Carter . — Studies on the Chloroplasts of Desmids. III. 277 
plates may previously fork before spreading out to form the parietal 
outgrowths, but probably part of the branching visible in the optical trans- 
verse section (Fig. 72) is only apparent, being due to the lateral extension of 
the outgrowths on both sides of the plate. The actual shape of the out- 
growths varies amongst individuals, and the extent of their development 
depends largely on the size of the chloroplast. In some individuals with 
slender chloroplasts the edges of the plates form merely a delicate network 
against the cell-wall, and the beautiful lobing so conspicuous in others is 
wanting. 
C. Turpinii , C. ochthodes , C. Botrytis , and C. tetraophthahnum . 
These species have chloroplasts which are very similar to each other 
The axis of each chloroplast gives rise to four to six plates which radiate 
towards the exterior (Figs. 40, 57, and Text-fig. 2, H), and the peripheral 
edges of these plates often spread out over the internal surface of the cell- 
wall to form extensive parietal films of chloroplast in the form of a delicate 
reticulum (Figs. 37, 45, 49, 56, Text-fig. 2, G). Very often practically the 
whole surface of the wall is thus mantled with a thin layer of photosynthetic 
matter, only small gaps being left. In C. ochthodes this parietal layer is 
often the seat of numerous tiny proteid granules, or naked pyrenoids 
(Figs. 37 and 49), and these have also been occasionally noticed in 
C. tetraophthahnum (Fig. 56). The ordinary large pyrenoids of the latter 
species show a particular tendency to multiply, and a group of two to four 
is commonly found embedded in the axis of one or more of its chloroplasts 
(Figs. 56 and 57). 
C. amoenum , C. subcucumis , C. reniforme, and C. biretum . 
In the chloroplasts of these species there are simple strands radiating 
from the axis rather than definite plates. The rather spherical mass of 
chloroplast containing the pyrenoid or group of pyrenoids sends out these 
projections towards the cell-wall in all directions, except towards the other 
chloroplast of the semi-cell (Figs. 62 and 70). One of these outgrowths 
usually connects up the axis of the chloroplast with the nucleus (Fig. 62). 
The chloroplast strands are very numerous, and may sometimes branch 
slightly (Figs. 64 and 66). On reaching the cell-wall they usually spread 
out to form irregularly shaped parietal masses lying against the cell- wall, 
forming a rough kind of network, which is, however, rather different from 
the more or less continuous parietal reticulum of C. ochthodes (Figs. 67 
and 69). 
The chloroplasts of the specimen of C. amoenum examined (Figs. 62 
and 63) were not sufficiently massive to show the formation of a parietal 
network, but it is quite likely that under favourable conditions it is also 
developed in this species. 
