Nuclear and Cell Division in Dictyota 
dichotoma. 
BY 
DAVID M. MOTTIER, 
Professor of Botany in the Indiana University . 
With Plate XI. 
"VtONG the .Brown Algae certain representatives, as 
D\. Fuchs, Stypocaulon , Sphaceleria , and Dictyota, have, in 
recent years, been found to afford favourable material for 
the investigations of cytologists dealing with nuclear and 
cell-division. One of these genera, Stypocaulon (Swingle, ’97), 
was the first Alga in which the persistence of the centrosome 
was, without doubt, demonstrated throughout successive 
generations of vegetative cells. The discovery, in 1897, of 
motile antherozoids in Dictyota and Taonia by Williams (’97) 
has aroused a renewed interest in the Dictyotaceae from the 
standpoint of evolution, and my own observations will show, 
I think, that in the tetraspore mother-cells of this plant we 
have a rather favourable object for a study of the centro- 
sphere and the development of the karyokinetic spindle, as 
well as the formation of the cell-plate. 
A short sojourn at the Zoological Station in Naples, in 
the spring of 1898, enabled me to collect material and to 
make a preliminary study of the centrosphere, the results 
of which have already been published in the Berichte der 
[Annals of Botany, Vol. XIV, No. L 1 V. June, igoo.] 
