348 Harper.—Sexual Reproduction in Pyronema 
thickening of the walls around this pore. This thickening 
is quite conspicuous in sections and seems to be for the 
most part on the wall of the tube rather than on that of 
the antheridium. Figs. 9-13 show it extending back over 
a portion of the underwall of the beak. As a result of this 
thickening an extremely strong suture is formed between the 
antheridium and conjugating tube, so that they can be bent 
and turned up on each other as Kihlmann’s figures show 
without being pulled apart. Without doubt this extra rein¬ 
forcement of the walls at this point is necessary to withstand 
the strain which comes with the passage of the nuclei from the 
antheridium into the conjugating tube. The flow of nuclei 
from the relatively wide cavity of the antheridium through 
the narrow pore and beak of the conjugating tube must 
produce considerable strain on the walls of the latter, and the 
thick irregular ring-shaped thickening provides against the 
possibility of a rupture. While the pore has been forming, 
the centre of the lens-shaped receptive spot of the antheridium 
has become spongy and vacuolar (Figs. 11 - 12 ), and its 
especially fine granular structure gradually disappears. 
During the process of fusion just described the contents of 
the conjugation-tube have been undergoing a striking change. 
The protoplasm of the tube has finer meshes and stains less 
deeply than that of the oogonium. At its first maturity, 
before the pore is formed, its nuclei are much smaller than 
those in the oogonium. These nuclei now undergo degenera¬ 
tive changes of quite a characteristic type. Their chromatin 
content seems to be reduced and is distributed for the most 
part on the nuclear membrane. For a time the minute red- 
stained nucleoli become more conspicuous. The nuclei then 
swell and become extremely transparent (Fig. 6). They may 
also tend to flow together in groups in the axis of the tube. 
Finally they collapse or break down into dense strands or 
shreds which are frequently connected so as to form a coarse, 
much broken network in the protoplasm (Figs. 8-13). This 
network stains strongly with safranin and seems quite evenly 
distributed through the tube with the exception of the beak. 
