236 Car ter .—Studies on the Chtoroplasts of Desmids. 1 \ 
CL Libellula. 
This species always seems to have fairly large ridges, even when quite 
a considerable amount of stroma-starch is present (Fig. 9). They are about 
twelve in number, and are occasionally seen to anastomose, although being 
as a rule quite straight (Fig. 8). The pyrenoids are in a single line in the 
middle of the cell, and are peculiar in being usually of very great length, 
a single pyrenoid sometimes stretching through more than half the entire 
length of the chloroplast (Fig. 8). Consequently they are very few in 
number, about two or three in each half-cell. Excepting that a single 
pyrenoid rarely stretches through the whole length of the chloroplast, these 
pyrenoids agree in every particular with those found in the genus Netrium 
(Figs. 13-19), being provided with several layers of starch-grains. This is 
the only species of Closterium in which such pyrenoids have been observed. 
In the three smaller species, Cl. Dianae , Cl. rostratum, and Cl.jnncidum , 
the ridges seem to be fairly large considering the small size of the cell 
(Figs. 21-5, 35-7, 47, and 48). Cl. Dianae and Cl. rostratum have about five 
or six ridges which sometimes undulate gently (Fig. 21), whilst in the case 
of Cl. juncidum they are about seven in number. 
Note : — The chloroplasts of Pleurotaenimn Trabecida , (Ehrenb.) Nag., 
var. rectum , (Delp.) W. and G. S. West. 
The chloroplasts in the genus Pleurotaenium are generally supposed to 
be in the form of parietal bands, with numerous pyrenoids embedded in 
them. In the case of PI. Trabecida, var. rectum , it was found, however, after 
the examination of a large quantity of material, that the chloroplast is 
invariably axile, with a single row of pyrenoids in the middle of the cell 
(Fig. 49). A few low longitudinal ridges, which are sometimes twisted 
slightly in a spiral round the axis, project from its surface. There was no 
suggestion in any individual of the chloroplasts being even partly parietal. 
V. The Chloroplasts of the Genus Tetmemorus. 
It has long been known that the chloroplasts in Tetmemorus are axile, 
with a central row of pyrenoids. This latter character was indicated in the 
figures of Ralfs ( 1848 ) for the three largest species of the genus, whilst 
de Bary ( 1858 ) also illustrated the ridged nature of the chloroplast in 
T. Brebissonii , but since these early times no work has been done on 
the chloroplasts of the genus. 
Three species were examined during this investigation, T. Brebissonii , 
(Menegh.) Ralfs, T. granulatus, (Breb.) Ralfs, and T. laevis , (Kutz.) Ralfs. 
All these species have axile chloroplasts, but whilst those of the two smaller 
ones resemble each other, the chloroplast of T. Brebissonii is rather 
different. 
