308 CLASS ASCOMTCETEAE 



Asexual reproduction is lacking or consists of the formation of single 

 conidia or the successive formation of conidia which may separate as fast 

 as formed or remain adherent in chains, the oldest conidium being the 

 terminal one. In the Capnodiaceae and Meliolaceae conidia may be 

 produced in pycnidia. The perithecia arise on the external mycelium or 

 may be partly surrounded by it except in a few cases where they are sub- 

 cuticular or subepidermal, becoming external through the rupture of the 

 cuticle or epidermis respectively. They do not possess an ostiole in the 

 Erysiphaceae but in the Capnodiaceae ostiolate and inostiolate species 

 occur, in some cases both in the same genus. 



Following Theissen and Sydow (1917) this order may be divided into 

 five families as follows : 



Erysiphaceae: external, mycelium white (cinnamon-yellow in Astomella), con- 

 idia hyaline, falling off singly or more often remaining attached in chains. 

 Perithecia without ostioles, external to the host, free or embedded in cottony 

 mycelium, external layer of peridium dark-colored, brittle at maturity, the 

 cells polygonal in outline, with various types of hyphal appendages. Asco- 

 spores hyaline (or yellow in one genus). 



Meliolaceae: external mycelium colored, reticulately branched, the individual 

 cells cylindrical (not forming a moniliform hypha), sometimes with spines 

 and hyphopodia, not becoming slimy. Conidia mostly in ostiolate pycnidia. 

 Perithecia external (subepidermal in one genus), usually without true ostioles, 

 external cells polygonal, not becoming slimy. Perithecia without true ap- 

 pendages but often with bristles arising from an overlying layer of spiny 

 mycelium. Ascospores rarely one-celled, mostly two- to several-celled, 

 hyaline or more often brown. 



Englerulaceae^: external mycelium mostly colored, parasitic on leaves or on 

 fungi on the latter. Chief distinction is the release of the asci from the peri- 

 thecia by the slimy histolysis of the latter. 



Capnodiaceae: external mycelium of dark moniliform hyphae or of straight- 

 sided hyphae united laterally into dark sheets. In many cases saprophytic 

 on "honeydew." Conidia in elongated ostiolate pycnidia. Perithecia dark, 

 with or without ostioles, sometimes in the same genus. Walls of the often 

 stalked perithecia of rounded cells or of longitudinal hyphae united by slime. 



Trichothyriaceae : mycelium dark-colored, creeping over the epiphyllous my- 

 celium of Meliola and other fungi. Perithecium wall of radial hyphae, origi- 

 nating at the tip of an upright hypha which then turns over so that the 

 morphological base of the perithecium is uppermost with the clusters of asci 

 at the upper end. Ascospores two- to several-celled, hyaline or colored. 

 Very doubtfully belonging in this order is the following: 



Atichiaceae: forming small rounded or stellate cushions on leaves, horny when 

 dry, gelatinous when wet, with no free mycelium. Reproducing asexually by 

 clusters of cells (propagula). Perfect stage consists of asci scattered here 

 and there in one level in thickened areas of the thallus. 



Arnaud (1925) does not recognize this order but distributes the 

 families here included among various other groups. Thus he places the 



*See note on this family on p. 319. 



