PYRENOCHAETA 419 



very obvious on fresh tubers, but after storing, when a certain 

 amount of dessication has taken place and the surface has 

 become rugged, minute black points micro-sclerotia become 

 visible to the naked eye. These black points are the essential 

 characteristics of the disease. In certain kinds of potatoes, 

 where the skin constantly and normally peels off in small 

 flakes, the black points are removed with the flakes, and it is 

 difficult to observe the disease unless microscopic sections of 

 the skin are examined. The root and stem are also attacked, 

 and eventually become covered with black points. If an 

 infected tuber is used as ' seed,' the mycelium often passes 

 into the young tubers, which are killed. The young tubers 

 may also become infected by sclerotia in the soil, if a diseased 

 crop has been grown previously. 



The general aspect of the disease, with the minute black 

 sclerotia nestling in the epidermal cells, recalls to mind the 

 scab caused by Spondylodadium atrovirens, but the fruit is 

 different. The sclerotia eventually produce numerous black 

 bristles, also hyaline conidia borne at the tip of hyaline 

 conidiophores. According to the author the sclerotia become 

 converted into a pycnidium at certain times, at others the 

 fruit oscillates between Phoma, Gloeosporium, and Colleto- 

 tricham. The mean of all these forms is described as follows 

 by the author. 



Ver?nicularia varians (sp. nov.). Pycnidia erumpent and 

 superficial when mature, 75-150 /*, mouthless, furnished with 

 black, rigid hairs, 100-130X3-4 AS biseptate, slightly swollen 

 at the base, attenuated and pale at the summit. Conidia 

 slightly curved, acuminate, hyaline, guttulate, 18-22 X 2*5-3 /x ; 

 co'nidiophores hyaline or brown at base, 20-30x3-3*5 fi. A 

 variable species. 



Ducomet, Ann. t Ecole Nat. d'Agric. de Rennes, 1909, p. 24. 



PYRENOCHAETA (De Not.) 



Perithecium globose, partly immersed in the matrix, 

 blackish, furnished round the mouth with spines; spores 

 continuous, elongated, hyaline. 



Often occurring on the stems or leaves of herbaceous 

 plants. Considered as saprophytes generally, but in all 

 probability many of the hosts are infected while in a living 

 condition, the fruit of the fungus only appearing after death. 



