1904] DAVIS—OOGEN ESIS IN VAUCHERIA 85 
and d from within an oogonium. It will be seen.that a, 6, and c 
are nuclei which, although small (magnified 2,000 diameters), pre- 
sent the structure of the nuclei of higher plants; that is, each has a 
nucleolus lying among granules of a chromatic nature and linin. In 
c these structures are less conspicuous than in 6, while d shows 
unmistakable signs of degeneration, for its nuclear membrane appears 
very faint and there is scarcely any trace of chromatin or linin. The 
nucleolus, however, is generally large and stains deeply and is always 
the last structure in the nucleus to disappear. Figs. 6 and 7 show 
degenerating nuclei in oogonia shortly after the formation of the 
cross wall. 
It is very difficult to trace the degeneration and final dissolution 
of the numerous nuclei in the oogonia, because we are dealing with 
structures that become more and more difficult to stain and find. 
It becomes in the end impossible after the nuclear membrane dis- 
appears and the nucleolar material is scattered throughout the 
cytoplasm. These baffling conditions are identical with those in the 
oogonium of Saprolegnia which the author has recently described 
(DAVIS ’03, p. 239). 
The mature oogonia are finally uninucleate. There seems to be no 
doubt of this condition, and the factors governing the selection and 
survival of the fortunate nuclei are of interest. We know that the 
process in Saprolegnia (DAVIS ’03, p. 239-243) is intimately connected 
with the presence of organized structures in the protoplasm, the 
coenocentra, which are probably the morphological expression of 
dynamic centers. I have not been able to find a coenocentrum in 
Vaucheria. It is possible that the plastids might obscure such a 
structure, but this is not likely unless it were very small. But there 
are conditions around the surviving nucleus in the oogonium which 
closely resemble those of the Saprolegniales and Peronosporales. 
Before the formation of the cross wall the protoplasm in the oogo- 
nium is arranged quite irregularly. There is always the rather thick 
peripheral layer just inside the cell wall, but the interior region 
generally contains several irregular vacuoles which frequently open 
into one another. These conditions are partially shown in figs. 3-5, 
but of course they can be understood only by the examination of a 
number of consecutive sections. 
