280 Carter. — Studies on the Chloroplasts of Desmids . III. 
C. Brebissonii . 
This species has most peculiar and variable chloroplasts which are quite 
different from those of any other species examined, and it is difficult to 
decide whether they should be considered axile or parietal. The general 
appearance varies considerably according as the chloroplast is massive or 
only very feebly developed, and its disposition apparently depends on this 
as well (Figs. 75-81). In specimens which have only feebly developed 
chloroplasts these take the form of thin parietal bands with small embedded 
pyrenoids (Fig. 78). The number of chloroplasts is about four, but is 
variable, and they are in close connexion with the nucleus at the base of 
the semi-cell, whilst their lateral margins are variously lobed or toothed. 
Sometimes the parietal bands are connected together in various ways by 
means of thread-like strands traversing the interior of the cell (Fig. 77). 
Specimens having this structure are comparatively rare. 
In the majority of cases the chloroplasts are more massive and are 
removed to some little distance from the cell-wall. In a transverse section 
many specimens show a peripheral series of about five chloroplasts just 
within the cell-wall, each containing one or more pyrenoids which project 
inwards towards the centre of the cell, whilst the thin film of chloroplast 
surrounding them sends out numerous finger-like outgrowths towards the 
cell-wall (Fig. 79). In such cases, the chloroplasts, although projecting 
a fair distance into the interior of the cell, can scarcely be called axile. 
Finally, in specimens having very massive chloroplasts, a transverse 
section shows an irregular central mass of pyrenoids surrounded by a thin 
film of chloroplast, which towards the periphery seems to associate itself into 
several more or less distinct lobes which send out long finger-like pro- 
jections to the cell- wall (Figs. 80 and 81). From the exterior such 
individuals are extremely dense and the nature of their contents cannot be 
elucidated. The pressure of one lobe of the chloroplast against its neighbour 
causes the formation of several longitudinal ridges, and this is all that can be 
distinguished in whole specimens. 
Although the chloroplast of such specimens seems to be intact and 
solid in the middle of the semi-cell, towards the apex and base the lobes 
seem to become more distinct and free from each other, and here the 
chloroplast is more definitely parietal. Besides this, it often happens that 
in transverse section one lobe is seen to be quite free from the remaining 
solid mass of chloroplast and pyrenoids (Fig. 81). 
Taking into account all these points it seems wiser to consider that the 
chloroplast of C. Brebissonii consists of four to seven parietal parts. Each 
part begins as a thin strand near the nucleus and proceeds towards the 
apex of the semi-cell, spreading out laterally just beneath the cell-wall so as 
to screen, by the united efforts of all the chloroplasts, practically the whole 
