Carter . — Studies on the Chloroplasts of Desnnds. III. 279 
each semi-cell, this particular form may be a distinct variety of C. praemorsum. 
At any rate it is interesting to note that two different kinds of chloroplast 
structure may sometimes occur in the same species. 
The remaining five species of Cosmarium examined were provided with 
parietal chloroplasts, which lie against or near the surface of the cell-wall. 
In C. Brebissonii the disposition of the chloroplasts is not always distinctly 
Text-fig. 2. A and b, C. formosulum, Iioff: a, Iront view ; b, optical transverse section. 
C-F, C. praemorsum , Breb. : c, front view ; d, end view ; E and F, showing irregularities in the 
number of pyrenoids. g and H, C. Turpinii , Br6b„ : G, front view, upper semi-cell in optical section ; 
h, optical transverse section. All x 810. 
parietal owing to the irregular distending of the chloroplasts in all directions 
by the large and numerous pyrenoids (Figs. 75-81). The number of chloro- 
plasts is often four, but they are subject to variation, especially in C. Brebis- 
sonii (Figs. 75-81), whilst in size and number the pyrenoids also vary con- 
siderably, often becoming very numerous in the larger species (Figs. 82-5). 
This variation in number of the chloroplasts and pyrenoids is general with 
parietal chloroplasts. 
Projections on the surface of the parietal expansions of chloroplast such 
as were described by LiitkemuUer (1893) in C. tessellation, &c., have been 
observed in the chloroplasts of four of the five species examined having 
parietal chloroplasts. 
