530 Scientific Proceedings, Royal Dnhlin Society. 



to either a very low temperature or one above their thermal death-point. Under 

 such circumstances it is easy to see that, when once dead, theirdecay can easily 

 be brought about by the very numerous species of saprophytic organisms, 

 abundant almost everywhere, provided that the latter are either capable of 

 entering through .the corky skin of the tuber or find an easier means of ingress 

 through the scar at the " heel " end or through some other wound in the skin. 

 As a rule, bowever, the rotting of potatoes is nowadays looked upon as 

 being the direct result of the attack of some parasitic organism ; and, before 

 proceeding to describe a new form of decay of this type, it will be well to 

 review very briefly the principal kinds of tuber destruction wliich have up to 

 the present been sliown on good evidence to be caused by definite organisms, 

 for purposes of comparison and contrast with the new form of rot. 



It is not proposed to deal here with the animal pests of potatoes, such as slugs, 

 wireworms, millipedes, mites, spring-tails, eelworms, ^c, more than to say, in 

 passing, that our knowledge as to the abilities of tlie members of some at least 

 of these groups to attack at first hand perfectly sound, healthy tubers is some- 

 what scanty, and that the direct destructive action of many of them which 

 can do so is probably of less consequence than the fact that the latter by 

 causing wounds in the skins of the tubers permit of the entrance of other 

 parasites, chiefly bacteria and fungi, which would otherwise fail to gain 

 admittance. 



A considerable number of bacteria, some of them more or less closely allied 

 to one another, have been described which are pathogenic to the potato tuber ; 

 and the literature dealing with the most important of these has been 

 summarized by Pethybridge and Murphy (22)^ in a recent publication, while, 

 to the list given there must now be added Schuster's Bacterium xanthochlorum 

 since described in a paper (25), in which references to further literature will 

 be found. 



The number oi fungi which have been proved to be the primary causes of 

 rotting in potato tubers is relatively small. The best known and most written 

 about is, of course, the " blight " iungns, Phi/tophthora infestans de Bary, 

 which, provided it is not associated in any large degree with other micro- 

 organisms, causes a characteristic dry rot. 



A considerable amount of literature has accumulated concerning what is 

 commonly known as the " Dry Eot "^ of tlie potato. The most important 

 papers dealing with this disease which had appeared up to that date were 



' The numbers in brackets refer to the bibliography at the end of this paper. 



^ Massee's so-called " "Winter Eot" (Diseases of Cultivated Plants and Trees. London, 1910, 

 p. 180), said to bedue to Nectria solani R. and B., is probably identical with this Dry Eot ; but this 

 author is certainly incorrect in his nomenclature of the organism causing it, and the evidence upon 



