2 82 Carter . — Studies on the Chloroplasts of Desmids. III. 
some little distance from the cell-wall, and their edges and external surfaces 
are covered with outgrowths which project towards the periphery, each 
projection corresponding to one of the granules on the cell-wall, as described 
by Liitkemuller (1893) for C. tessellatum (Figs. 86-8). 
C. ovale and C. Askenasyi. 
In these two species there are usually four parietal chloroplasts in each 
semi-cell, two on each front face (Fig. 82), although occasionally three may 
be present on one or other of the faces (Figs. 84 and 85). The main part ot 
each chloroplast consists of a thin layer removed to some little distance 
from the cell-wall, and containing from six to twelve pyrenoids. In both 
species there are numerous tongue-like projections stretching from the 
external surfaces of the plates towards the periphery, those of C. Askenasyi 
being rather more delicate and relatively more numerous than those of 
C. ovale (Figs. 82-5). 
Summary of the Special Characters of Cosmarium . 
Most of the species of Cosmarium examined have axile chloroplasts, 
although in a few the chloroplasts were parietal. In those species having 
axile chloroplasts there are either one or two chloroplasts in each semi-cell, 
and very often there is typically one pyrenoid in the axis of each 
chloroplast. 
The statement that all species of the genus having axile chloroplasts 
possess either one or two pyrenoids in a semi-cell is untrue, although there 
are many species which have either one or two points of pyrenoid formation. 
As in other genera of the Desmidiaceae, the actual number of pyrenoids 
present depends on the individual itself, and at any time a group of pyrenoids 
may be formed where originally there was only one. 
Many of the smaller species have a single chloroplast in each semi-cell 
consisting of a central axis, containing typically one pyrenoid, from which 
radiate either four more or less forked plates or a number of simple ridges 
or string-like outgrowths. 
In C. diplospornm there is a rough kind of parietal network arising from 
the lateral expansion of the ends of the chloroplast rays extending from the 
central axis. 
The plates arising from the central axis containing the central pyrenoid 
or group of pyrenoids are in C. pseudopyramidatum very complicated in form 
and irregular in arrangement. 
C. pyramidatum is similar to the previous species in the form and 
arrangement of its plates, but differs in its more delicate axis and in the 
arrangement of its pyrenoids, which, unlike those of C. pseudopyramidatum , 
rarely occupy the centre of the chloroplast. 
