442 IW. M. <'. Potter. On a Bacterial 



*' Ou a Bacterial Disease of the Turnip (Brassica net-pus)." By 

 M. C. POTTER, M.A., F.L.S., Professor of Botany in the 

 University of Durham College of Science, Newcastle-upon- 

 Tyne. Communicated by Sir M. FOSTER, Sec. R.S. Received 

 November 15, Read December 6, 1900. 



In the autumn, when the activity of the turnip plant is mainly 

 devoted to the storage of reserve material and the characteristic roots 

 are increasing in size, it is not uncommon in this neighbourhood to find 

 among the plants still growing in the fields some whose roots are quite 

 rotten and with a highly offensive and peculiar smell. 



The plants thus affected can be recognised by the drooping, yellow- 

 ish leaves, the older leaves being the first to show any indications of 

 disease. They gradually flag and droop to the ground, at the same 

 time becoming yellow and shrivelled in appearance. The leaves next 

 in age gradually exhibit the same signs of premature decay, and this 

 proceeds until finally the young leaves at the growing point succumb. 

 The time taken for the collapse of the leaves naturally varies with 

 different individuals, but it is usually about two weeks from the time of 

 the first infection. 



The roots of these plants when examined present a very character- 

 istic appearance. The decaying portion may be of a greyish-white or 

 dark-brown colour, and is quite soft to the touch ; the cell wall has lost 

 its natural firmness and the cells their turgidity, and with the escape of 

 the cell-sap the tissues have been reduced to a soft watery pidp. In 

 the particular disease now treated, the portion attacked remains of a 

 whitish colour, and I have therefore described it under the name 

 " White Rot," as my investigations have shown that this form of 

 rottenness is due to a specific organism producing this particular colour 

 when attacking a root. The brown and other discolorations found in 

 similarly diseased roots are probably due in part to this organism, 

 together with others, but I have not succeeded in cultivating the 

 " Brown Rot," and this awaits further investigation. 



The disease can be readily communicated to sound roots, it being 

 sufficient merely to make a slight incision and smear a small portion 

 of the rotten mass upon the injured surface for decay to be imme- 

 diately set up. In twenty-four hours the previously healthy cells 

 around the inoculated surface show the characteristic changes of form 

 and colour to a depth of about a quarter of an inch, indicating the 

 progression of the decay. Keeping the plant under observation, with- 

 out further injury, it is noted that the rind bordering on the wound 

 gradually becomes soft and assumes a lighter colour ; the discolora- 

 tion gradually extends ; the older leaves, too, droop and change colour ; 





