal outline, and constitute 



the bacteroidal tissue already mentioned (Fig. 62). The plasma of these cells, 



with its fungoid enclosures, has been termed mycoplasma by A. B. FRANK (VI.). 



Before tracing the career of the bacteria any further, a few explanatory 



