t*ETHYBRiDGE — On the Rotting of Potato Tubers. 531 



summarized in 1908 by Pethybridge and Bowers (21). Since then further 

 work has been published by Longman (17) and by Manns (18). The cause 

 of the disease is generally regarded as being a species of Fusarium known as 

 F. solani Sacc, wliich is thought to be synonymous with F. oxysporum Schlect. ; 

 but, in view of the recent work of Appel and Wollenweber (2) on this genus, 

 it is not certain that this is really the species concerned, and it is possible that 

 the rot may be due to more than one species. A somewhat different form of 

 dry rot, termed an "external dry rot," has recently been described by 

 Jamieson and Wollenweber (15), and shown to be caused by a Fusarium, to 

 which the name F. trichothecioides Wolleuw. has been given. 



Frank (9) has credited the fungus Ht/pochnun solani Prill, and Del. (known 

 in his time as Bhisoctonia soi'ani Kiihu) with causing a wet rot in potato tubers 

 upon what to-day would be regarded as quite inconclusive evidence, seeing that 

 the inoculation experiments were not carried out with pure cultures of the 

 fungus. I think it somewhat doubtful whether this fungus, common as it is on 

 the tubers in the form of sclerotia, really causes any extensive rotting of them. 

 At any rate, I have endeavoured repeatedly to produce a rot with it, both 

 from material obtained naturally and from mycelium and sclerotia grown in 

 pure cultures, but so far witliout any success. When the fungus is intro- 

 duced into wounds in the tuber, it certainly grows in and around the wounded 

 cells, and may even invade a layer or two of the still healthy ones ; but a 

 newly formed layer of cork soon bars its further progress inwards. The result 

 is that a brownish felt, bearing sclerotia, is formed about the wound, doubtless 

 developed chiefly at the expense of the wounded cells, and no real rotting takes 

 place. I have kept inoculated tubers under observation under favourable 

 conditions for rotting for many months, with the result that they sprouted 

 quite normally, and the tubers showed no signs of rotting ; and I have come 

 to the conclusion that this fungus does noi, under such circumstances at least, 

 cause decay of the tuber. 



It must be conceded, however, that there are other workers who appear to 

 accept Frank's view that Hypochnus does cause a tuber rot. Thus McAlpine 

 (19) describes and illustrates a rot known as " brown-rust " in Tasmania, 

 which, he says, in some cases is due to this fungus. But while admitting that 

 this may be the case, it can scarcely be said that up to the present definite 

 and conclusive evidence in support of the contention has been brought 

 forward. 



which he bases the existence of various spore-bearing stages, supposedly belonging to one and the 

 same fungus, cannot possibly be accepted as satisfactory. Nectria solani Reinke and Bertliold was 

 described by these authors as being the perithecial stage of a Spicaria and not of a Fusarium. 

 Hypomyces solani being the perithecial stage of the latter. 



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