ORDER DOTHIDEALES 291 



laceae with the Hemisphaeriales and the Montagnellaceae with the 

 Pseiidosphaeriales. This leaves but the single family Dothideaceae with 

 about 34 genera and over 100 species. 



The two orders Hemisphaeriales and Pseudosphaeriales are stromatic 

 forms, without true perithecia. In these the asci arise from ascogenous 

 hyphae developed in the midst of a more or less pseudoparenchymatous 

 stromatic tissue. These ascogenous hyphae spread through this stroma 

 making their way by pressure and by dissolution of the tissues, eventually 

 forming cavities within which single asci are produced, separated from one 

 another by a thinner or thicker remnant of the original stromatic tissue. 

 In some cases these stromatic remnants entirely disappear so that a clus- 

 ter of asci arises in the cavity dissolved by their actions in the stroma, as 

 in the Dothideales. The chief difference from the latter is that but one 

 such locule is formed in a perithecium-like stroma instead of many locules 

 in a more massive stroma. The intervening stromatic tissue, where the 

 asci are close together in monascous cavities, was in many cases formerly 

 mistaken for paraphyses but can be distinguished by the fact that it is 

 fastened above as well as below, and often laterally. Those forms in which 

 the "paraphyses" are described as attached reticulately to each other 

 belong in this series as do those where their tips form a continuous pseudo- 

 parenchyma above the apices of the asci. Such structures must be sharply 

 distinguished from the epithecium found in many Tuberales and Lecano- 

 rales and in some other groups of fungi in which true paraphyses overtop 

 the asci and fuse with one another above the latter. The asci are never 

 operculate. They are usually much thickened, at least upward, and are 

 obovoid or clavate, rarely slender and cylindrical. The ascospores vary 

 from one-celled and hyaline to phragmosporous or muriform, sometimes 

 hyaline and sometimes colored. The stromata may resemble simple 

 perithecia, the central portion of the apex breaking away as a pseudo- 

 ostiole. The asci may arise parallel in a row at the bottom of the cavity or 

 they may arise in a fan-shaped cluster from a raised "placenta" at the 

 center of the base. In the latter type there are usually no paraphysis-like 

 remnants of the stromatic tissue, this having been dissolved or pushed 

 back as the asci grew, while in the former type these fragments usually 

 persist until the maturity of the asci. Petrak (1923), Gaumann (1928), and 

 others are inclined to consider all perithecium-like structures with a 

 spreading, nonparaphysate basal cluster of asci as pseudosphaeriaceous, 

 even though the spore fruit may appear to possess a true perithecial wall 

 and a typically developed ostiole lined with periphyses. Whether such 

 forms are in reality intermediate, as they believe, between the Pseudo- 

 sphaeriales and the Sphaeriales or not, will require much further investi- 

 gation to determine. It seems clear that the typical structure is very 

 different in the two orders. Perhaps Nannfeldt (1932) is right in question- 



