CHAPTER VIII. THE THALLOPHYTA. 



3 T 5 



The principal divisions of the Ascomycetes are the Erysiphece, 

 the Tuberacece, the Pyrenomycetes, and the Discomycetes. But 

 here are also classed Gymnoascus, a small fungus often found on 

 the dung of horses and other domestic animals, and which pro- 

 duces a very simple fructification, consisting of short, branched 

 filaments, bearing several unenclosed asci. Here also are placed, 

 provisionally at least, the Saccharotnycetes or Yeast-fungi, and the 

 apparently related Exoascus, one species of which produces the 



disease called " bladder-plum," in the 

 fruits of various species of Prunus. 



The Erysipheae include the 

 common mildew or blight, Penicil- 

 lium glaucum, found frequently on 

 mouldy bread, and various other de- 

 caying matters ; Erysiphe Tuckeri. 

 one of the destructive blights that 

 infest the grape ; 

 and Eurotium re- 

 pens and Eurotium 

 Aspergillus-glaucus, 

 the mildews most 

 common on pre- 

 served fruits. In 

 these the fructifica- 

 tions are small and 

 usually rounded, consisting of a few asci enclosed in a false 

 parenchyma tissue. Some of them, however, for example, Peni- 

 cillium glaucum, only exceptionally produce an ascosporous 

 fructification, reproduction ordinarily taking place by means of 

 conidia. See Fig. 513. 



The sexual and asexual modes of reproduction in Eurotium 

 repens are illustrated in Fig. 514. 



The Tuberaceae are, many of them, highly prized for food, 

 under the name of Truffles. They produce subterranean, tuber- 

 like fructifications from a mycelium that penetrates through the 

 soil, and, in some instances at least, is parasitic on the roots of 

 trees. The fructification is usually spheroidal, and invested with 

 a tough cortical layer. The ascospores are produced in intri- 

 cally winding passages in the interior. Each ascus contains 



Fig. 513. — Penicillium glaucum. a, mycelium : b, con- 

 ldia-beanng hypha : c, conidia. Magnified about 150 

 diameters. 



