274 FORMATION OF SLIME OR GUM BY RHIZOBIUM LEGUMINOSARUM, 



in the more strongly acid stem. Furthermore, the location or the 

 sap of the localities of the plant in which the bacteria occur appear 

 to impart a temporary or permanent physiological character to 

 the microbe in making it unable to produce slime * 



The nutrition of the micro-organism. — Besides the examination 

 of the essential constituents of the slime, experiments were made 

 to determine the influence of various factors upon its production 

 and upon the relative physiological activity of the races. The 

 method of determination consisted in preparing media of varying 

 composition and in growing the racesf upon plates of tlie medium 

 contained in Petri-dishes. The volume of medium used in 

 each test was 20 c.c., and the slime that formed upon each of the 

 plates in seven days at 22° was carefully scraped off and weighed; 

 the plates were generally reinfected and any slime that formed 

 was scraped off upon the fourteenth day. The result was multi- 

 plied by five to give the quantity that would be obtained under 

 similar circumstances from 100 c.c. of medium, and the calcula- 

 tion was made to the nearest whole number. These numbers are 

 given in the tables. 



The vitality of the bacterium at the time of making the 

 experiment has so great an influence upon the result that one 

 experiment can only be compared with another in a general or 

 relative manner. It is for this reason that I have numbered the 

 experiments when more than one are, to economise space, grouped 

 into one table. Each experiment stands upon its own merits, for 

 the experimental conditions were the same. The variation of a 

 week or a month in making the experiment while making very 

 little relative difference in the results as a rule, made some 

 difference in the absolute weights of slime obtained. Even when 

 experiments are made at the same time, the experimental error 



* A somewhat similar alteration of function has been noted in the case of 

 Bact. acacice which in the Peach is altered to the metarabin-forming variety, 

 Bact. metarabinum (these Proceedings, 1904, 249). 



f The races were subcultivated upon saccharose-potato-agar or saccharose- 

 bean-agar, transfers being made twice a week, and the experimental plates 

 were infected with portions of these growths. 



