126 CLASSIFICATION OF THE MICRO-ORGANISMS. 



animals. Friinkel* was unable to diminish their patho- 

 genic properties hy the continued action of abnormally 

 high temperatures. He cultivated Aspergillus fumigatus 

 for half a year at 51 C., numerous re-inoculations 

 being made; under these circumstances the fungus 

 formed only a sterile mycelium, and it was necessary to 

 continue the cultivations from this mycelium. When 

 however it was placed at a temperature of 37 C., the 

 fungus at once began again to fructify, and the spores 

 formed proved to be as virulent as others cultivated 

 Distribution in the ordinary manner. All these fungi appear to 

 agpergiUi. be very widely distributed in our climate. According 

 to Siebenmann, it is only necessary to expose freshly 

 baked brown bread to the air for a short time, to place it 

 then in a moist chamber and to regulate the temperature at 

 various heights ; according to the temperature, it is found 

 that either on the surface or in the interior of the piece 

 of bread one or other form of aspergillus has developed. 



Erysiphe oidium. 



Erysiphe forms the mould-like covering on living 

 plants which is known as mildew. Summer and winter 

 spores are developed ; the former have the appearance of 

 oval unicellular conidia which are formed by segmenta- 

 tion on single upright fruit hyphffl ; the winter spores 

 are formed in the perithecia which arise at a late period 

 on the same mycelium, and they are only able to ger- 

 minate after a period of repose. The fructification by 

 conidia was formerly described as a separate species of 

 fungus under the name oidium. In the case of some 

 forms of oidium the corresponding perithecial fructifi- 

 cation has not yet been found. Mildew attacks the 

 most various kinds of plants, and the different species of 

 plants have their particular forms of mildew. The plants 

 which are attacked droop and die early. Damp weather 

 in the latter part of summer and autumn and moist 

 situations are favouring conditions. 



Two important kinds of oidium whose perithecia are 

 as yet unknown belong to this group. 



* Deutsche rued. Wochenschrift, 1885, No. 31. 



