CHAPTER III. — SPORES OF FUNGI. 



93 



Section XXV. In most Lichen-fungi with open hymenia the mechanism for 

 the ejection of the spores is similar to that which has now been described, though it 

 differs from it in particular points which appear to me to require further investigation. 

 The structure of the hymenia is essentially the same as in the Discomycetes ; there 

 is, according to Tulasne, the same turgescence of the mature ascus in both, and the 

 same simultaneous ejection through one or more longitudinal fissures in its apex 1 . 

 The asci are emptied one after another as they ripen, and the spores, according to 

 Tulasne, are flung outwards to a distance of about one centimetre; the sudden discharge 

 of many asci at once has not been observed. The differences alluded to above are, that 

 the apices of the asci do not project above the surface of the hymenium but continue 

 on a level with it or a little beneath it, and that the pressure on the asci from without 

 appears to be a chief cause of the bursting of 

 the asci and of the ejection of the spores. 

 The ejection of the spores is in fact due to 

 the action of water, which causes a con- 

 siderable swelling throughout the gelatinous 

 hymenium in the direction of its surface, and 

 consequently a lateral pressure on its turges- 

 cent asci. The pressure is moreover increased 

 by the resistance which is offered to the 

 superficial enlargement of the hymenium by 

 the thallus which bears it, and which has less 

 capacity for swelling by absorption of water, 

 or by special thallus-margins or excipula 

 circumscribing the hymenium, which, as 

 Tulasne has shown, bend in such a manner 

 when they absorb water, that they directly 

 oppose the enlargement of the surface of the 

 hymenium. Ejection of spores from an ascus 

 withdrawn by isolation from the influence of 

 these pressures, such as easily occurs in other 

 Discomycetes, has never been observed, so 

 far as I know, in any Lichen-fungus. 



With regard to the Lichen-fungi which 

 have perithecia, we only know that ejection 

 from their asci also takes place 2 , but the 

 mechanism has not been properly investigated. 



Section XXVI. Successive ejection. An isolated mature ascus of Sphaeria 

 Scirpi is a broad short club-shaped body, as Pringsheim first showed 3 , almost entirely 

 filled by its eight large spores, which are crowded together in two irregular rows. It 

 has an apparently homogeneous moderately thick wall with a double contour and 

 lined with a layer of protoplasm. Ejection takes place under water. Before it 



FIG. 46. Sphaeria Scirpi. A the ascus after elongation 

 with the ruptured outer membrane at the base and the 

 spores not yet ejected. B the last spore of an ascus 

 sticking in the fissure waiting ejection ; four already 

 ejected are immediately above it. C ascus emptied of its 

 spores. From Pfeffer's Physiology, after Pringsheim. 



1 Tulasne, Mem. sur les Lichens (Ann. d. sc. nat. ser. 3, XVII). 



2 Tulasne, 1. c. — Stahl, Eeitr z. Entwickelungsgesch. d. Flechten, II, 1S77. 



3 Jahrb. I, 1S9. 



