1 54 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 ChaetOMIACEAE. 



. ostiole without long hairs; mainly coprophilous Sordariaceae. 

 Peridium leathery or carbonaceous 



short neck Sphaeriaceae. 



long, sometimes filiform neck Ckratostomataceae. 



Perithecia embedded in substratum 

 Perithecia immersed, upper part free 



ostiole round Amphisphaeriaceae. 



ostiole elliptical Lophiostomataceae. 



Perithecia completely immersed, ostiole only pro- 

 jecting 

 peridium membranous or leathery, neck short 



paraphyses absent MycosphaerellaCEAE. 



paraphyses present Pleosporaceae. 



peridium leathery or carbonaceous, neck long GnomoniaCEAE. 

 Perithecia embedded in stroma 



Stroma developed within substratum, differen- 

 tiated from it VaLSACEAE. 

 Stroma free 

 ascospores very small, sausage-shaped and 



hyaline or hght brown, unicellular DiatrypaCEAE. 



ascospores unicellular, rarely bicellular, dark 



brown XYLARIACEAE. 



