244 



THE ASCOMYCETES 



causing a destructive disease called needle cast. The disease is 

 world-wide in its distribution and is especially serious on young 

 trees in the nursery. The characteristic symptom of infection is 

 premature shedding of the needles; in severe attacks all the green 

 needles may fall before May. 



Infection of the needles occurs from germinating ascospores by 

 penetration of the stomata. There follows the formation of a 



Fig. 96. Various Hysteriales. A. Habit sketch of Hysteriwn piilicare as it 

 occurs on birch bark. B. Single hvsterothecium, surface view. C. Ascus 

 and paraphysis. D. Ascospore. E. Habit sketch of Hysterograph'nnu 

 ■fraxini. F. Ascus and paraphysis. G. Ascospore. H. Conidial or Septo- 

 nema stage. /, /, and K. Mytilidion scolecosporwji. (Adapted from Loh- 

 man.) /. End view of section of hvsterothecium. /. Ascospores. K. 



Conidial or Septonema stage. 



subcuticular or subepidermal stroma; in this are developed spores 

 which have been shown [Jones (1935)] to function as spermatia. 

 Jones describes the initiation of ascogonia as occurring in the 

 summer, whereas the hysterothecia become evident during the 

 winter, and ascospores are discharged the following spring. The 

 most extensive studies of the disease and of the growth of the 

 fungus in pure culture are those of Haack (1911). 



In the family Hysteriaceae, which includes saprophytic forms, 

 the fruiting bodies are freely exposed at maturity and are formed 

 singly or are united in a stroma. The hysterothecia throughout 

 the family are black and carbonaceous. The group has been 



