THE FUNGI WHICH CAUSE PLANT DISEASE 159 



spreading the fungus during the summer though they have not 

 yet actually been observed to germinate or to cause infection. 



Apothecia radiately arranged on the stroma which is about 

 0.5-1.5 cm. across; asci 

 120-130 X 9-10 ix; spores 

 large, 65-80 Tt 1.5-3 m; 

 paraphyses numerous, in- 

 curved or hooked. 



Conidia (=Melasmia 

 acerina Lev.) preceding 

 the asci, producing numerous 

 small, hyaline, 1-celled 

 spores in an extended hy- 

 menial layer. 



On various species of Fig. 

 maple, apparently consist- 

 ing of races since in different localities the host differs without a 

 crossing over of the fungus. 



R. punctatum (Pers.) Fr. also occurs on maple, especially Acer 

 pseudoplantanus. It may be distinguished from the preceding by 

 its small, speck-like stromata. 



R. salicinum (Pers.) Fr. is found on willow in Europe and 

 America. It is quite similar in external appearance to R. acerina 

 except for the smaller average size of the spots. 



R. symmetiicum MflU. is another willow inhabiting species. 

 The apothecia are amphigenous and are said to mature in autumn 

 on the still live leaves. 



Other species are common especially on various Ericaceae and 

 Coniferse in Europe and America. 



113. — R. acerinum. f , conidial layer; 

 E, ascus and paraphyses. After Tulasne. 



Hysteriales (p. 124) 



Small species with elongated, black, covered apothecia which 

 open by a long narrow slit exposing the hymenium; asci 8-spored; 

 spores usually long and slender. Some few are leaf parasites but 

 most are wood saprophytes. Pycnidia are found in some species. 

 The order serves as a bridge between the Discomycetes and the 

 Pyrenomycetes. About four hundred species. 



