CHAPTER V.—COMPARATIVE REVIEW.—ASCOMYCETES, 191 
incurved so as to form a narrow-mouthed cavity. They are generally roundish 
or flask-shaped, and they are seldom more, usually less, than 1 mm. in height. 
They are- bounded on the outside by the wa// which encloses an asciferous 
hymenium, and are furnished in the full-grown state with a narrow aperture or ostiole 
(ostéolum, pore), which is a canal passing through the wall and serving for the discharge 
of the spores (section XXIII). The ostiole usually lies at the apex in reference to 
the point of origin of the perithecium, seldom at the side (Pleurostoma, Tul.) or at 
the base (Melanospora parasitica). In many species the orifice is drawn out into 
a conical or cylindrical neck (tubulus of Tode), through the middle of which the 
canal passes, and which in some cases, as in the Valseae, Sordarieae, and 
Melanospora, may be more than ı mm. in length. The asci are inside the 
perithecium on the side away from the ostiole, and are borne on the ascogenous 
hyphae or cells from which they successively shoot out, as in the Discomycetes. 
With this mode of formation it is possible for some hundreds of asci to be formed 
in the small space of some perithecia, new ones continually appearing in place of 
the ripe ones which have discharged their spores. The asci together either exclusively 
form the hymenium or are at least its most essential parts; the hymenium either 
occupies a narrow bit of surface opposite the ostiole of the perithecium, on which 
the asci grow as a small tuft parallel and erect towards the ostiole, or is spread 
over a larger, sometimes over the largest portion of the inner surface of the wall, 
and the asci then converge radially towards the middle line of the perithecium. 
Here too the asci and ascogenous organs alone form the ascus-portion of the 
perithecium; all the other parts belong to the envelope-apparatus; in structure 
therefore they are on a smaller scale than the envelope-apparatus and in their 
main features they are like cup-shaped apothecia. 
The wall is formed of a dense hyphal weft or pseudo-parenchyma, in Pleospora, 
according to Bauke, of actual parenchyma-like tissue. It is usually differentiated 
into a stronger often sclerosed outer layer, the thickness of which varies in the 
individual, and which can produce rhizoids and various other hair-structures on peri- 
thecia which stand detached on the mycelium, and an inner layer with delicate and 
‘often large cells. In some perithecia inserted in stromata, for instance in Tulasne’s 
Dothidea, in Claviceps, species of Cordyceps and Polystigma, this differentiation does 
not occur or it is not very distinct, and the wall is formed almost throughout 
of delicate cells. In its quite young state the wall is entirely closed round 
the initial organs of the ascus-apparatus and its ultimate investment, which latter 
will be described below. The ostiole is not formed till the development is more 
advanced, and it appears as an intercellular passage in the originally close 
tissue; it is partly schizogenetic by the separation of persistent tissue-elements 
in consequence of unequal growth, partly lysigenetic by the dissolution of a strip 
of tissue lying originally in the direction of the canal. The two processes seem to 
be often combined, and it is not easy to decide whether there is a solution of small 
strips of tissue along with the schizogenetic formation, or not. The ostioles in 
Sordaria, Melanospora, Claviceps, Epichloé, in Eutypa also according to Füisting', and 
Stictosphaeria are very largely schizogenetic; Füisting finds the lysigenetic formation 

1 Bot. Ztg. 1868, pp. 369, 641. 
