Studies on Nuclear Division in Desmids. 
I. Hyalotheca dissiliens (Sm.) Breb. 
BY 
ELIZABETH ACTON, M.Sc. 
With Plate VIII and four Figures in the Text. 
Introduction. 
T HE only account which has so far appeared of the division of the 
nucleus in Desmids is that by Lutman , 1 in which he describes 
the cell- and nuclear division in Closterium . 
It was therefore suggested by Professor G. S. West that this subject was 
a suitable one for investigation, and the present contribution is intended to 
be the first of a series of papers dealing with the nuclei and nuclear division 
of Desmids. 
The fact that very little is known of the cytology of Desmids is 
probably largely due to the difficulty of obtaining suitable material to work 
upon. It is by no means an easy matter to obtain a continual supply 
of any of the larger Desmids. They usually occur in places which are not 
easily accessible, and when brought indoors they cannot be kept for 
any length of time in a healthy condition. The ordinary culture-methods 
which serve for the common filamentous Algae are a complete failure as far 
as Desmids are concerned, and the conditions under which they divide 
or form zygospores seem to be so highly specialized that it has not been 
possible to determine them up to the present time. So that, while it 
is possible accidentally to discover Desmids in quantity in a dividing 
condition, the possibilities of finding them at any particular time or inducing 
them to divide by artificial means are rather remote . 2 
Hyalotheca dissiliens is the only Desmid I have been able to obtain, so 
far, in sufficient quantity to give complete results, and it is for this reason 
alone that it has been chosen for the initial paper. Unfortunately, the 
nucleus in Hyalotheca is too small to give entirely satisfactory results. 
No attempt will be made in this paper to compare the results obtained 
with those of Lutman or to discuss their bearing with regard to other Con- 
jugatae. I hope to complete shortly the investigation of several of the 
1 B. F. Lutman : Cell and Nuclear Division in Closterium. Bot. Gaz., 51, 1911. 
2 Some of the larger species of Closterium are an exception to this statement, as they will grow 
and multiply rapidly in large tanks in greenhouses, &c., and will also survive culture experiments. 
[Annals of Botany, Vol. XXX. No. CXIX. July, 1916 ] 
