154 



PYRENOMYCETES 



[CH. 



embedded in the substratum; from these may be traced a series of inter- 

 mediate forms culminating in the elaborate stromata and sunken perithecia 

 of the highest species. There is, in fact, a marked parallelism between the 

 Sphaeriales and Hypocreales, and it is by no means clear that the colour 

 and texture of the stroma and perithecium walls are of sufficient im- 

 portance as criteria of relationship to justify their separation, nor is it 

 indicated that the members of the families Nectriaceae or Hypocreaceae 

 resemble one another more closely than the numerous Sphaeriales, though 

 these are dispersed among a series of eighteen or nineteen families. The 

 method of classification is however convenient, and considerably more 

 knowledge will be required before a natural system of classification can -be 

 elaborated. In the meantime, the subdivisions of the Sphaeriales rest on 

 the structure and development of the stroma, the form of the ostiole, and 

 the colour and septation of the spores. As in the Hypocreales, various 

 sorts of accessory fructifications are present. 



In the first eight families of the Sphaeriales the perithecia are more or 

 less free, though they may be partly sunk in the substratum, or in a weft 

 of hyphae, or may be seated on a definite stroma. 



In the remaining ten families the perithecia are immersed either in the 

 substratum, or in a stroma which may reach considerable elaboration. 

 The most important of the eighteen families of the Sphaeriales are: 

 Perithecia free 



Peridium membranous 

 ostiole beset with long hairs often elaborately 



coiled or branched 



ostiole without long hairs; mainly coprophilous 

 Peridium leathery or carbonaceous 

 short neck 



long, sometimes filiform neck 

 Perithecia embedded in substratum 

 Perithecia immersed, upper part free 

 ostiole round 

 ostiole elliptical 



Perithecia completely immersed, ostiole only pro- 

 jecting 



peridium membranous or leathery, neck short 

 paraphyses absent 

 paraphyses present 



peridium leathery or carbonaceous, neck long 

 Perithecia embedded in stroma 



Stroma developed within substratum, differen- 

 tiated from it 

 Stroma free 

 ascospores very small, sausage-shaped and 



hyaline or light brown, unicellular 

 ascospores unicellular, rarely bicellular, dark 

 brown 



CHAETOMIACEAE. 

 SORDARIACEAE. 



SPHAERIACEAE. 

 CKRATOSTOMATACEAE. 



AMPHISPHAERIACEAE. 

 LOPHIOSTOMATACEAE. 



MYCOSPHAERELLACEAE. 



PLEOSPORACEAE. 



GNOMONIACEAE. 



VALSACEAE. 



DlATRYPACEAE. 



XYLARIACEAE. 



