DEVELOPMENT OF THE PERITHECIUM OF MELIOLA. 
593 
filled with almost fluid contents, and partly from the extreme delicacy of the young 
asci, I have been unable to decide whether any distinct branching of the ascogenous 
cells precedes the formation of the definite asci ; probably such is the case. We 
have now followed the development of the perithecium to the period when it may 
' be considered ripe : a period of some duration, since the asci are continually and 
1 successively formed in the tuft for some time. 
Fortunate sections of the perithecium wall at this stage have yielded the following 
information. In the centre of the apical wall, where a slight protuberance sometimes 
occurs, the cells of the inner wall are found to radiate towards a pale translucent spot 
or pore (see Plate 42, fig. 36), and although I have not been able to obtain sections 
exactly through this, and am therefore unable to affirm positively that it is an actual 
pore, there seems little doubt that this is at least the weak point through which the 
spores escape from the ripe perithecium, no doubt forced through by the swelling 
of the materials around, Bob,net‘“ believes that the perithecium opens by a circular 
rupture at the base : I have tried to confirm this, but failed, and am strongly persuaded 
that the apical spot figured is the point of exit for the spores. That a minute pore 
should escape observation from without is not remarkable : the reflection of the light 
from the black shining outer cells might easily obscure it. The general structure of 
these walls has already been described, and fig. 34, drawn from an extremely for¬ 
tunate and very thin section, shows the details. 
The very young ascus presents no features of importance to distinguish it from that 
of many other pyrenomycetous fungi. In its earliest state it is recognisable as a 
single thin-walled, club-shaped cell, tapering to a point at the lower attached end, and 
filled with finely granular, yellowish protoplasm (see Plate 44, fig. 37, a.) : sometimes 
a small pale, refractive nucleus-like point is seen in the protoplasm. As the young 
ascus grows longer, and its protoplasm increases in quantity, a fine, sharp division line 
makes its appearance somewhat oblique to the long axis of the wdiole (fig. 37, c.) ; this 
is soon followed by a second, similar longitudinal division, in a plane at right angles to 
the former (fig. 37, d), and four well-defined masses are thus marked out. These, the 
young spores, do not include the whole of the protoplasm (fig. 37, d. and f ), but lie in 
a scanty matrix of granular matter, closely opposed face to face, and following the 
curve of the enlarging ascus wall on their outer walls. 
As the four, almost fusiform young spores increase in size, and acquire more distinct 
membranous envelopes, they come to lie somewhat more loosely in the cavity of the 
ascus, and may cross one another in accommodation to the space at disposal. Then 
appear cross-septa (fig. 37, e., /.), dividing the material of the spore into a number of 
compartments varying from three to five—or, in one case, a single septum only is 
formed—and vacuoles and granules appear in the hitherto almost homogeneous con¬ 
tents. As the spores ripen, their cross-septa become more firmly marked, their outer 
walls thicker, and, gradually brown or nearly black in colour, like the hyphae of the 
* Op. cit., p. 261. 
