SPHAERIALES 277 



While the spermagonia are developing, the mycelium forms small 

 coils which produce a number of archicarps, each furnished with a trich- 

 ogyne. Subsequent development shows these structures to be 

 abortive. Perithecial development proceeds from vegetative hyphae 

 which intrude into the space bounded by an ascogonial coil which remains 

 for a considerable time during development. The ascogenous hyphae 

 develop apogamously. Apparently the process is begun by the conjuga- 

 tion of two or more vegetative cells. The nuclei of the ascogenous hyphae 

 are usually in pairs and the cytology of the ascus is normal. Meiosis 

 occurs at the first ascus division. The ascospores are divided into six 

 uninucleate cells (Jones, 1926). Kirby (1923) suggests that this species 

 is heterothallic, but Davis (1925) working with Kirby 's cultures, was 

 unable to confirm this report. 



Glomerella, also important in plant pathology, is characterized by 

 perithecia united into stromata, otherwise it is like Gnomonia. In the 

 United States, various biological strains of G. rufomaculans (G. cingulata) 

 attack the bast and fruits of numerous orchard trees and the grape. Its 

 imperfect stage is Gloeosporium fructigenum. There seems to be a slight 

 heterothallism, since single spore mycelia form abnormal perithecia with 

 difficulty. When the complementary mycelium is added, normal peri- 

 thecia are formed freely (Edgerton, 1914). 



While the Mycosphaerellaceae and Gnomoniaceae are characterized 

 among the Sphaeriales having immersed perithecia, by the perithecia 

 being solitary or, very rarely, united into stromata, as in some species of 

 Mycosphaerella and Glomerella, in the last three families of the Sphaeriales 

 to be discussed here, the Diatrypaceae, Diaporthaceae and the Xylaria- 

 ceae are distinguished by the immersion of their perithecia in a stromatic 

 plectenchyma. The two former are related to the Xylariaceae somewhat 

 as Nectria to the Mycomalus-Ascopolyporus stage; they chiefly include sim- 

 ple stromatic forms on bark whose stromata are only slightly raised from 

 the substrate, while the Xylariaceae develop fully individualized fructifi- 

 cations independent of the substrate. 



Diatrypaceae. — This family, called the Allantosphaeriaceae by 

 Hoehnel in his later treatment, is characterized by more or less colored, 

 mostly unicellular spores. The asci are 8 or many spored, clavate, 

 often with a thickened tip, long, stipitate and arranged in a hymenium 

 lining the base and sides of the perithecium. Paraphyses are usually 

 present, gelifying in age. The ostioles are sulcate. 



The simplest forms are shown by Eutypa Acharii, E. lata and E. 

 spinosa on decorticated wood. The perithecia of these species are 

 scattered singly but are united by a blackened crust on the surface of 

 the substratum. A primitive hyphomycetous stage is retained but 

 conidial locules are formed in a stroma. 



