224 COMPARATIVE MORPHOLOGY OF FUNGI 



irregularly scattered. In them are the germs of two characteristic 

 groups which are significant for the later development of the whole 

 order. On the one hand, there is the differentiation of the stroma into 

 a fertile and sterile part (Kusanoopsis-Myriangium series), on the other 

 the localization of the asci into a single layer (Myriangium Duriaei-M. 

 Thwaitesii) . 



The further development of the Myriangiales takes place in the two 

 directions marked by the families of the Plectodiscellaceae and Saccardi- 

 aceae. In the Plectodiscellaceae the irregular arrangement of the asci is 

 retained; the stromata, however, form a special rind crust which develops 

 on the upper side to a true cover plate. In the Saccardiaceae, however, 

 the original irregular arrangement of the asci is lost and is replaced by a 

 single palisade-like ascigerous layer; the homogeneous structure of the 

 stromata, characteristic of the Myriangiaceae, is retained in them; the 

 formation of a rind crust or cover plate is notably absent. 



By an increase in number and elongation of asci (transition from 

 spherical to clavate form) the Saccardiaceae may have given rise to the 

 lower Dothioraceae, whose stromata, indefinite in form, as in the Saccar- 

 diaceae, are pulvinate. but whose interthecial stroma has become com- 

 pressed to thread-like pseudoparaphyses by the maturing asci. Besides 

 this degeneration of the interthecial core, there appears a tendency in the 

 lower Dothioraceae, as in the Kusanoopsis-Myriangium series of the 

 Myriangiaceae, to differentiate the stromata into sterile and fertile parts, 

 i.e., to restrict ascus formation to definite fertile parts, the conceptacles, 

 which become increasingly independent. 



This individualization of conceptacles has proceeded in two direc- 

 tions. Each stroma of the higher Dothioraceae develops several concep- 

 tacles which gradually emerge from the stromatal surface, finally dividing 

 it into a sterile basal stroma and a sessile, external fructification, the 

 perithecium. In the Pseudosphaeriaceae only one conceptacle is formed 

 in each stroma, which is reduced to a single perithecium. In both the 

 higher Dothioraceae and the Pseudosphaeriaceae the individualization 

 of the conceptacles and formation of a special perithecial wall is accom- 

 panied by a gradual differentiation of an ostiole, also by an entire gelifica- 

 tion of the interthecial ground tissue and the formation of true paraphyses. 

 As a result of these two developmental processes, the forms entirely 

 lose their Myriangial character and join the higher orders. 



In these varied developmental forms lie the roots of a whole series of 

 higher Ascomycetes. Hence in no less than five different orders, the 

 Sphaeriales, the Dothideales, the Hemisphaeriales, the Phacidiales and the 

 Pezizales, we will have to refer to the relationships of the Myriangiales. 



