384 BACTERIAL ORIGIN OF GUMS OF ARABIN GROUP, 



infection of the plant from without is thus indicated. In the 

 second place, every tree does not produce gum. This is, I think, 

 the strongest argument in favour of the mycological origin of the 

 substance. If gum acacia were a natural or even pathological 

 product of the plant itself, one would expect to find it more 

 uniforml3^ distributed than it is. It is not always even uniformly 

 distributed over the tree; some branches may be exuding gum 

 while others are not. The localised positions of gum-bearing 

 Acaciae are in accord with the theory that gum results from the 

 action of agents, such as bacteria, introduced by insects into the 

 tissues of the plant or by wind-borne dust, laden with bacteria, 

 lodging in a crack or wound. 



A recently gathered specimen of wattle gum, which I obtained 

 from Mr. J. H. Maiden, Government Botanist, showed, when 

 examined microscopically, a number of granules which might 

 have been the plasmolysed remains of bacteria. These were not 

 evident in older gums. 



Of interest also in this connection is the circumstance that 

 wattle gum has nutritive properties,* and that O'Sullivan found 

 a proteid in samples of Gedda gum. It is not at all improbable 

 that this proteid substance was the remains of bacterial cells. 



It would be useless to attempt the isolation and cultivation of 

 bacteria from fragments of dry gum, because any micro-organisms 

 that had been there would, during the process of drying, have 

 been killed plasmolytically. Fresh material must be investigated, 

 and to obtain this I applied to Mr. Maiden, who referred me to 

 Prof. Liversidge, in whose paddock at Mittagong he had seen a 

 specimen of Acacia penninervis bearing <a quantity of gum. Prof. 

 Liversidge sent me a gum-bearing branch, and this was investi- 

 gated. 



From the twigs small portions containing a drop of gum were 

 cut; from these the gum was removed and the part sterilised by 

 rapidly passing it through a bunsen flame. Smaller parts of these 



Maiden, Proc. Roy. Soc. N.S. Wales, xxxv., 171. 



