Carter . — Studies on the Chloroplasts of Desmids . II. 299 
there may be thirty fairly large pyrenoids, or as many as eighty to a 
hundred rather smaller ones. 
It is in those species having compressed cells and a simple axile 
chloroplast plate that the pyrenoids are most numerous, and here they are 
scattered indiscriminately. In the thick-celled species, where the ridges 
of the, chloroplast have become relatively more important, the pyrenoids 
are reduced in number, and are more or less confined to those parts of the 
axis which give rise to the ridges (Fig. 27), whilst in those species having 
branched ridges they may be found also in the more peripheral parts of the 
ridges at the points of branching (Figs. 21 and 22). 
M. conferta . 
This species has a rather simpler chloroplast than any other species 
examined. Only one specimen was available for examination, and this had 
in each semi-cell a simple axile plate of very irregular shape. Ridges were 
only very slightly developed, and were found only along a few, not all, of 
the larger incisions. The pyrenoids were eight or nine in, number; they 
were variable in size and scattered irregularly (Fig. 1). 
M. dentictdata and M. Thomasiana . 
The chloroplasts of these two species greatly resemble each other. 
There is a large axile plate which is usually provided with a series of more 
or less distinct, though comparatively small, ridges following the outlines 
of the more important incisions between the lobes (Figs. 2-8). The 
prominence of the ridges, however, varies considerably with different 
individuals. This variation is again to be correlated with the amount of 
stroma starch present in the individual. If little starch be present, then 
the ridges along the incisions of the cell will usually be very distinct, 
whereas, if the chloroplast becomes very distended with stroma starch, the 
axile plate is often swollen to three or four times its former thickness and 
the ridges are lost. 
In M. Thomasiana the ridges parallel to the sinus project for some 
distance into the two outgrowths of the cell-wall at the base of the semi- 
cell ; the third or median lobule was not strongly developed in the material 
examined. 
In both species the pyrenoids are very numerous, there being usually 
about sixteen to seventy in M. Thomasiana , and twenty to forty in the case 
of M. dentictdata (Fig. 2). . Occasionally in the latter species there may 
be more than a hundred pyrenoids in a single chloroplast. 
M. papillifera. 
In this species there is a series of very distinct ridges arranged all 
round the incisions of the axile plate (Fig. 24). They are fairly large, very 
Z 
