124 J5ACTEKIAL OHK^IN OF GUMS OF ARAIJIN GROUP, 



On cutting across a portion of the brancli at the end of Avhich 

 gum was adliering, minute clear droplets issued from the cut ends 

 of the large vessels of the wood. The droplets were, however, 

 found to be sterile, and doubtless consisted of sap. 



The transverse sections of the twigs and branches which had 

 been sterilised on the outside by flaming, were inserted into 

 nutrient glucose gelatine and incubated for from one to three 

 hours at oO^ The infected media were subsequently poured into 

 Petri-dishes and incubated at 22° for several days. Many 

 colonies of bacteria developed upon the plates, and among them 

 I identified Bad. acacice and Bac. levani/o7-mans, both of which, 

 as I have already shown, produce gum. The other bacteria could 

 not be induced to form gum by the methods which had been 

 successful in other cases, and it is probable that they were not 

 gum-producing bacteria. I always purify the bacteria from the 

 original colonies when they promise to be important, and in 

 purifying one or two races of Bact. acacice I found Bact. metara- 

 binum. 



In the presence of Bact. acacue, Bact. inetarahinum is not eas}^ 

 to separate. The deep colonies of both bacteria are very much 

 alike, and the sub-surface colonies of Bact. metarabinum, do not 

 break through to the surface to form a slime-drop colony like 

 Bact. acacice. It is only when the colon}' of Bact. ■/n.etarabvnum 

 is actually on the surface that it can be recognised with certainty, 

 and as there are comparative!}' few in original plate cultures, it 

 is not surprising that Bact. acacice can be readily isolated and 

 Bact. inetarabinuiii can be easily ignored. In the original separa- 

 tion of Bact. inctarabinum ivoiw Acacia peunitiervis, the bacterium 

 had been picked out of the plates as being a sub-surface colony 

 of Bact. acacue, and in the present instance its colonies had not 

 been observed upon the original plates. The occurrence of Bact. 

 tnetarablnum as an impurity in the original colonies of Bact. 

 acacue is a point to be remembered when the organism is not 

 found in the original plates. 



With regard to the presence of Bac. levaiiiforiaans in the plant, 

 it is probable that it is not responsible for the production of any 



