THE NODULE BACTERIA 265 



degree of acidity in the medium is represented by about 0.6 c.c. of normal acid 

 per 100 c.c. The plates coated with this nutrient medium are inoculated with 

 an infusion prepared by mixing a few c.c. of sterilised water with a small portion 

 of the contents of the bacteroidal tissue of a fresh, young nodule that has been 

 previously washed with water, then steeped a short time in alcohol, freed from 

 the latter by means of ether, and finally cut open with a sterilised knife. The 

 small quantity of inoculating liquid will be absorbed by the gelatin, leaving the 

 bacteria on the surface, where their growth progresses in the most favourable 

 manner. Here they develop to small mucinous colonies that do not liquefy the 

 gelatin. 



Two forms of cells will be immediately noticeable in preparations made from 

 such a culture. Beyerinck distinguishes them as rods and rovers. The former 

 have a breadth of i p. and a length of 4 to 5 p, and wander eagerly towards the 

 edge of the cover-glass, where fresh oxygen obtains access. As veritable dwarfs 

 in comparison with these are the rovers, which are only 0.9 p. long and o. 18 /* 

 broad, and therefore belong to the smallest of known micro-organisms. Even the 

 Chambeiiand filter cannot restrain them, and they escape through its pores. As 

 the name implies, they are endowed with motile power, which is frequently so 

 strong that individual rovers are able to escape from the parent colony, make 

 their way across the gelatin plate, and found a daughter colony at a distance. 

 The rod cells are not invariably of the ordinary cylindrical shape ; on the contrary, 

 variously bulged or lobed forms appear in larger or smaller number according to 

 circumstances, and a forked branching, resembling the Greek y, is very frequent. 

 This peculiarity, be it remarked en passant, is also shared by other bacterial 

 species, e.g. the Pasteuria ramosa already mentioned in an earlier paragraph. 

 Bacillus radicicola does not produce an enzyme capable of dissolving gelatin, 

 starch, or cellulose, or of inverting saccharose ; neither has spore formation been 

 detected, a circumstance harmonising with the fact that a temperature of 6o- 

 70 C. suffices to destroy this fission fungus. On the other hand, the organism 

 appears to support drought and frost without sustaining any injury. 



A few words must be devoted to the varieties exhibited by the nodule 

 bacteria. Hellriegel established (though without employing pure cultures) that 

 the nodule bacteria of peas cannot develop nodules on lupins and Seradella 

 (Ornithopus sativus). This observation, which was challenged by A. B. Frank, 

 was confirmed by NOBBE, working with pure cultures, in conjunction with 

 SCHMID, HILTNER, and HOTTER (I.). Whether the species should be divided 

 merely into races or varieties, as advocated by the observers just named; or 

 whether we should here speak of different species in the sense used by naturalists, 

 and consequently express them by different specific names, as was attempted, e.g. 

 by A. SCHNEIDER (I.), is a point of remote importance. BEYERINCK (XV.) has 

 also become a convert to this view, having been unsuccessful in inducing the 

 formation of nodules in Vicia Faba by means of bacterial cultures from those of 

 Ornithopus. On this point an interesting discovery was made by NOBBE, 

 HILTNER, and SCHMID (I.), according to whom the bacteria from any given species 

 of Leguminosce produce the most plentiful development of root-nodules in the 

 shortest time when applied to other plants of the same species, the potency 

 diminishing in the case of plants of merely allied species, and finally becoming nil 

 when a greater specific difference exists between the original plant and the one 

 inoculated. The various separate species (or varieties) of the nodule bacteria 

 can, to a certain extent, therefore replace one another. Thus, those of the pea 

 are also efficacious for all the examined species of the genera Vicia and Phaseolus, 

 but, on the other hand, without effect on Robinia, Ornithopus, red clover, 

 kidney vetch, and other clovers. Those of Robinia form nodules only on Phaseolus 

 and a few species of the genus Trifolium. Finally, according to the researches 



