180 THE ASCOMYCETES 



Stromata, if present, and perithecia carbonaceous Sphaeriales 



Perithecial wall not differentiated from stroma, but perithecia mere 



locules in the dark-colored stromata Dothideales 



Minute external parasites of insects; ascocarps borne on a receptacle 



that may be appendaged Laboulbeniales 



Dothideales 



As described by Lindau in Die naturlichen Fflanzenjamilien, 

 the Dothideales comprise 24 genera and 400 species, all included 

 in the one family Dothideaceae. In their monographic treatment 

 Theissen and Sydow (1915) set up the order with 4 families hav- 

 ing 140 genera and containing a total of about 8000 species, a 

 large proportion of which are tropical. They later reduced the 

 order to two famihes, Dothideaceae and Phyllachoraceae. In the 

 Dothideaceae the stromata are immersed within the host and be- 

 come erumpent at maturity; in the Phyllachoraceae they remain 

 covered by host tissues. Members of the two remaining families, 

 as first used by Theissen and Sydow, have been distributed 

 among the iVIyriangiales, Hemisphaeriales, and Sphaeriales. There 

 has even been some question as to whether the Dothideales con- 

 stitute a natural order. The foregoing statements convincingly 

 indicate the confused status of the Dothideales, a chaos largely 

 traceable to the fact that the Hfe histories of less than a half- 

 dozen dothideaceous species are known. 



As employed in this work, the Dothideales are pyrenomyce- 

 tous fungi, possessing black stromata within which perithecial 

 cavities, lacking independent perithecial walls, are developed. 

 Whether the stromata remain endogenous (innate) or become 

 exogenous (erumpent) at maturity is the basis for separating the 

 two families, Phyllachoraceae and Dothideaceae. 



Dibotryon (Ploivrightia) viorbosinn, the cause of black knot 

 of" plums and cherries, is widely known, but its ordinal position is 

 not yet established. It has been placed in older accounts among 

 the Dothideales, but Theissen and Sydow (1915) regard it as 

 nearly related to Botryosphaeria, which some mycologists place 

 among the Myriangiales. Undoubtedly it is not a member of the 

 Phyllachoraceae. To shift it from the Dothideales on the basis 

 of present knowledge would only add to existing confusion. 



A study of the life history of D. morhosinn was early made by 

 Farlow (1876), and similar recent studies include those of Koch 



