HEMISPHAERIALES 307 



The Microthyriaceae include about 40 genera with about 400 species, 

 chiefly of the tropics and subtropics. Just as in the Polystomelleae- 

 Parmulineae series, a gradual transition occurs from round (Fig. 201) to 

 linear (Fig. 202) fructifications, since in Hysterostomella even the linear 

 fructifications in youth have a rounded outline. At present no species 

 of economic importance is known. 



Trichothyriaceae. — The representatives of this family (Theissen, 

 1912; Hoehnel, 1917; Arnaud, 1918) may be regarded as Microthyriaceae 

 which have become specialized for parasitism on other, especially asteri- 

 noid, fungi. The originally independent hyphae cling together in brown 

 bands (Fig. 204, D and E) which cover the mycelium of the host and 

 occasionally are confused with it. As the members of this family do not 

 themselves directly parasitize leaves, their fructifications lie on their 

 own mycelium unprotected beneath by the cuticle of the host. Conse- 

 quently the basal stromatal parts attain a more marked cover layer 

 character: they become brown and pseudoparenchymatic (Fig. 204, 7). 

 In some genera, as Loranthomyces, parasitic on the stromatic Sphaeriales, 

 the fructifications appear entirely inverted and the asci hang down from 

 the morphological base above. These inverted thyriothecia are called 

 catothecia by Hoehnel (1917). Unfortunately their ontogeny is entirely 

 unknown. 



