272 CLASS ASCOMYCETEAE 



also included in this chapter. The order Erysiphales, with nonostiolate 

 perithecia, probably contains a mixture of forms with true perithecia, and 

 therefore more closely related to the Sphaeriales, and possibly some 

 Pseudosphaeriales or Hemisphaeriales as well as some Aspergillales. The 

 latter order corresponds to what Nannfeldt and others have called Plecta- 

 scales. It represents the third group. In it the asci are scattered through- 

 out the tissues of the more or less perithecium-like structure, not forming 

 in any manner what might be considered a hymenium. The Erysiphales, 

 Aspergillales, Myriangiales, and the very simple fungi forming the Sac- 

 charomycetales form the subject of Chapter 11. 



A typical perithecium consists of a more or less hollow structure whose 

 wall arises from below the sexual organs or at least from below the asco- 

 gonium, growing outward and around it and the developing ascogenous 

 hyphae, closing in at the top. Within this there is formed from the 

 ascogenous hyphae a hymenium of asci lining the perithecial wall or 

 forming a cluster at the base. Usually paraphyses arising from the 

 vegetative mycelium which produced the perithecial wall are intermingled 

 with the asci. Nearer the apex of the perithecial cavity there arise the 

 periphyses, also of vegetative origin, which converge and drive upward, 

 helping to produce the ostiole. Apparently in many cases, even in the 

 perithecia developing apart from one another, the vegetative mycelium 

 growing up over the perithecial wall forms a more or less distinct 

 stromatic layer, in which case the true perithecial wall may remain 

 colorless. This stroma may sometimes be massive, enclosing the whole or 

 the lower part of the perithecium. 



In general the Sphaeriales, Pyrenulales, and Hypocreales are parallel 

 groups that in all probability will not be maintained separately after life 

 history studies have shown the true kinships of the fungi which are now 

 included in them. They all agree in having (with very few exceptions) 

 ostiolate perithecia. Those of the Sphaeriales are dark-colored and with 

 fairly firm to hard perithecial walls or surrounding stroma. In the Hypo- 

 creales the perithecia or enclosing stroma are colorless or bright-colored 

 and are usually softer. The members of both these groups are saprophytic 

 or parasitic, usually on vascular plants, and in the rare cases where they 

 grow upon algae they do not form a lichen thallus. The Pyrenulales are 

 parasitic upon algae which they enclose in a typical lichen thallus, their 

 chief distinction from the Lecanorales being the production of perithecia 

 instead of apothecia. 



Julian Miller (1941), for many years a student of the Pyrenomycetes, 

 has had the courage to combine the Sphaeriales and Hypocreales into one 

 order under the former name, treating the latter merely as a family, the 

 Hypocreaceae, in this order. 



Many of the species, a number of genera, and several families, that 



