208 ON THE PERONOSPOR^. 



are known under the name of Sderotium vasium, and which are 

 believed to be the mycelium of certain moulds in a high state of 

 condensation." Worthington Smith, in the Gardener's Chronicle 

 for 1880, described and illustrated a Sderotium affecting Potato 

 stems, which he thought belonged to some fungus other than 

 Peronospora. In September, 1883, Mr. Stephen Wilson 

 announced that these Sclerotia belong to Peziza postuma, and 

 that he has grown the specimens of the fungus, which he figures, 

 from Sclerotia kept and preserved by him. He queries whether 

 these are truly parasitic, or whether they do not merely follow the 

 decay of the stalks consequent on the common disease. The 

 same gentleman, in the previous year, had made a communication 

 to the Linnaean Society on the subject of certain dark, small, 

 ovoid bodies, found in the leaf of the Potato, and which he 

 considered to be parasitic sclerotia of Peronospora infestans. He 

 thought that they were amorphous particles of glutinous plasm, 

 which after a period of incubation germinate in the tissues of the 

 plant, and account for the appearance of disease independently 

 of the conidia. Mr. Murray and Dr. Flight, of the British 

 Museum, had, however, examined them, and submitted them to 

 chemical analysis, and came to the conclusion that they were 

 masses of oxalate of lime, and had no necessary connection with 

 the Potato fungus. 



But leaving this subject, there are one or two points of interest 

 to be dealt with. First of all, when did the Peronospora first 

 make its appearance ? We owe to Mr. Carruthers, of the British 

 Museum, a fossil slide, which has been described by Worthington 

 Smith as probably a fossil Perofiospora. Silicified mycelia have 

 been known for a long time occurring in fossil wood and ferns, 

 but no perfect fruit had been observed on any fossil mycelium. 

 No description, except that of a Mucor from the Coal Measures, 

 has hitherto been published of any well defined fungus belonging 

 to the Palaeozoic series of rocks. This fungus was found in the 

 scalariform axis of a stem of a Lepidodejidron from the Coal 

 Measures. The mycelium is furnished with numerous septa, a 

 characteristic supposed to distinguish Peronospora from Pythium 

 or Saprolegfiia, and the oogonia do not agree with those of 

 Cystoptis. The oogonia and zoospores are not only of the same 



