594 "Corky Scab" of Potatoes. [nov., 



potato scab, at the time very prevalent in Norway, but, failing 

 to connect it with Berkeley's species, and considering it to be 

 an unknown form, described it under the name Spongospora 

 solani. Brunchorst added considerably to our knowledge of 

 the organism under consideration in clearly indicating that it 

 was in reality a member of the Myxogastres or Mycetozoa. 



Finally, Professor Johnson, of Dublin, discovered that " corky 

 scab " was rampant in the west of Ireland, and has made many 

 important observations respecting the cytology and general 

 life-history of Spongospora. 



From this brief account it will be seen that the organism 

 under consideration should now be known as Spongospora 

 scabies. 



Appearance of Diseased Potatoes. — " Scab " is the popular 

 term covering the general appearance of diseased tubers, but, 

 unfortunately the name "scab" is applied by the potato 

 grower to several diseases which differ very materially in origin. 

 One form of scab, very prevalent on potatoes grown in the 

 neighbourhood of towns, is induced by the physical action of 

 ashes on the growing tubers where night-soil mixed with ashes 

 is used as manure. A second form is due to the attacks of 

 eelworms on the surface of the tuber, while a third type is 

 caused by the millipede Julus pulchellus. American scab is 

 caused by Oospora scabies, Thaxt., a much reduced type of 

 fungal life. All the above forms of scab shew a close superficial 

 resemblance ; the surface of the tuber is more or less covered 

 with quite shallow wounds, round the margins of which a copious 

 formation of corky tissues is developed, and a rugged or scabbed 

 appearance is produced. The disease known as " Black Scab," 

 or more properly " Warty Disease " of potatoes, is entirely 

 distinct from the above kinds of scab, and does not resemble 

 them in appearance. 



The scab induced by Spongospora has received the appro- 

 priate name of " corky scab " on account of the considerable 

 development of wound-cork around the injured portions. 

 In the early stage ofthe disease small, dark-coloured, and slightly 

 raised patches appear on the surface of the tuber ; these, 

 however, are not as a rule uniformly scattered over the entire 

 surface, as in the forms of scab indicated above, but are more 

 or less localised. When the vegetative phase has been com- 



