290 PART IV. CLASSIFICATION. 



been observed: the oospheres, however, all become oospores. The ger- 

 mination of the oospores presents the same variations as in the Perono- 

 sporacese. 



Saprolegnia can be obtained by placing dead flies in water from a ditch 

 or pond: in a day or two the flies will be found covered with mycelium, 

 if the temperature has been sufficiently maintained. 



Sub-Class IV. ASCOMYCETES. This sub-class includes a 

 vast number of forms, both saprophytes and parasites. Some of 

 them (e.g. Penicillium glauctim, Eurotium Aspergillus) are fami- 

 liar as the blue or green moulds appearing on jam, damp boots, etc. ; 

 others (Erysiphese) as mildew on roses, etc. : Cordyceps infests the 

 larvse of insects. 



In some cases the life-history is complicated by polymorphism, 

 including one or more entirely asexual conidia-bearing forms. 

 These various life-histories are briefly illustrated by the following 

 examples. 



In some cases (e.g. Eremascus albus, Gymnoascus, most Asco- 

 mycetous Lichen-fungi, Ascobolus furfuraceus, Pyronema) the 

 life-history is perfectly simple, presenting only the plant bearing 

 sexual organs, and, subsequently, the ascocarp. On germination 

 the spores (ascospores) produced in the ascocarp give rise to the 

 plant. 



In other cases (e.g. Erysiphese, Eurotium, Penicillium) the plant 

 reproduces itself by means of conidia ; in the Erysiphese and Euro- 

 tium it generally produces sexual organs eventually ; but in 

 Penicillium the formation of sexual organs takes place only excep- 

 tionally under special conditions, so that many successive genera- 

 tions may be produced by means of conidia before a sexual plant 

 makes its appearance. This may occur also in the Erysiphese. 



A more complicated life-history can be clearly traced in Clavi- 

 ceps purpurea, the Ergot of Rye. The mycelium is developed 

 in the ovary of the Rye-flower, and forms a continuous layer 

 of hyphse, a compound conidiophore, at the surface, from which 

 immense numbers of conidia are formed by abstriction, imbedded 

 in a mucilaginous substance known as Honey-dew. This substance 

 is eaten by insects, and thus the conidia are carried to other 

 flowers and there reproduce the fungus. This is the Sphacelia- 

 form. When the rye is ripening, the mycelium forms a dense 

 sclerotium (see p. 277), fusiform, about an inch long, of a dark purple 

 colour at the surface. This is the Ergot, and it remains dormant 

 until the following spring. On germination the sclerotium gives 



