240 Carter. — Studies on the Chloroplasts of Desmids. /. 
quence much larger and more important. Four main ridges are given off 
from the central axis (Fig. 68), and as a rule each of these soon forks into 
two, sending one branch to the front wall and the other to the side wall 
(Fig. 61). Thus there are usually eight ridges in all, two running towards 
each front wall, and two towards each side wall. In the front view the 
chloroplast often looks more complicated owing to the extraordinary bending 
or further branching of these eight ridges, or the presence of extra ridges 
arising from the central axis (Figs. 59 and 66). The subsidiary ridges 
arising by the further division of the eight main ridges are seen in the front 
view as short dark lines. It is usually only the main ones which extend all 
the way from the nucleus to the apex of the semi-cell. In these two species 
also the edges of the ridges lying against the cell-wall are frequently lobed. 
The single pyrenoid in the centre of the cell may be replaced in 
well-nourished specimens by a group of two to four, usually in a line, 
one above the other, or more rarely side by side in the central axis 
(Figs. 59 and 60). 
The general form of the chloroplast in all these smaller species having 
a central pyrenoid is very similar, the chromatophore simply becoming more 
elaborate with the increase in size of the cell. There is very little variation 
amongst the individuals of each particular species, and the only deviation 
from the type was observed in one or two specimens of Eu. bidentatum , the 
same condition being also noticed on other occasions in Eu. pectinatum and 
Eu. binale . These peculiar specimens contained two pyrenoids in each 
semi-cell, side by side, but widely separated from each other. Moreover 
each pyrenoid was embedded in the centre of a separate mass of chloro- 
plast. The semi-cell therefore contained two axile chloroplasts, each con- 
sisting of an axis containing a pyrenoid and several radiating plates 
stretching towards the cell- wall ; cf. Figs. 54, 55, 70, and 71. It was 
interesting to notice this variation in the structure of the chloroplast, 
because in Eu. verrucosum (Figs. 90, 91, and 92) the chloroplast is normally 
of this particular type. It would be unwise, however, to attach too much 
importance to the coincidence, since the variation only concerned a few 
isolated specimens, and moreover the same kind of structure has also 
occasionally been observed in certain species of other genera, e. g. Cos- 
mar ium y which normally have a single chloroplast with one pyrenoid. 
Group II. 
The chloroplasts of species belonging to this group are characterized 
by the fact that the axile part is very thin and delicate, and contains few or 
no pyrenoids, whilst the cell-wall is covered with a thick parietal layer 
of chloroplast which is much more important and usually contains numbers 
of pyrenoids. 
