Carter.— Studies on the Chloroplasts of Desmids. III. 271 
C. elegantissimum. 
This species seems to have a chloroplast which is quite similar in all 
essential points to that of C. cucurhita, although it was described -by 
Lundell ( 1871 ) as having its chloroplasts in the form of parietal bands, and 
was placed by him in the sub-genus Pleurotaeniopsis , together with other 
species having parietal chloroplasts. Only one specimen was encountered 
during this investigation, and this had a central pyrenoid in each semi-cell, 
the chloroplast forming an irregularly shaped mass round it, with several 
short outgrowths radiating towards the periphery in various directions 
Text-fig. i. a and b, Cosmarium cur turn, (Breb.) Ralfs: a, front view; b, end view. 
c-e, C. achondroides, West: c, front view of semi-cell ; D, typical optical transverse section; 
E, optical transverse section of another individual unusual in its pyrenoids. All x 810. 
(Figs. 12 and 13). The chloroplasts were undoubtedly axile, and it is 
possible that in individuals with better developed chromatophores more 
definite plates like those of Cosmarium cucurbita might be visible. Possibly 
Lundell mistook the edges of such plates lying against the cell-wall for 
parietal bands. 
C diplospontm. 
In this species the chloroplasts are rather different from those of any 
of the other species examined having cylindrical cells, being much more 
elaborate in their structure. There is a large pyrenoid in each semi-cell, 
embedded in an axile mass of chloroplast. Instead of a limited number of 
definite plates, numerous thin string-like strands radiate in all directions 
from the central mass towards the periphery (Fig. 21, lower semi-cell). On 
reaching the cell-wall the end of each ray becomes flattened and extends in 
T 
