Carter. — Studies on the Chloroplasts of Desmids . /. 249 
with a starch-sheath, in several species numbers of small naked pyrenoids 
or granules of protein were observed in the superficial layers of the chroma- 
tophore. 
A. Summary of the Special Characters of Netrium 
and CLOSTERIUM. 
The chloroplast of Netrium consists of seven to twelve plates radiating 
from a central axis. 
The central axis of each chloroplast is occupied by a single long 
pyrenoid stretching throughout its whole length and surrounded by a thick 
sheath of starch which is almost invariably more than one layer of grains in 
thickness. 
Under certain conditions the pyreno-crystal of this long pyrenoid 
breaks up into numerous spherical or irregularly shaped portions which 
remain embedded in the central mass of starch grains. 
The only other genus in which these peculiar pyrenoids have been 
observed to occur extensively is Penium , although they are also general in 
the two species Cylindrocystis Brebissonii and Closterium Libellida. 
Lutman’s statement that the chloroplast in Closterium consists of 
a curved cone-shaped structure with relatively low ridges on its surface is 
not true for all species of this genus. 
The relative size of the axis and ridges varies with the species, and also 
to some extent within each individual species, according to the physiological 
condition of the cell. 
The pronounced undulation or anastomosis of the ridges frequently 
seen in certain species of the genus only occurs in individuals having fairly 
large ridges. Such individuals show a very irregularly branched structure 
in transverse section and are nearly always destitute of stroma-starch. 
Other individuals of these particular species containing much stroma- 
starch usually have a much broader axis and comparatively low ridges, 
which are seen in the front view to be practically parallel. 
Even in species swell as CL Lunula and Cl. Ehrenbergii , where the 
pyrenoids are arranged in the peripheral parts of the axis, there is consider- 
able variation in the relative size of the axis and ridges, often to be corre- 
lated with the variation in texture of the protoplasmic reticulum of the 
chloroplast, and therefore the relative position of the pyrenoids is also 
subject to a certain amount of variation. 
In spite of the fact that all species of Pleurotaenium are supposed to 
have parietal chloroplasts, it was observed that in PL Trabecida , var. rectum , 
the chloroplast consists of an axile rod, containing pyrenoids, with several 
low ridges projecting from its surface. 
