142 



PYRENOMYCETES 



[CH. 



Lachnea cretea and the Ascoboli, where the coiled and septate archicarp. is 

 often still functional. 



A very common initial organ in forms with embedded perithecia is the 

 short filament of cells sometimes known as Woronin's hypha (fig. 103). The 

 cells are large and contain well-marked nuclei and lie in a nest of small- 

 celled vegetative mycelium. Woronin's hypha has been found among the 

 Hypocreales mNectria and among the Sphaeriales in Xylaria and Hypoxylon ; 



it remains to be shown whether 



it still functions. It may have 

 originated from the simple archi- 

 carps of the Lower Pyrenomy- 

 cetes or by reduction from forms 

 with a multicellular trichogyne. 

 With its final disappearance we 

 reach such completely apogamous 

 species as those of Cordyceps and 

 Claviceps. 



(iii) A quite distinct type of 

 primordium has been described 

 in Strickeria, Sporormia and Pleo- 

 spora; in these cases the asco- 

 genous and vegetative filaments 

 arise from a common initial cell 

 which divides not only transverse- 

 ly, but longitudinally, forming a 

 compact tissue (fig. 104). Other hyphae may anastomose with this mass, 

 or it may give rise alone to the whole fructification. Possibly some sugges- 

 tion of its origin may be found in the peculiar, but apparently normally 

 fertilized oogonium ol Leptosphaeria. 



The Pyrenomycetes do not appear to have given rise to any higher 

 forms, and have themselves a greater vegetative development than any other 

 Ascomycetes. 



They may be subdivided as follows : 



Wall of perithecium differentiated from stroma; 



perithecium wall and stroma, if present, soft in 



texture, either colourless or light coloured HYPOCREALES. 



perithecium wall and stroma, if present, firm, leathery 



or brittle, dark in colour Sphaeriales. 



Perithecium always sunk in a stroma from the tissue of 

 which its wall is not differentiated ; colour of stroma 

 black or dark brown Dothideales. 



Minute, external parasites on insects, perithecium borne 

 on a receptacle which also bears appendages; spores 

 two-celled Laboulbeniales 



Fig. 104. iyT-zV&r/asp.; initialcellsofascocarps; 

 after Nichols. 



