Spore Formation in Derbesia 
BY 
BRADLEY MOORE DAVIS. 
With Plates I and II. 
HE genus Dei'besici described by Sober (’47) is chiefly remarkable 
JL for its zoospores. These are very large, and each is provided with 
a circle of numerous long cilia at its forward end. The general mor- 
phology of Derbesia is that of the Siphonales, with many points of 
resemblance to Bryopsis , except that the filaments are sparingly and ir- 
regularly branched. The zoospores of the Siphonales, however, are biciliate, 
Vaiicheria excepted, and small. The peculiarities of the zoospores of 
Derbesia have led Blackman and Tansley (’02) to suggest that its 
affinities are widely different from Bryopsis , a point which will be con- 
sidered later in the paper. 
The zoospores of Derbesia offer, then, a very interesting subject for 
cytological study, since their large size and the peculiar arrangement of 
the cilia give promise of interesting details in the form and development 
of the blepharoplast. This interest is further enhanced by Berthold’s 
account of their development. The zoospores are almost invariably 
uninucleate at maturity, but they are developed in relatively small 
numbers in sporangia which contain many thousands of nuclei when 
they are first formed from the parent filaments. Berthold (’81) reported 
that the larger nuclei, finally present one in each zoospore, are formed 
by the successive fusions of the very numerous nuclei within the spor- 
angium. This is, I think, the last account of nuclear fusions of this 
character which has not been disproved by detailed cytological investiga- 
tion, for similar accounts of nuclear fusions during oogenesis in the 
Saprolegniales, Peronosporales, and Vaucheria have been shown by later 
research to be incorrect, and such reductions in the number of nuclei 
within multinucleate reproductive cells have proved to be due in every 
case to nuclear degeneration rather than to nuclear fusions. 
[Annals of Botany, Vol. XXII. No. LXXXV. January, 1908.] 
