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’. 
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withdrawn by isolation from the influence of 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. FIG. 46. Sphacria Scirpi. A the ascus after elongation 
with the ruptured outer membrane at the base and the 
= } a 7 j spores not yet ejected. 3 the last spore of an ascus 
With regard to the Lichen-fungi which spars net vst ciected._ the last spore of = 
5 = 4 7 ejected are immediately above it. C ascus emptied of its 
have perithecia, we only know that ejection spores. From Pfeffer's Physiology, after Pringchein. 
from their asci also takes place?, 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 *, 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 

1 Tulasne, Mém. sur les Lichens (Ann. d. sc. nat. ser. 3, XVII). 
? Tulasne, 1. c.—Stahl, Beitr. z. Entwickelungsgesch. d. Flechten, II, 1877. 
3 Jahrb. I, 189. 
