366 Harper.—■Sexual Reproduction in Pyronema 
ment of forms like Pyronema , which have become familiar 
through their use as types in the text-books, I shall give 
a description of the main stages in the development of the 
ascus and the ascospores. 
In the young ascus the protoplasm is rather evenly dis¬ 
tributed, and the nucleus lies a little above the middle point 
of the long axis (Fig. 23). As the ascus increases in size 
a special denser mass of protoplasm, which is to form the 
spores, is differentiated in its upper portion. In the mature 
ascus this denser protoplasm is bounded above and below by 
a concave surface, and the remainder of the ascus is filled 
by a very vacuolar foamy protoplasm (Figs. 39, 40). The 
nucleus lies at first near the base of this denser mass. It is 
a large conspicuous structure with a single bright red-stained 
nucleolus and an irregular chromatin net. Fig. 35 shows 
an equatorial plate stage of the division of this nucleus. It 
is to be noted that this primary nucleus does not tend to 
occupy the centre of the dense protoplasm in which it lies. 
The two secondary nuclei into which it divides are also not 
arranged symmetrically as they are in the ascus of Lachnea 
for example. In Pyronema these two nuclei generally lie 
close together in a line which cuts the long axis of the ascus 
at a considerable angle. They remain in this relative posi¬ 
tion while dividing. Figs. 37, 38 show equatorial plate and 
dispirem stages of this second division. The daughter nuclei 
are still connected by the remnants of the spindle-fibres which 
have been drawn out into a narrow strand in Fig. 38. In 
this figure two nucleoli appear in the cytoplasm in the position 
of the nuclei before their membranes were broken down. 
The four nuclei resulting from the second division become 
arranged in a symmetrical row in the long axis of the ascus 
(Fig. 39). The spindles of the third division lie more or less 
transversely, so that the eight daughter nuclei formed are at 
first in an irregular double row, all of them within the mass 
of denser cytoplasm. 
The daughter nuclei of the eight-nucleated stage as in 
Lachnea are completely reconstructed before the beaks are 
