296 THE STRUCTURE OF RH1Z0BIUM LEGUMINOSARUM, 



much larger percentage of these irregular forms in suitable 

 (acidified) fluid media. This was the case with the acidophile 

 race obtained from the Blue Lupin (p. 287). When recently 

 isolated it produced an abundance of bacteroidal forms, but as 

 time went on the cells became more and more rod-shaped, until 

 at the time of making the fluid cultures few bacteroids were 

 obtained upon saccharose-bean-agar. The acidified fluid cultures, 

 when examined at the end of a fortnight, contained few rod- 

 shaped cells, the rest were well-defined bacteroids. 



Upon a maltose-citrate medium (p. 275) the cells imbedded in the 

 slime were of comparatively large size, measuring 0-9 : 3-4^., and 

 among the mass of rod-shaped organisms were many y and Y forms. 

 The cells were not readily coloured with the ordinary stains; in 

 the majority of cases they appeared in silhouette, the matrix or 

 slime around the cells being stained while the cell itself was 

 colourless. 



It was noted that the kind of nitrogenous nutrient had no 

 influence upon the formation of the branching forms, but this 

 could not be said with regard to the influence of salts, for some 

 acid radicles, e.g., citrate and phosphate, did seem to favour their 

 production. Much, however, depended upon the individual 

 bacterium. Differences occurred among the varieties of the races, 

 if such an expression may be used, even when these varieties 

 were isolated from the same nodule. This was very clearly 

 shown in the case of several cultures obtained from colonies 

 derived from a single nodule of the Blue Lupin. Some consisted 

 of short cells, others were long; some stained deeply, others 

 feebly; the irregular forms were few, with the exception of the 

 acidophile race, in which they were numerous. 



The percentage of salt (citrate) in the medium did not have 

 much effect upon the irregularity of the cells. In the absence of 

 saline matter the cells stained feebly; with 1 % they stained 

 deeply and irregularly. In experiments with acid and alkaline 

 media (p. 285) the reaction had little influence. 



For the production of a slime containing large stout cells with 

 many bacteroids, no medium appeared to be so suitable as one 



