MICROTHYRIACEAE 237 



3. Ascomata and assimilatorv hvphae superficial Alicrothyriaceae 

 2. Mycelium membranaceous and radially anastomosed 



Trichopeltaceae 

 1. Fructification (shield) not composed of radially arranged elements 



Hemisphaeriaceae 



Little regarding the developmental history of Hemisphaeriales 

 is known, and generalizations concerning them will be possible 

 only when a reasonably large number have been adequately 

 studied. Studies of their gross structure, such as those of Arnaud 

 (1918), have been made by using herbarium specimens. Al- 

 though such studies are very valuable, they are not sufficient to 

 establish relationships ^\'ithin the order or to determine their 

 phylogeny. 



Stigmateaceae. The Genus Stigmatea is the best-known rep- 

 resentative of this family. Klebahn (1918) studied several 

 species, including S. robertiani, occurring on Geraniiini roberti- 

 animt. He noted that this species forms leaf spots during late 

 summer and fall and that the pathogen forms a membranaceous 

 layer beneath the cuticle. During the winter this layer thickens 

 at certain points, these thickened areas (stromata) becoming 

 fructifications that mature in the spring. Killian (1922) described 

 the occurrence within youns^ stromata of a uninucleate anther- 

 idial cell and a uninucleate ascogonial cell whose protoplasts 

 fused through a papillar passage. After several divisions of each 

 of the nuclei, fusion in pairs took place; the diploid nuclei then 

 migrated into ascogenous hyphae arising from the ascos^onium. 

 Several functional asco^onia may be formed within each stroma. 

 It is probable that this type of sexual apparatus does not occur 

 in all species of Stigmatea, for in S. potentillae conceptacles that 

 appear to be spermogonia have been observed. 



MicROTHYRiACEAE. In this family the radiate nature of the 

 fructifications is best developed. The position of the family has 

 been much in dispute, however, as is indicated by the fact that 

 in Sylloge Fiingonnn Saccardo placed it first among the Dothi- 

 deales; then it was shifted among the Ervsiphales; and finally 

 Theissen (1913, 1913a) and Theissen and Sydow (1917) included 

 it in their new order, Hemisphaeriales. Doidge (1920) and Ryan 

 (1926) accept this classification among the Hemisphaeriales, but 

 Arnaud (1918) would place it near the Myriangiales. 



Ryan (1926) found that the ascocarps of Microthyriaceae may 

 arise either from a mycelial cell, a hyphopodium, a lateral my- 



