Carter.— Studies on the Chloroplasts of Desmids. III. 281 
surface (Fig. 75). Each chloroplast contains one to four pyrenoids, whilst 
its edges and external surface are usually covered with numerous tiny finger- 
like outgrowths which stretch towards the cell-wall (Figs. 75 and 76). 
These outgrowths do not appear to have any definite relations with the 
granules on the external surface of the cell- wall, and sometimes become 
extraordinarily large, taking the form of short ridges running longitudinally. 
Sometimes a small chloroplast arises near the nucleus and stretches 
upwards, hidden in the interior of the cell, finally emerging near the apex of 
the semi-cell to form a parietal mass (Figs. 75 and 76). In cases where the 
pyrenoids become very numerous they cause extreme distortion of the 
chloroplasts, spreading farther and farther into the interior of the cell until 
the chloroplasts of opposite sides meet, and a practically solid mass of pyre- 
noids and chloroplasts is formed (Fig. 80 and 81). 1 
C. cucumis. 
It was only possible to examine a few specimens of this species, and in 
all these there was a thin parietal layer of chloroplast covering the whole 
cell-wall in the form of a delicate reticulum. Occasionally a number of 
more or less distinct bands, running longitudinally, could be distinguished 
(Fig. 73), but it usually happened that the parietal film was quite evenly 
distributed, with only occasional irregular colourless spaces. The chloro- 
plast was in all cases closely adherent to the cell-wall, and the pyrenoids, 
which were about fourteen to twenty in number and very variable in size, 
were suspended at some little distance in the interior of the cell by a delicate 
network of chloroplast (Fig. 74). In the limited number of specimens 
examined this delicate structure was general, and in no case were projections 
present on the external surface of the chloroplast. It is possible, however, 
that, had other material been available, specimens having more massive 
chloroplasts might have been encountered, and perhaps in such individuals 
the tiny outgrowths observed in the other species of the genus having 
parietal chloroplasts might be present. 
C. contr over sunt. 
This species was originally described as having axile chloroplasts with 
two pyrenoids in each semi-cell. 2 Its chloroplasts are parietal, however, four 
being the usual number (Fig. 86). Occasionally there are only two chloro- 
plasts, one on each front face (Fig. 87), and possibly more than four may 
also sometimes occur. The chloroplast plates may be of some thickness 
and contain from one to five pyrenoids (Figs. 86-8). They are removed to 
1 The pyrenoids also similarly distend the chloroplasts in certain species of Xanthidium having 
parietal chloroplasts, and here, too, the pyrenoids of opposite faces of the semi-cell are sometimes 
nearly incontact. See Carter, N. : Studies on the Chloroplasts of Desmids. I. Ann. Bot., vol. xxxiii, 
1919- 
2 Vide West, W. and G. S. (1904-11), vol. iv, p. 9. 
