290 



CLASS ASCOMYCETEAE 



Fig. 94. Hypocreales, Family Clavicipitaceae. Claviceps purpurea (Fr.) Tul. Stromata 

 growing from sclerotium. (Courtesy, F. C. Strong.) 



development of the ascocarp to determine whether it is a true peritheciiim 

 or stromatic in structure. 



Order Dothideales. In contrast to the undoubted Sphaeriales, i.e., those 

 forms possessing true ostiolate perithecia with asci arising from the bot- 

 tom and sides of the perithecial wall in a common perithecial cavity, and 

 with periphyses near the ostiole and paraphyses among the asci, are a 

 large number of genera formerly more or less closely associated with that 

 order. Of these the Order Dothideales is recognized as a distinct order by 

 most mycologists. It is mostly defined as consisting of fungi parasitic 

 usually on leaves, producing endophyllous or epiphyllous stromata within 

 which arise perithecial cavities which lack definite perithecial walls. 

 Apparently in this order the ascogenous hyphae arise in the center or base 

 of the stroma and, spreading outward and upward through the stromatic 

 tissues, dissolve out cavities within which the numerous asci are produced. 

 Most of the species are tropical or subtropical, but a few forms included 

 in the order reach the north temperate zone. Theissen and Sydow (1915) 

 in their monograph of this order included four families of which all except 

 the Dothideaceae have been found to have their closer relationship with 

 other orders: the Phyllachoraceae with the Sphaeriales, the Polystomel- 



