Dimorphococcus Fritschii, a New Colonial Protophyte 
from Ceylon. 
W. B. CROW. 
With one Figure in the Text. 
HE genus Dimorphococcus , A. Br., has hitherto been known to be 
J- represented by two species of colonial Isokontae : D. lunatics , A. Br., 
and D. cordatus , Wolle. These organisms are remarkable in their method 
of colony formation, the four cells that are produced by division in each 
parent cell remaining attached for some time in groups by the agency of the 
parent cell membrane, which, at least in the older state, takes the form 
of connecting threads of mucilage. Dimorphococcus shares this type of 
colony formation with the genera Westella, De Wildemann, Dictyosphaerium, 
Ehrenb., and Radiococcus , Schmidle. Hence some authorities consider these 
to form a special family among the unicellular Isokontae : the Dictyo- 
sphaericeae (5). But Dimorphococcus is distinguished from these related 
types in a character which gives the genus its name, viz. the dimorphism of 
its cells. 
Whilst examining specimens of plankton organisms in a collection from 
the inland fresh waters of Ceylon, made by Prof, F. E. Fritsch in 1903 and 
preserved in dilute formalin, I met with some colonies of a colonial proto¬ 
phyte which showed cells with a rich starch content and massive parietal 
chloroplast. The colony formation, moreover, was of the type mentioned 
above, and the dimorphism of the cells was very obvious. The organism 
thus had the essential characters of the genus Dimorphococcus , but further 
investigations showed that it differed from the two species mentioned 
above. 
The colonies occurred in considerable quantities in the following 
localities: Tank 1 Borlasgama, near Colombo, 8th November; tank at 
Kekunadure, about five miles from Matara, 8th September ; canal leading 
from river to lake, near Bentottle, 6th September ; Lake Madampe at 
Ambalangodda, near the sea, 13th September; lake at Panadure, 16th 
September. The organism was not found in collections from several smaller 
1 The 1 tanks ’ in Ceylon are reservoirs of partially artificial origin. In them, however, the 
micro-organisms live under normal conditions. 
o 
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[Annals of Botany, Vol. XXXVII. No. CXLV. January, 1923.] 
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