5 
Davis . — Spore Formation in Derbesia. 
nuclei in the oogonia of the Saprolegniales, Peronosporales, and Vaucheria 
(Davis, ’03, p. 341, and ’04). The physiological conditions within the 
oogonia of these groups and the sporangium of Derbesia are very similar. 
These reproductive organs are overstocked with nuclei in the beginning of 
their development, for reasons that are probably phylogenetic, and related to 
times when the organs developed many more reproductive cells than they 
do at present. After the reproductive organs are separated from the parent 
filaments the nuclei find themselves under conditions where there is not 
sufficient nourishment for all, and a struggle for existence develops with the 
subsequent degeneration of all the nuclei except the favoured few. 
In the Saprolegniales and Peronosporales the survival of certain nuclei 
is determined by their favourable position near those metabolic centres in 
the cytoplasm, the coenocentra. In Vaucheina (Davis, ’04) the surviving 
nucleus lies near the centre of the oogonium in an accumulation of cyto- 
plasm which is probably the region of the cell most favourable for nuclear 
metabolism. The sporangium of Derbesia is so large a coenocyte that its 
cytoplasm would not be expected to become uninucleate. However, regions 
become differentiated and dominated by certain nuclei which find there 
more favourable conditions for growth, and consequently obtain a lead over 
all others, finally forcing their degeneration. The positions of these 
favoured centres of metabolic activity are marked by the accumulation of 
granular cytoplasm around the large nuclei and the protoplasmic strands 
radiating out among the plastids. 
The last stages in the degeneration of the small nuclei are more easily 
followed in Derbesia than in Saprolegnia, Albugo, ox Vaucheria, because the 
nuclei are not so minute as in the latter forms. The nuclei decrease 
in size as shown in Fig. 10 until they are less than half the diameter of the 
plastids. The nucleolus still stains distinctly, but the chromatin body 
becomes faint and is finally quite lost, so that the nucleolus alone comes to 
lie in a vacuole which is the remains of the nuclear cavity. The boundary 
of the vacuole finally breaks down, and the nucleolus then passes into the 
cytoplasm as a deeply-staining globule. Fig. 11 shows a group of de- 
generating nuclei in a region of granular cytoplasm surrounded by plastids. 
This group is in an advanced state of degeneration. Some of the nuclei 
still have the nuclear membrane, but the globules lying freely in the cyto- 
plasm are from those that have become disorganized. These nucleoli 
fragment into smaller globules, which finally disappear. 
The Segmentation of the Protoplasm. 
The segmentation of the protoplasm does not begin until the process 
of nuclear degeneration is practically ended. Traces of the smaller nuclei 
may still be found, but they are very difficult to recognize. The sporangium 
then contains only the larger nuclei quite uniformly distributed through the 
