322 CLASS ASCOMYCETEAE 



on the apparent!}^ upper side the tissues break away forming an ostiolar 

 opening. The outer perithecial wall is radial in its structure, resembling 

 many of the Hemisphaeriales in that particular. The ascospores are two- 

 to several-celled and colorless or brown. Trichothyrium is the first de- 

 scribed and best known genus. 



Family Atichiaceae. Because of their epiphyllous habit, apparently 

 entirely external to the leaf tissues and perhaps feeding saprophytically 

 on honeydew or parasitically on hyphae of other fungi this family may be 

 placed here, but with great doubt. There are no separate hyphae but a 

 gelatinous mass of anastomosing threads forming a cushion or a stellate 

 thallus. The cell walls are very much swollen so that when moist the 

 organism is gelatinous, when dry horny. The outer layer of cells has 

 dark-colored outer walls. In separate pockets (Phycopsis) or clustered in 

 basket-like structures (Atichia) certain cells divide and form a mulberry- 

 like or tetrahedral cluster of adherent cells (propagula) which eventually 

 are pushed out by the pressure of the underlying propagula or vegetative 

 tissues and which serve to establish new plants. These propagula are 

 dark-colored externally, hyaline within. In one species spermogonial 

 structures are known, but their function has not been determined. The 

 asci arise in more or less thickened cushion-like areas of the thallus. They 

 lie separate from one another in the tissue of the thallus, arising possibly 

 from ascogenous hyphae in among the other vegetative hyphae. As they 

 mature they elongate and push through the surface and discharge their 

 eight, two-celled, hyaline or slightly colored spores. The occurrence of asci 

 scattered in the tissues of the thallus led to the suggestion by Raciborski 

 (1909) that they are related to the Myriangiaceae, while on the contrary 

 von Hohnel (1910) placed them in the Saccharomj^cetaceae. Mangin and 

 Patouillard (1912), Cotton (1914) and Arnaud (1925) have also given 

 attention to these fungi. (Fig. 103.) 



Order Aspergillales (Plectascales). This group is perhaps heterogene- 

 ous as regards certain of the included families. It shows similarities to the 

 Erysiphales and to some of the Sphaeriales and Hypocreales in its mode of 

 sexual reproduction as well as in the conidial formation. The chief differ- 

 ences lie in the internal structure of the perithecium. In the groups just 

 mentioned the ascogenous hyphae are of about the same length and arise 

 from one or more centers from which they radiate, resulting in the forma- 

 tion of a tuft or tufts of asci in the cavity of the perithecium or stroma, or 

 of a hymenium at the base and sides. The thin-walled cells making up the 

 interior portion of the perithecium or stroma give way before the out- 

 growing asci and eventually disappear completely or nearly so or the asci 

 and paraphyses grow out into the perithecial cavity. In the Aspergillales, 

 on the contrary, the ascogenous hyphae are of varying lengths so that 

 instead of arising in a tuft the asci are produced scattered throughout the 



