346 



PHYSIOLOGY OF THE FUNGI 



leave the ascus, they are directed vertically. Biiller })elieves that the 

 oblique position of the operculum is a physiological character formed as a 

 response of the ascus end to the stimulus of light. Seaver (1928), how- 

 ever, believes that the position of the operculum is not determined by 



light. 



Fig. 70. Sections through the hymeniuni of Ascobolus magnificus, showing the photo- 

 tropic response of the ascus tips to Hght. Discharge of the ascospores is then directly 

 toward the source of hght. (After Buller, Researches on Fungi, Vol. VI, p. 272, 1U34. 

 Reproduced by permission of Longmans, Roberts and Green.) 



In the development of the apothecium the paraphyses are formed 

 before the asci mature, and the developing asci push their way upward 

 among the paraphyses. In some species (Ascobolus spp., Lachnea scuiel- 

 lata) the paraphyses are straight, and only the portion of the ascus extend- 

 ing beyond the paraphyses tips responds phototropically (Fig. 70). The 

 paraphyses of others {Peziza hadia, Aleuria vesiculosa) bend toward the 

 light, and the developing asci are likewise bent as they elongate. Aleuria 

 repanda sometimes shows a coarse adjustment toward light, by the turn- 

 ing of the entire apothecium, and a fine adjustment, by the bending of the 

 ascus tips in the same direction. 



