362 Harper.—Sexual Reproduction in Pyronema 
may have been due to the numerical inequality between the 
nuclei of the oogonium and antheridium, the lack in this case 
being on the part of the antheridium. They would then 
represent unfertilized egg-nuclei. It is evident they are 
incapable of further development since they are never found 
in the sub-hymenial layer of the ascogenous hyphae or in the 
young asci. In some cases they may be found in cells of 
the ascogenous hyphae as noted above, but never very far 
removed from the ascogonium. I am of the opinion as 
I have said that these are oogonial nuclei. It is, however, 
quite possible that they may be antheridial nuclei which 
found no egg-nuclei with which to fuse. This latter hypo¬ 
thesis would harmonize better perhaps with the general 
tendency in plants and animals to produce a larger number 
of male cells than of eggs. It was, however, noted above 
that in some cases a few nuclei were found in the antheridium 
after fertilization is complete and this has led me to assume 
that probably when an excess of male nuclei is present they 
are left in the antheridium. The chemotactic or other stimulus 
which leads the male nuclei to migrate through the tube 
to the oogonium would in this case be assumed to have 
exhausted itself when a number of the latter equal to the 
number of egg-nuclei had reached the oogonium. Whether 
these small and apparently unpaired nuclei found in the 
oogonium are male or female pronuclei, they do not develop 
further, and this fact is suggestive as to the necessity for 
fertilization and the impossibility of purely vegetative or 
parthenogenetic development on the part of the sexual nuclei 
in Pyronema. Ultimately these nuclei in the ascogonium 
become flattened upon its wall in an extremely thin layer of 
cytoplasm which is always found in it until a late stage of 
development. In the old fruits the nuclei and cytoplasm 
both are disorganized and appear as more or less scattered 
deeply stained granules. 
If we turn now to the development of the asci from 
the ascogenous hyphae of the sub-hymenial layer we shall 
And nothing essentially different from what I have already 
