66 Scientific Proceedings, Royal Dublin Society. 



The view of the nature of the disease which has resulted from a study of 

 it during several seasons is that it consists primarily of a more or less prema- 

 ture death of the plant owing to a gradual process of desiccation, proceeding 

 from below upwards. It is to be regarded as a type of wilt-disease, although 

 actual wilting of the foliage— i.e. a condition of flaecidity, limpness, or loss 

 of turgor in the leaves while still green — is extremely rare in this country, 

 and has only been seen in cases where healthy plants have been artificially 

 inoculated through wounds with pure cultures of the fungus. 



Tn cases of severe attack the affected plants may attain the height of only 

 a few inches, and they may be killed off comparatively early and without 

 developing any curl or roll in the foliage. On the other hand, in cases of 

 very slight attack the plants may attain practically their normal size, and 

 may not begin to die off much before the usual time. Boiling or curling of 

 the foliage may here also be absent, and such cases of the disease are. easily 

 overlooked, particularly if the plants are at the same time attacked by blight 

 (Phytophthora infestans) or by the Botrytis disease. Of course, the greater 

 number of cases of the disease lie between these two extremes. 



In many cases after the death of the plants black streaks are noticeable 

 on the dead stalks. These are due to the production of the black form of 

 mycelium by the fungus and must not be confounded with the black, 

 adherent, flattened sclerotia of Botrytis so often seen on dead potato stalks. 



The only certain means of diagnosing the disease is by finding the 

 mycelium of Verticillium albo-atrum in the wood vessels of the plant or of 

 the tuber from which it is derived. Even the absence of the mycelium from 

 the wood vessels of the stem, root, &c, of a plant at a given moment is not 

 necessarily proof that such plant is not diseased, or at any rate that it will 

 not become so. For in many cases it has been found that the mycelium 

 passes from the parent tuber into the stalk rather slowly, and the foliage 

 may be just beginning to show typical symptoms of the disease before the 

 mycelium has reached the stem. The non-realization of this possibility has 

 doubtless been the cause of some at least of the contradictory statements 

 made with regard to this disease. 



Finally, it may be stated that no case of the disease has been met with 

 in which the affected plant has failed to bear some new tubers ; and since a 

 large proportion of these tubers contain the fungus within them, the disease 

 will spread to the next generation. The disease, therefore, is not extinguished 

 automatically in any given generation of affected plants, as has been supposed. 



III. Previous Investigation of the Disease. 

 As mentioned above, Beinke and Berthold in 1879 described the 

 disease due to Verticillium albo-atrum under the name of Curl-Disease 



