Carter.— Studies on the Chloroplasts of Desmids. I. 243 
distinguished in stained material, and can be recognized in transverse 
sections (Figs. 65, 73, 83, 97, 99, and 10 1). It is only occasionally, when the 
chloroplast is feebly developed or when the chloroplast is very distended 
with stroma-starch, that the parietal plates are quite smooth. 
Most of the pyrenoids contained in the cell are embedded in the 
substance of the parietal plates. The number and size of the pyrenoids 
present vary considerably according to the condition of the individual cell. 
Eu . crassum and Eu. ventricosum seem to have the greatest number, seven 
or eight being scattered throughout each parietal plate, or in all about 
thirty to forty in each semi-cell (Figs. 82 and 100). In Eu. Didelta , Eu. 
oblongum , and Eu. ampullaceum there are about three in each parietal 
plate, most of them embedded in the thickest part of the chloroplast, where 
the radiating plates spread out to form the parietal plates (Figs. 65 and 97). 
Eu. affine has very few pyrenoids, only five to eight in each semi-cell, but 
these are very large (Fig. 93). Eu. sinuosum has about as many smaller 
ones (Fig. 62). 
Eu. cun eat uni. 
Eu. amentum , although agreeing essentially with Eu. crassum in the 
form of its chloroplast, differs from the general type in one or two respects. 
The central axis is usually in the form of a broad triangular plate, its surface 
parallel to the front faces of the semi-cell, as is frequently the case in 
Eu. Didelta. The two lateral edges of the plate are seen in transverse 
section to thicken abruptly and fork into two. Thus there are four masses 
of chloroplast, each extending towards the cell-wall, either as a parietal plate 
with projections on its external surface (Figs. 84 and 87) or as a more or 
less brush-like mass (Fig. 89 and 85). In the latter case the whole chloro- 
plast with the exception of the central axis is deeply cut into numerous long 
finger-like projections stretching towards the cell-wall, and definite parietal 
plates are not evident in the front view. Various stages between the 
comparatively smooth parietal plate and the brush-like form are to be 
found. 
Eu. cuneatum also differs from all other members of the group in the 
arrangement of its pyrenoids, of which there are three to twelve in each 
semi-cell. When there are comparatively few pyrenoids, these are embedded 
in the thickened edges of the central axis, all in one plane (cf. Fig. 85), but 
when there are more than can be accommodated in this position they spread 
outwards into the parietal masses (Fig. 87). They are, however, always 
found in the interior of the cell rather than in the parietal parts of the 
chloroplast. 
Occasionally Eu. cuneatum is found with a distinct parietal layer of 
chloroplast containing scattered pyrenoids, very similar to that of Eu. cras- 
sum, but more often it shows the structure described above. 
