Pethybridgk — The Verticillium Disease of the Potato. 85 



than one of those which are frequently found growing together on dead or 

 dying potato-stalks. 1 The principal literature on Curl (Krauselkrankheit), 

 from Kiihn's time onward, is dealt with by Reinke and Berthold in their 

 paper already referred to, so that it is not necessary to go further into the 

 matter here. It seems fairly clear that what is in the present paper called 

 the Verticillium disease was sometimes included in what was called Curl 

 (Krauselkrankheit) in the seventies of the nineteenth century. Whether, 

 however, the disease called Curl in the previous century applied solely to the 

 Verticillium disease is another question. On the whole, it seems likely that 

 it was only one of the diseases covered by this term. 



There is another form of "Curl" to which I called attention in 1912, 2 

 which cannot well be confounded with the Verticillium disease, and the cause 

 of which is quite unknown. Affected plants are small, and their foliage is 

 very much crumpled and curled. No fungus is present in the plants ; they 

 produce few and only small tubers, which reproduce the disease when planted. 

 In the cases studied by me the tubers produced in successive seasons became 

 smaller and smaller until, finally, they were not large enough to remain alive 

 until the spring, so that the race of abnormal plants died out completely. 

 This form of Curl has also been recognized in Germany and in America, 

 the term "curly dwarf" having recently been applied to it in the latter 

 country. 



Again, in England the term " leaf-curl " has recently been applied 3 to a 

 potato disease said to be due to Macrosporium solani (Cooke), but which still 

 lacks proper scientific study and investigation. Further, Vanha, 4 in 1910, 

 regarded a new fungus (Solanella rosea) as being responsible for a potato 

 disease, which he designated " curl " or " roll " disease (Krausel- oder Eoll- 

 krankheit), without, however, bringing forward really convincing evidence. 



Without going any further into the matter, it is quite clear that the term 

 "Curl" (or "Leaf-Curl") has been applied to several probably distinct diseases 

 of the potato, and it would therefore be well to refrain from the use of it in 

 future. 



In 1907 Appel 5 published a leaflet describing a disease of the potato which 



1 The solerotium, with appendages, described and figured by Hallier as a resting stage 

 of his R. tabifica, is, I have discovered, an early stage in the formation of its fructification 

 by a species of Colletotrichum, which I hope to describe elsewhere. 



2 "Jour. Dep. Agric. and Tech. Tnstr. Ireland," xii, 1912, p. 354. 



3 "Journal Board of Agric," vol. xii, 1905-1906, p. 476. lb., vol. xiii, 1907-1908, 

 p. 466. 



4 Vanha, J., "Die Krausel- oder Rollkrankheit der Kartoffel, ihre Ursache und 

 Bekampfung." Monatshefte f. Landwirtschaft, iii, 1910, p. 268. 



5 Appel, O., "Die Blattrollkrankheit der Kartoffel." Kais. Biol. Anst. f. Land- u. 

 Forstwirtschaft. Flugblatt 42, 1907. 



