A DISEASE IN TURNIPS CAUSED BY BACTERIA 35 



rods were formed in a day or two, which liquified the gelatine, 

 Unfortunately, there was no opportunity at the time of infecting 

 healthy swedes from these colonies, and of following the entire life 

 history of the bacteria. 



As a careful field examination seemed desirable, a visit was 



made to the injured crops in Yorkshire. The disease had advanced 



very rapidly ; fields of swedes that appeared healthy and thriving a 



(V fortnight previously were now completely 



? ^ ^ ^ ^ blighted. In the worst field, twenty-five 



// J^ acres in extent, not one turnip in five 



6^ seemed to have escaped. Yellow turnips 



^ '^^ ^ had suffered very little, though here and 



\\, ^0 0^ here a few plants growing on the head 



ff ^ rows of the fields containing diseased 



f /J swedes were attacked; cabbages growing 



'^^ near were also diseased, but a strip of 



X 2000. kohl-rabi right through the centre of a 



Bacteria which cause the dis- severely diseased crop was quite healthy. 



ease in the turnip. Mag- The kohl-rabi appears so far to be im- 



nified 2000 diameters. mune, and cabbages and yellow turnips 



are probably safe when not in contact with a diseased crop. The 



mangolds growing in the same field were not in the least attacked. 



In all cases the bacteria had lodged in the central bud, by destroying 



the tissues of the turnip below, so that the young leaves were cut 



off from their connection with the root, and they speedily withered 



and died. Where circumstances favoured the development of the 



bacteria, they increased rapidly, and the whole interior of the root 



from the crown downwards was soon destroyed. 



For the information of farmers, who in some districts were 

 alarmed at the serious injury to their crops, a letter was pubHshed 

 four months ago in the Times and other daily papers, and in the 

 Agricultural Gazette, giving a general account of the nature of the 

 disease, and suggesting steps to be taken to prevent its spreading. 



The disease worked great havoc in Yorkshire, and the same 

 injury was reported from two localities at a distance from each 

 other in Dumfriesshire. At a later period the progress of the 

 disease was to a large extent arrested. This no doubt arose from 

 the destruction of so many leaves, which left the rows somewhat 

 bare. Sunlight and air gained free access to the bulbs, and the 

 bacteria were dried up or destroyed. 



Many investigators in recent years have experimented on the 

 influence of sunlight on bacteria, and have proved that in most 

 cases they develop only in darkness. In 1877 and 1878 Downes 

 and Blunt found that, while their growth was retarded by the 

 influence of diffused white daylight, it was completely stopped by 

 sunshine. Another observer found that the destruction of germs 

 was more rapid and complete when there was also a free admittance 

 of air, though one of the most recent workers in this field. Professor 

 Marshall Ward, has shown that the sun's rays alone are sufficient 

 to kill them. He confirmed this view by exposing to the light 

 plate cultures of the spores of the anthrax bacteria covered with 



D 2 



