NOTE ON THE CYTOLOGY OF CALOTHEIX FESCA. 623 
Note on the Cytology of Calothrix fusca. 
By 
Dr. !V. H. 8wclleng;rel>el, 
Amsterdam. 
With Plate 32. 
While studying the cytolog}' of several TrichohacterinEe I 
came across a representative of the group of Cyanophyceae, the 
study of which may cast perhaps some light on the question 
of relationship between Cyanophycese and Bacteria. 
I found Calothrix fusca in aquaria among large quanti- 
ties of Gloeocapsa ; I never found it not associated with those 
algse. It seems not impossible that a symbiotic relationship 
exists between those two algae, a relationship which would be 
obviously beneficial to Calothrix, this species being more or 
less deprived of chlorophyll. This question, however, must 
remain for the Avhile a mere hypothesis, because I was not 
able to study the question more thoroughly. 
'I'he dimensions of the cells are very variable. At the end 
of the cell-filaments the cells are rather short (from 3‘6 ju — 
7‘2ju), but lengthen towards the base (from 7'8 /j — 10'8^); 
their breadth is from 8-6 fi— 7-2 fi. The filaments which are 
enclosed in thick hyaline sheaths are pseudo-ramified. Each 
pseudo-ramification possesses at its base a heterocyst and 
some concave cells. 
To study the cytological details the cell -filaments were 
fixed in Pfeiffer’s solution, washed in alcohol 60 per cent., 
after the ordinary passages through alcohol embedded in 
