Some Saprophytic Fungi of Potatoes. G. H. Pethybridge. 105 



This fungus is found quite frequently on the surfaces of decayed 

 potato tubers in its well-known red conidial stage. It was 

 grown in pure culture for a period of fifteen months on various 

 nutrient media in the hope that some other form of fructifica- 

 tion might develop in one or other of them. This, however; ■ 

 did not occur. 



In July 1915 a number of old, diseased "seed" potatoes 

 that had been thrown into a wet ditch in the spring were 

 examined, more or less as a matter of curiosity. On the surfaces 

 of several of these tubers a number of perithecia were found. 

 A few of the latter were almost black ; and microscopical exami- 

 nation showed that they probably belonged to some species 

 of Gibberella. Most of the perithecia, however, were dark red 

 in colour, somewhat similar to those of Hypomyces Solani R. et 

 B. Since, however, a stroma was present it was evident that 

 they belonged not to the genus Hypomyces, but to Nectria. 

 Comparison with type material of A^. Solani R. et B. showed that 

 they were certainly not that species*. 



Closely associated with the red perithecia was a copious 

 development of the conidial stage of V. cinnaharinum, so close, 

 in fact, that in some cases conidiophores of this fungus were 

 present on the stroma, and even on the surfaces of the peri- 

 thecia themselves. The question arose, therefore, as to whether 

 this was a case of mere association, or whether the perithecia 

 actually belonged to V. cinnaharinum. Many of the perithecia 

 were still unripe, but in others ripe ascospores were present, 

 and trials made in hanging-drops showed that the spores were 

 viable. 



Careful and continuous microscopic observations w^ere made 

 in five separate instances on the development of isolated indi- 

 vidual ascospores in film cultures on the undersides of cover- 

 glasses, this being a more advantageous method of study than 

 the hanging-drop. In each case the spore germinated and 

 produced mycelium, which soon gave rise to conidiophores and 

 conidia exactly similar to those of V. cinnaharinum, the growth 

 from the original ascospore to the development of conidio- 

 phores and conidia being traced in unbroken sequence. 



In another case the course of development from ascospore 

 to conidia-production was followed under the microscope with 

 a culture on a thin film of nutrient medium in a Petri dish. 

 This is illustrated in Fig. 3, Plate III. The two-celled ascospore 



* N . Solani does not appear to be a common species. I have never come 

 across it and there is no reliable record of its occurrence in the British Isles. 

 For years, however, in EngUsh phytopathological literature this fungus was 

 credited, quite erroneously, with being the cause of the dry-rot of the potato 

 tuber. 



