278 Carter— Studies on the Chloroplasts of Desmids. Ill . 
In the case of C. biretum it was quite impossible to trace the parietal 
spreading of the ends of the chloroplast strands owing to the dense staining 
of the cell-wall itself, the chloroplasts being investigated entirely from 
sections (Figs. 64-6). 
The pyrenoids of C. reniforme show a marked tendency to multiply, as 
many as three being commonly packed together in the axis of a single 
chloroplast (Fig. 69), whilst in several individuals of this species the small 
pyrenoids or proteid granules so common in C. oclithodes were also observed 
in the parietal parts of the chloroplast (Fig. 70). 
C. praemorsiwi. 
Examples of this species from Dartmoor were found to have chloroplasts 
almost exactly similar to those of C. formosulum, there being two axile 
chloroplasts in a semi-cell, each with a single pvrenoid. There was very 
little attempt at the formation of parietal films of chloroplast (Figs. 50 
and 51). 
Later, a collection of algae from a tank in the Botanical Department of 
the University of Bangor was provided by Dr. Acton, which contained, 
amongst others, two forms of Cosmarium , which, although differing slightly 
from each other, are both to be referred to the species C. praemorsum . 
The smaller of the two was typical C. praemorsum , and, like the other 
examples previously examined, contained two chloroplasts in each semi-cell. 
The other form was slightly larger, and differed from the first in its slightly 
projecting apices, whilst its chloroplasts were quite different (Text-fig. 2, C, 
E, and F). Here there was only one chloroplast in each semi-cell, consisting 
of an axis containing typically one pyrenoid, and several plates radiating 
towards the periphery (Text-fig. 2, C and d). The axis of the chloroplast 
was often shortened in the apical region of the semi-cell (Text-fig. 2, c). 
A conspicuous character of this form was the unusual way in which the 
division of the central pyrenoid affects the chloroplast. Sometimes an 
individual was encountered having a compact group of two , or three 
pyrenoids in the centre of the semi-cell, as one would naturally expect (Text- 
fig. 2, E). But frequently there was a tendency for the two pyrenoids 
resulting from the division of the original one to separate from each other, 
and also for the chloroplast itself to constrict into two halves at the same 
time (Text-fig. 2, F). The union of the two parts of the chloroplast was 
always retained, however, even if only by means of a thin string-like strand 
connecting the two pyrenoids (Text-fig. 2, F, lower semi-cell). Sometimes 
even the starch-grains in the starch-sheaths of the pyrenoids were distorted 
by the pulling apart of the two halves of the chloroplast. Two separate 
chloroplasts were never observed, however, and so these variations in the 
form of the chloroplast are very difficult to explain. Because of the slightly 
different shape of the cell, and the fact that there is only one chloroplast in 
