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1904] DAVIS—OOGEN ESIS IN VAUCHERIA 83 
the enlargement is accompanied by a stretching of the cell wall, which 
is always much thinner about the young oogonium than around the 
stalk and vegetative filament, a fact which is clearly shown in figs. 
4, 5,6,and 7. The growth of the oogonium results from the accumu- 
lation of large amounts of protoplasm with numerous nuclei and 
chloroplasts, together with the formation of vacuoles which flow 
together, so that finally the protoplasm lies peripherally around a 
central space crossed by a few delicate strands and films of proto- 
plasm. 
The number of nuclei is variable, but always large; the range is 
probably from about 20 to 50. These nuclei are carried into the 
developing oogonium by the accumulation of protoplasm. They 
lie very close together at the tip of the young structure (fig. 1), but 
become scattered as growth proceeds, agreeing in this respect with 
the conditions found in all the growing points of Vaucheria. I have 
seen no indication of nuclear division in the oogonium, and am 
positive that it does not occur in stages as old or older than those 
shown in figs. 2 and 3. It is quite probable that mitotic figures are 
present in the vegetative branch before the development of the 
oogonia, but I have never seen the spindles. The nuclei are so very 
small and the plastids so numerous that studies of nuclear division 
in Vaucheria will be very difficult. It is important to note that there 
are no mitoses during the growth of the oogonium and none after 
its separation by the cross wall from the parent filament. In these 
respects oogenesis in Vaucheria is somewhat different from the pro- 
cesses as known in Saprolegnia and the Peronosporales, where there 
seem to be always one or two general mitoses after the oogonium is 
formed. The absence of nuclear divisions during oogenesis in 
Vaucheria presents serious difficulties for the theories of some authors 
that such mitoses indicate reduction phenomena in those fungi where 
they have been most studied. These speculations have been recently 
criticised by the writer (D&vis ’03, pp- 339-342) and the subject will 
be further considered later in this paper. 
We will now describe he development of the cross wall by which the 
oogonium is separated from the parent filament. It appears when the 
oogonium is about two-thirds its mature size. The wall is laid down 
between two plasma membranes, as was shown by HARPER (’99) for the 
