202 Scientific Proceedings, Royal Dublin Society. 



Cause of the Mot. — We may at once anticipate the general conclusion at 

 which we have arrived as a result of our studies by stating here that the 

 fungus which we have found to be the cause of our common dry-rot is 

 Fusarium cceruleum (Lib.) Sacc, and that although it does directly cause the 

 decay of potato tubers, it does not produce hadromycosis (wilt) of the plant, 

 such as is produced by Verticillium alho-atrum, 1 and, according to some 

 authors, by certain species of Fusarium. Nor do we believe that it causes 

 a disease of the potato plant by attacking the roots. 



This species has been recognized on the Continent of Europe since the 

 beginning of the nineteenth century, but has not usually been regarded as a 

 definite parasite. Saccardo 3 records it as occurring in putrid tubers, and 

 Eabenhorst 3 on rotting potatoes. More recently Appel and Wollenweber 4 in 

 Germany state that it is a comparatively rare species on potato tubers ; and 

 these authors suggest that this may perhaps be accounted for by its slow 

 growth when compared with other species such as F. solani. This does not 

 necessarily conflict with our view that F. cairuleum is the species commonly 

 causing dry-rot, for the tubers examined by these authors were evidently not 

 merely those which had been destroyed by dry-rot, but must also have 

 included many killed by Fhytophthora infestans, parasitic bacteria, &c, on 

 which various saprophytic species of Fusarium subsequently flourish. 



Not nearly so much attention has been paid in America to this species as 

 to F. oxysporum, F. tricliothecioides, and others, although (as previously 

 mentioned), according to Sherbakoff, F. cceruleum is the commonest rot- 

 producing Fusarium in the United States, at any rate so far as the eastern 

 States are concerned. 



As a British fungus the species is recorded by Massee, 6 who gives an 

 extremely brief description of it, and states that it occurs " on rotten tubers 

 of potato," thus suggesting rather a saprophytic than a parasitic habit. In 

 British phytopathological literature the species is conspicuous by its absence 

 from mention. We cannot now be certain on the point, but a re-examination 

 of the fungus present on affected tubers, preserved both dry and in spirit 

 from the time of our 1908 paper, leads us to suspect strongly that what we 

 then called F. solani was in reality F. cairuleum. 



Eleven distinct cases of the disease have carefully been studied by us. 



1 Pethybridge, G. H. The Verticillium Disease of the Potato. Sci. Proc. Boy. 

 Dublin Soc. xv. (N.S.) No. 7. p. 63. March 1916. 



2 Saccardo. Syll. Fung. iv. 18S6, p. 705. 



3 Rabenhorst. Kryptog. Flora, I. 9, p. 574. 



4 Loc. cit. p. 84. 



6 Massee, G. British Fungus Flora, vol. iii. 1893, p. 481. 



