292 CLASS ASCOMTCETEAE 



ing the validity of the assumption of such intermediate forms, drawing the 

 distinction not so much on the external and structural characters of the 

 wall as on the nature of the hymenium. If true paraphyses (the meta- 

 physes of Petrak) arise from the floor of the perithecium among the slen- 

 der mostly parallel asci, ending free above, these are to be considered as 

 true Sphaeriales, while the spreading broader asci which entirely crowd 

 hack the stromatic tissues, or the rather broad, thick-walled asci which 

 arise in monascous cavities, leaving paraphysis-like threads attached both 

 above and below, indicate their connection to the Pseudosphaeriales, even 

 if the external structures are similar. Unless the latter position is taken 

 we have the anomaly of one genus, Leptosphaeria, with some species con- 

 sidered as Pseudosphaeriales, others as intermediate forms, and still 

 others as true Sphaeriales (Petrak, 1923, Gaumann, 1928). The forms 

 with more massive stromata which have at maturity several cavities 

 would find their place better in the Dothideales. Where these perithecium- 

 like stromatic structures arise separately or crowded in clusters we have 

 the Pseudosphaeriales. Where the stromata have been developed super- 

 ficially on the leaves of the host they are mostly small, hemispherical or 

 disk-like, with the upper surface firmer and the lower portion less firmly 

 developed. They open at the top by a more or less tearing of the tissue. 

 In the interior there may be separate monascous cavities or the central 

 tissues may be dissolved, as in some of the Pseudosphaeriales, leaving a 

 cavity with a cluster of aparaphysate asci. Such fungi form the Order 

 Hemisphaeriales, perhaps the majority of which were formerly included 

 in the old Order Perisporiales. Von Hohnel considers some of the Micro- 

 thyriaceae to be related to Meliola in this latter order. 



The more massive stromatic Myriangiales do not show such similar- 

 ities to the Sphaeriales as either of the foregoing orders. Studies by Miller 

 (1938) demonstrate that this order formerly associated with the Pseudo- 

 sphaeriales does not belong here but has its closest relationship with the 

 Aspergillales next to which order they are given consideration. 



Order Hemisphaeriales. The older interpretation of the fruit bodies 

 was a perithecium with the basal portion poorly developed while a more 

 or less shield-shaped perithecial wall formed the upper half. It is now 

 interpreted as a stroma with a hyphal or pseudoparenchymatous basal 

 portion and a firmer upper part. At the apex, by breaking of the tissues, a 

 pseudo-ostiole is often formed. Another view which once received strong 

 support on the part of a number of mycologists was to consider this struc- 

 ture as a small apothecium with a poorly developed hypothecium and 

 with a more or less permanent and rather late-opening cover, as in the 

 Phacidiales, to which by this theory the order was believed to be related. 

 Theissen and Sydow (1917) held this viewpoint and von Hohnel (1919) 

 believed that certain Microthyriaceae are forms transitional to the 

 Discomyceteae. The order consists of fungi which are entirely superficial 



