*7 
Davis. — Spore Formation in Derbesia. 
nuclear membrane. The larger nuclei become distributed rather uniformly 
throughout the sporangium, lying generally at some distance from one 
another. 
The smaller nuclei are found sometimes singly but more frequently in 
groups within areas of cytoplasm bordered by plastids. They never fuse 
with one another. These smaller nuclei gradually decrease in size, becoming 
much smaller than the plastids, and finally, losing their chromatin content, 
break down in the cytoplasm. They have generally disappeared com- 
pletely at the time the spores are formed, except for deeply-staining 
globules in the cytoplasm which are the remains of the nucleoli. 
The large surviving nuclei are not associated with cytoplasmic centres 
such as coenocentra, but the arrangement of the protoplasmic strands 
indicates that they are the paths of cytoplasmic streams passing to and 
fro between the nuclei and the cytoplasm. The large nuclei are, there- 
fore, probably themselves important centres of dynamic and metabolic 
activity. 
The segmentation of the protoplasm does not begin until the pro- 
cess of nuclear degeneration is practically ended. Cleavage begins at the 
periphery of the protoplast and the protoplasm is quickly cut by curved 
and branching furrows, that finally divide it into uninucleate masses, which 
are the zoospore-origins. Occasional binucleate spore-origins have been 
noted. The zoospore-origins round up and the plastids take a radiate 
arrangement around the centrally placed nucleus with its investing 
envelope of cytoplasm and radiating protoplasmic strands. 
The nucleus of the spore-origin then moves from the centre of the 
protoplast towards the periphery. Perhaps a third or a fourth of the 
protoplasmic strands on the side of the nucleus nearest the periphery become 
arranged in the form of a funnel. Granules may be found on these strands 
apparently moving outward towards the plasma membrane. 
These numerous granules accumulate in a circle just underneath the 
plasma membrane and fuse with one another to form a deeply-staining, 
firm ring, which is the blepharoplast. The strands connecting the nucleus 
with the developing blepharoplast apparently disappear after its develop- 
ment, and the nucleus passes back to the centre of the zoospore, the 
plastids becoming distributed about it again in a radiating arrangement. 
The blepharoplast then splits to form two rings, one slightly below the 
other, and the circle of cilia is developed from the lower ring. 
During the development of the zoospores the homogeneous chromatin 
body undergoes changes ; its material becomes granular or cloudy and 
strands appear, forming an irregular network of coiled threads, from which 
is developed the spirem of the first mitosis in the germinating spore. 
The two rings of the blepharoplast remain for some time closely 
pressed against the cell wall at the base of the germinating spore, but they 
c 
