146 BACTERIA AND THE GUM OF HAKEA, 



ing a thickened mucilage. When boiled with 5 % sulphuric acid 

 for an hour, the bulk of the gum was hydrol3^sed to reducing 

 substances which readily j^elded osazone fractions. These were 

 found to consist of tarry impurity and galactosazone; no arabin- 

 osazone could be obtained. The remaining portion of the gum 

 hydrolysed to the same sugar. 



Already races of a bacterium which produced a galactan gum 

 and which gave the reactions for arabin had been separated from 

 the Sugar-Cane and from the Quince. The white race from the 

 Su^ar-Cane was different from this in its cultural characters, the 

 chief differences being in the nature of the colonies and the stab 

 in glucose-gelatine, its appearance on saccharose-potato-agar, the 

 absence of gas production in glucose media, the slow liquefaction 

 of the gelatine, and the larger size of the organism. As it does 

 not appear to have been hitherto described, I suggest the name 

 Bacillus pseudcu-abinus ii.^ in order that the bacteria which pro- 

 duce approximately similar gums may have approximately similar 

 names. 



The three bacteria, viz., Bac. levaniformans, Bad. metarahinum 

 and Bac. pseudarahinus ii., were the only active gum-formers 

 found in the branches that were examined. Since the natural 

 gum was different from those formed by the bacteria, there is the 

 probability that they did not directly produce the gum. At 

 present it cannot be said that the host-plant can modify the gum 

 once formed by these bacteria into another kind. We know that 

 it can induce the bacterium to produce a gum of another solu- 

 bility, and since it can do this it may be able to do a little more 

 and alter the nature of the gum. Of the bacteria, ^ac^ metara- 

 hinum produces a gum most nearly allied to the natural exudate. 

 The possibility that the natural gum might be pectin led me 

 to examine it in this light. Pectose* occurs in unripe fruits, etc., 

 and is insoluble in water and alcohol, but is converted into the 

 soluble modification known as pectin b}^ boiling with water 

 or dilute acids and by enzymes. The solution of pectin, like 



* Morley and Muir's edition of Watts' Dictionary of Chemistry; Eeynolds 

 Green's The Soluble Ferments. 



