ORDER HYPOCREALES 287 



how is not known because certain stages were missed in the investigation, 

 to a series of binucleate cells which develop into ascogenous hyphae and 

 form asci by the hook method. 



The 60 or more genera making up the order are variously assigned to 

 one family, to three families, or to still more. The basis of distinction is 

 the presence or absence of stromata, the location of the perithecia, and 

 the type of the ascospores. A number of genera with perithecial cavities 

 in a stroma but without well-developed perithecial walls, and w^th long 

 slender ascospores and lacking paraphyses, seem to constitute a natural 

 well-defined family, the Clavicipitaceae. Those with ascospores not of this 

 type and with distinct perithecia buried in the stroma are usually called 

 the Hypocreaceae, while those with perithecia external, with or without a 

 stroma, are placed in the Nectriaceae. The following genera should be 

 noted : Nectria has perithecia external to the substratum or to an external 

 stroma on the substratum, round with short ostiolar papilla or none, 

 usually light-colored, asci in a tuft at the base of the perithecial cavity, 

 ascospores two-celled, hyaline. Often parasitic on twigs or other plant 

 tissues. In some species, e.g., N. cinnabarina Fr., there first arises a cush- 

 ion-like pseudoparenchymatous stroma which bears on its outer surface 

 a dense layer of slender conidiophores, each bearing a small ellipsoidal 

 spore {Tuhercularia stage). Later around the base and eventually all over 

 the stroma arise the round, rather thick-walled perithecia from whose 

 ostioles escape the ascospores. Over 250 species of Nectria have been de- 

 scribed. The presence or absence of the stroma has been used by some 

 mycologists to distinguish two genera. Hypomyces, with 50 or so species, 

 produces a felt-like stroma or subiculum over the surface of various species 

 of Agaricaceae, Polyporaceae, etc. The perithecia are essentially like those 

 of Nectria except for the presence of the stroma or subiculum. Gihherella 

 produces its blue- or violet-colored perithecia on the stems, grains, etc., of 

 various plants. Its ascospores vary from two to several cells. G. zeae 

 (Schw.) Fetch {G. sauhinetii Oud.) is the cause of scab and root rot of 

 wheat and other cereal grasses and of the root rot of maize. Its asexual 

 reproduction is by the abundant production of several-celled, sickle- 

 shaped conidia {Fusarium stage). Subsequently the perithecia appear. 

 Sphaei'ostilbe has perithecia and ascospores as in Nectria but these arise 

 around the base of a stalked conidial head of the Stilbella type. It is mostly 

 parasitic on scale insects and other insects infesting the twigs or leaves 

 upon which the fungus occurs. Polystigma develops its perithecia in 

 stromata within the host leaf. Hypocrea has perithecia much like those of 

 Nectria, but buried in the bright-colored stroma Avhich resembles in many 

 ways that of Hypoxylon of the Xylariaceae. Over 110 species are known. 

 In the Clavicipitaceae may be mentioned Epichloe whose stroma develops 

 as a thick white band around the stems of various grasses. In this white 



