462 FIXATION OF FREE NITROGEN 



Cultural Properties and Development of Nodule Bacteria. Prazmowski 

 recommends the following culture medium: An infusion is prepared 

 in hot water from leaves of leguminosse. After filtration and boiling, 

 gelatin, 7 per cent.; asparagin, J per cent.; saccharose, 0.5 per cent., 

 are added. The medium is standardized so that it contains 0.6 c.c. 

 normal acid to each 100 c.c The medium is kept in Petri dishes 

 which are inoculated in the following manner: A young nodule is 

 first washed in sterile water, afterward placed for a short time in 

 strong alcohol, and finally washed in ether, which is allowed to 

 evaporate. When dry the nodule is divided with a sterile knife and 

 the juice which escapes is spread with a platinum loop over the 

 surface of the medium, as it is there that the development of nodule 

 bacteria occurs best. Beyerinck described the organism so obtained 

 as showing two morphologic types. One is a rod 4 to 5 micra long, 

 1 micron thick, and the other a very small swarming rod, 0.9 micron 

 long and only 0.18 micron thick. The small bacilli can pass the 

 Chamberland filter and they wander away from their colonies on the 

 soft gelatin plates to form new colonies at a distance. The larger 

 rods are by no means regularly cylindrical, but some show branched 

 forms shaped like a Y. The Bacillus radicicola does not liquefy 

 gelatin, starch, or cellulose, and does not form spores. It is killed at 

 60 to 70 C., but is resistant to desiccation or freezing. 



Role of the Nodule Bacteria. The nodule bacteria of leguminosse 

 evidently differ, because those of one species often cannot form 

 nodules in another species, and, as a rule, can infect only species which 

 are very nearly allied. For instance, bacteria of the pea can form 

 nodules of the root of the bean, but not on the roots of different 

 species of clover; similarly, the bacteria of clover cannot infect and 

 enter into symbiotic community with the families Vicia (pea) and 

 Phaseolus (bean). Conn (Agricultural Bacteriology), discussing the 

 role of these microorganisms, states: "It is practically certain that 

 nearly all soils contain bacteria capable of living in symbiosis with 

 leguminous plants. Nearly all soils except extremely sandy soils, that 

 support little or no vegetation, will support leguminous plants and 

 develop tubercles on their roots. One can scarcely examine the 

 roots of legumes anywhere without finding tubercles, a fact which 

 shows that the bacteria in question are very widely distributed in 

 nature. But are the bacteria all of the same species? A very large 

 number of species of legumes with their tubercles can grow in most, if 

 not in all, soils. Are the bacteria that form tubercles on the clover the 

 same as those which form them upon the pea, or is there a different 

 species of bacteria for the different species of legume? It would 

 not seem probable that there could be in the soil a different variety 

 of bacteria for every variety of legume, but rather that one kind of 

 bacteria can grow in many legumes. But the facts are not quite so 

 simple as this. Not all species of legumes are capable of developing 

 root tubercles equally well in all soils. Some soils will luxuriantly 



