86 DIVISION I. GENERAL MORPHOLOGY. 



Zopf the uppermost spore in some Sordarieae is even attached to an inwardly directed 

 process from the membrane at the apex of the ascus. No such arrangements have 

 been observed in the majority of cases, and the apical position of the spores is 

 sufficiently explained by the consideration that the one-sided expansion of the apical 

 region must produce currents in the contained fluid in the direction of the apex, 

 which must push the spores suspended in it towards this expanding apex. 



When the wall has reached a fixed maximum of extension, it suddenly gives 

 way at a point of least cohesion near the apex, which is the point of dehiscence ; at 

 the same moment the elastic lateral wall contracts to the size spoken of above as the 

 original size, and the apical portion of the fluid contents together with the group 

 of spores is driven out through the fissure. Then the open ascus collapses and 

 perishes. 



The arrangement of the spores in the apical portion of the ascus before their 

 ejection, when there are no special arrangements for attaching and securing them, is 

 evidently the result of the conditions of space and form. In many Discomycetes for 

 instance the spores are ellipsoidal or elongated, and their length greater than the 

 breadth of the ascus ; they lie therefore parallel in the ascus, in a single longitudinal 

 row close behind one another, each placed obliquely and touching the wall of the 

 ascus with both ends, the uppermost one having its upper extremity close to the apex 

 (Figs. 39 w and 43). If the breadth of the ascus is much greater than the diameter 

 of the spores the arrangement is more irregular ; thus there is an irregular longitudinal 

 row in Ascobolus pulcherrimus l , two such rows in many Ascoboli 2 (Fig. 45), and an 

 irregular ball crowded up into the apex of the ascus in the eight-spored asci of 

 Exoascus Pruni 3 and in the many-spored asci of Ryparobius *. But the longitudinal 

 arrangement is maintained in the comparatively very broad asci of Sordaria (Fig. 44), 

 where it may be due to the attachment of the spores to one another. 



The form of the fissure varies with the species, and it cannot always be distin- 

 guished with certainty. 



A longtitudinal rent simple or lobed, passing over the apex and leaving a broad 

 hole when the ascus is emptied, forms the opening in the asci of Exoascus Pruni, 

 Peziza cupularis and Erysiphe 5 , and according to Boudier 6 of Geoglossum, Helotium, 

 Leotia, and Bulgaria sarcoides. 



In many Pezizas, as P. convexula, P. confluens, P. granulata, P. abietina, 

 P. vesiculosa, P. melaena, all the Ascoboli and Helvella crispa, the fissure is annular 

 and runs close beneath the blunt summit of the wall of the ascus, which is therefore cut 

 off like a lid, and when the spores are ejected is lifted off either all the way round or 

 only on one side where the uppermost spore touches the wall of the ascus ; the 

 latter is the case, for instance, in Peziza vesiculosa and P. granulata. In larger 

 Ascoboli the edge of the lid may be seen before the ejection of the spores as a 

 distinctly marked transverse line 7 . In some forms, as P. abietina and P. vesiculosa, 



1 Woronin, Beitr. II, t. III. 



3 Boudier in Ann. d. sc. nat. se>. 5, X. 



3 De Bary, Beitr. I, t. III. 



4 Boudier, 1. c. 



5 R. Wolff, Erysiphe ; see the literature cited in section LXXIV. 

 * Loc. cit. p. 202. 7 See Boudier's figures, 1. c. 



