272 Carter .—Studies on the Chloroplasts of Desmids. lilt 
a 
whole cell-wall is mantled by these irregularly shaped parietal masses, 
which form a rough kind of discontinuous network (Fig. 21, upper 
semi-cell). 
C. pyramidatum and C. pseudopyra m ida tu m . 
The chloroplasts of these two species greatly resemble each other, that 
of the smaller species, C. pseudopyr amidatum, being the simpler. In the 
latter species there is a massive axis occupying the centre of the semi-cell, 
and containing typically one pyrenoid, although sometimes two or more 
may be present (Figs. 22 and 23). The fact that the central pyrenoid 
sometimes divides to form a group in this species has been noted by 
Ducellier ( 1917 ), but, as has already been stated, this character is common 
to all species of the Desmidiaceae in which the points of pyrenoid formation 
are definite and fixed. From the lateral and apical edges of the axis there 
arise a large number of curved plates which are far more irregular in form 
than those of any other Desmid examined. In the front view their bent 
edges are seen stretching in various directions, but forming a single series 
which encircles the central pyrenoid or group of pyrenoids (Fig. 22), whilst 
in the end view they are seen to be arranged in four vertical lines (Fig. 23). 
The edges of the bent plates lying against the cell-wall are cut into finger- 
like projections which extend in various directions over its surface. 
C. pyramidatum (Fig. 24) has curved or bent plates which are exactly 
similar to those of C. psetidopyramidatum , the only differences between the 
chloroplasts of the two species being in the shape of the axis and the arrange- 
ment of the pyrenoids (Fig. 24). In the larger species there is a very thin 
plate, rather triangular in shape, in the middle of the semi-cell, and all 
round the edges of this the bent plates arise, travelling towards the front 
faces of the semi-cell (Fig. 24). In the end view, as before, they are seen 
to be arranged in four main series (Fig. 27). The, pyrenoids are very 
variable in number (2-14), and are arranged in a triangular or horseshoe- 
shaped series in the rather thicker part of the chloroplast where the bent 
plates arise from the thin axis (Figs. 24 and 25). Usually the pyrenoids all 
lie in one plane parallel to the front faces of the semi-cell (Fig. 25), but 
when they are very numerous they seem to separate into two different 
planes in the bases of the plates themselves (Figs. 26 and 27). Perhaps the 
most common number of pyrenoids is three, arranged one at each corner of 
the triangular axile plate (Fig. 24), but, as was noticed by Lutkemilller 
( 1893 ) and Ducellier ( 1917 ), they are very variable. Occasionally only one 
pyrenoid is present in the central position, as is the case with C. pseudo- 
pyr amidatum, but such cases are rare, the axis in the middle of the cell being 
usually far too thin for the accommodation of pyrenoids. 
Liitkemuller stated that when three or more pyrenoids are present in 
C. pyramidattnn it very often happens that a rounded hole appears in the 
parietal manner over its surface, forming an irregularly lobed mass. The 
