BY R. GREIG SMITH. 169 



The species of Sferculla appCcar to contain, normally, a mixture 

 of arabin and pararabin gums, and I have shown that two bacteria 

 are responsible for the production of these. In Halcea saligna 

 we have a case in which a gum, very similar to Linseed gum, is 

 found oozing from the plant; it differs from Linseed mucilage in 

 containing no cellulose. In the gummosis of the Sugar-cane the 

 gum can be seen only when the canes are cut transversely. 



The host-plant can alter the functional activity of the microbe 

 ao that a gum of a different chemical constitution is produced. 

 This was noted after Peach trees had been infected with the 

 arabin-former. Metarabin exuded, and in the tissues of the 

 plant were found transition forms between Bad. acacke and Bad. 

 metarahinum, which clearly indicated that the former was being 

 converted into the latter. Although Bad. acacke was in the 

 tissues of the plant, its product, arabin, was not in the exudate. It 

 was assumed that it had been there, but that it had been washed 

 away by rain. This assumption might have been wrong, for it is 

 just possible that the arabin had been altered directly into 

 metarabin. In Bad. macro zamke we have an organism that 

 produces the natural gum of Macrozamia and which formed the 

 same gum in the laboratory soon after its isolation. After a time, 

 however, the product altered, a gum with different chemical 

 reactions being formed. 



These instances show that the plant has, in some cases, a 

 tendency to alter the bacterial production of the gum. AVe 

 must believe that there is a reason for this. Either the alteration- 

 product is less noxious or it is more useful. I can hardly incline 

 to the former, because it is difficult to understand how a more 

 insoluble and, therefore, more viscous gum can be less harmful 

 than a limpid variety. It is more likel}^ that the plant tinds a 

 use for a limited quantity of the gum and that certain kinds are 

 adapted to certain plants. It is quite possible that the pectin 

 bodies may be in part formed from the gums that have been 

 prepared by bacteria. If the bacterium, which has gained entrj- 

 into the plant, produces a suitable gum, good and well, but if it 

 does not, the host modifies the functional activity. It may alter 



