CHAPTER V 



PYRENOMYCETES 



THE Pyrenomycetes include some 10,000 species; they are characterized by 

 the fact that their ascocarp or perithecium is a more or less flask-shaped 

 organ opening by a narrow pore, the ostiole, and containing a hymenium 

 spread in a regular manner 

 over the floor and lower part 

 of the sides (fig. 100). It thus 

 differs from the perithecium of 

 the higher Plectascales where 

 the asci are irregularly scat- 

 tered, and from that of the 

 Erysiphales where, except in 

 the flattened perithecium of 

 the Microthyriaceae, an ostiole 

 is not developed. By some au- 

 thors the term Pyrenomycetes 

 is used to include all these 

 groups and even certain other 

 forms, such as the Tuberales. 

 A study of the development of 

 the truffles, however, has made 

 clear their affinity with the 

 Pezizales ; the mildews consti- 

 tute a well defined and isolated 

 group, distinguished, so far as 

 they are known, by the form 

 of their sexual organs ; and 

 the higher Plectascales differ 

 from the present series and re- 

 semble the simpler forms with which they have here been classified in the 

 important character of the arrangement of their asci. 



There remain four groups, the Hypocreales, the Dothideales, the 

 Sphaeriales, and the Laboulbeniales. 



The last are true Pyrenomycetes in the sense that they possess regularly 

 arranged asci and a perithecium opening by an ostiole, but they are dis- 

 tinguished by so many special characters that, though included under this 

 heading, they can best be dealt with apart. 



Fig. loo. Sordaria sp.; ascocarp in longitudinal section 

 showing asci, paraphyses and periphyses, x 400. 



