252 



MANUAL OF POISONOUS PLANTS 



EXOASCACEAE 



This small order contains parasitic and saprophytic species. The asci are 

 without perithecium, except in Gymnoascus and Ctenomyces where there is a 

 rudimentary perithecium. The Taphrinae are undoubtedly related to the yeasts 

 and by some are placed in one order known as Gymnoasceae, being represented 

 by Gymnoascus. The Gymnoasceae exclusive of Taphrinae are sometimes placed 

 with the Plectascineae, a fungus occurring on the dung of horses and producing 

 simple-fruiting organs, which consist of short-branched filaments arising either 

 from a single hypha in which a cell is cut off, or several, one being spirally 

 wound about the other. This becomes the ascus, which contains the ascospores. 

 In Bremascus the ascus-producing part resembles certain zygospores. In 

 Ctenomyces the ascus is surrounded by simple torulose hyphae, representing a 

 rudimentary perithecium. The Bidamella spinosa described by Matruchot and 

 Dassonville is allied to Gytnnoascus. It produces numerous ovoid short stalked 

 asci with 8 ovate colorless ascospores. Parasitic on dog. The life history of 

 parasitic members of this order may be represented by Bxoascus pruni. This 

 fungus grows on the fruit of various species of the genus Prunus, producing 

 in plums what is known as plum pockets or bladder plums. The fungus, when 

 fully developed, consists mainly of a single layer of palisade-like asci, which 

 produce their branching mycelium in the parenchyma of the affected part, and 

 later develop between the outer walls of the epidermal cells and cuticle. Here 



Fig. 79. Exosceae. 1. Plum pocket iBxoascus Pruni), on Prunus Padus. a. Normal 

 iruit; b, abnormal fruit. 2. B. Alni-incaniae on alder (.Alnus incana); scales enlarged. 

 3-5. B. alnittorquus; 3. Surface view, alder leaves showing hyphae (ft) between cuticle 

 and remainder of epidermal cell. 4. Formation of asci (as). 5. Ripe asci with ascospores 

 X lOa. 1-2 after Wettstein. 3-5 after Sadebeck. 



