350 



BOTANY 



-Protomyces pachydermus. 1, Mycelial 

 filament (m) with chlamydospores (cZ) ; 2, 3, ger- 

 minating chlamydospores bearing sporangia ; 

 4, the extruded spores ; 5, spores (a) germinated . 

 in a nutrient solution and abstracting yeast- 

 like conidia (b) by budding. (After Brefeld, 

 1 X 120, 2, 3 X 200, 4, 5 X 320.) 



plasm into numerous small spores, which are eventually discharged (4). Brought 



into a nutrient solution, the spores ger- 

 minate directly and produce, without 

 previously forming a mycelium, oval 

 conidia which by a continuous pro- 

 cess of budding give rise to new con- 

 idia (5). Such a method of multi- 

 plication of conidia by budding is 

 termed yeast budding, and the 

 conidia are termed YEAST conidia. 

 The yeast-like conidia thus arising by 

 the budding of the conidia of Proto- 

 myces continue this mode of repro- 

 duction until brought in contact with 

 the host-plant, when they give rise to 

 a mycelium penetrating its tissue. 



Many of the higher Fungi, in addi- 

 tion to their regular, asexual fructi- 

 fications, produce similar yeast -like 

 conidia when the conditions for their 

 nutrition are favourable. Such yeast- 

 ■ like conidia are in fact often found in 

 nature freely growing in any sugary 

 medium. As regards many of them 

 it is impossible to say definitely from 



what higher Fungus-form they have been derived. 



Such yeast conidia are represented by the beer, alcohol, and wine 

 yeast, and are included in the genus Saccharomyces. These Fungi are espe- 

 cially remarkable on account of their power of exciting alcoholic fer- 

 mentation in saccharine solutions. S. cerevisiae is the beer yeast used 

 in brewing, and is known only in its cultivated form. S. ellipsoideus, 

 which causes the fermentation of grape-juice in the manufacture of 

 wine, occurs regularly, on the other hand, in the soil of vineyards ; 

 it is therefore always present on the grapes and need not be added 

 to the grape-juice. S. mycoderma forms a whitish-gray scum {fleur de 

 vin) on the surface of wine and beer, which causes their decomposi- 

 tion. 



The conidia of the Yeast Fungi are oval in shape and contain a nucleus. 

 They increase in number by a continuous process of budding (Fig. 2, p. 11). When 

 the substratum has become exhausted by repeated budding, the yeast cells are 

 converted into sporangia which, while externally resembling conidia, give rise 

 to a number of spores. As the size and number of these spores are not always the 

 same, the Saccharomycetes are classified with the Jlemiasci. 



According to the recent investigations of J6egensen, the yeast cells causing the 

 fermentation of grape-juice are produced by the branched filaments of Mould Fungi 

 which vegetate on the surface of the grapes and form numerous conidia {Dematium 

 and Ohalara stages). 



