458 



A TEXTBOOK OF BOTANY 



[Ch.X 



sexual fusion. There results a rounded perithecium, in 

 which 8-spored asci are scattered amongst hyphal fila- 

 ments, the spores being later set free by decay of the wall. 

 The Blue Mold (Penicillium glaucum) occurs abundantly 

 upon bread intermixed with Black Mold, and in other situ- 

 ations; and it has a certain utility in its power to give, 

 through by-products of its own growth, the peculiar flavor 

 to Roquefort cheese. 



Order 5. Exoasci: the Naked-ascus Fungi. These are 

 small and simple parasites, 80 in number, which cause deform- 

 ities in plants. Thus, Exoascus deformans produces the curl 

 of Peach leaves ; another causes abortion of pits, and blad- 

 dery swelling in plums (Fig. 320) ; and others (Taphrina) 

 induce small growths of Witches' Brooms 

 (page 198) on some deciduous shrubs. 

 Their mycelium develops perennially in 

 the epidermis of the host, and forms on 

 the surface many 8-spored asci, which 

 appear as gray, powdery films. This is 

 the only mode of reproduction in the 

 group, and no sexual structures whatever 

 are known. Thus these plants are among 

 the simplest, and presumably most degen- 

 erate, of all Ascomycetes. 



IQOc 



1/ u \r 



Taph- 

 on a 



Fig. 320. 

 rina Pruni 

 plum ; X 400. 



The mycelium 

 shows in cross section 

 in the epidermis. The 

 ascospores abstrict 

 conidia. (After Sade- 

 beck, from Stras- 

 burger.) 



Order 6. Saccharomycetes : the 

 Yeasts. These are microscopic simple 

 plants, well known through their connec- 

 tion with the raising of bread and the 

 production of alcohol by fermentation, as 

 already fully explained (page 169). Only some 50 species 

 are known, but they have great economic importance. 



In typical Yeasts (Fig. 321), the plant body consists of a 

 single ovoid, colorless cell, possessing cytoplasm, nucleus, and 

 sap cavity within a thin wall. In nature they live sapro- 



