Carter . — Studies on the Chlor op lasts of Desmids . I. 235 
from the axis to the cell-wall in rather obscure longitudinal rows. Very 
often such a structure of the chloroplast is visible at the apices of the cell 
only, whilst in the broader part the ridges are more obvious. 
Cl. lanceolatum and Cl. Siliqua . 
These two species also have chloroplasts, consisting of a rather broad 
central axis, from the surface of which the ridges do not project very far 
(Figs. 6-7 and 45-6). In the external view the ridges are seen to travel in 
nearly parallel straight lines (Figs. 6 and 45), and although in Cl. lanceo- 
latum they may undulate very slightly, they never anastomose. In the 
latter species the ridges are about twelve in number, whilst in CL Siliqua 
there are about ten or eleven. The pyrenoids lie in a single line in the 
middle of the cell in both cases, and in Cl. lanceolatum they are often 
provided with a very thick starch-sheath, so that when they occur in 
a transverse section they occupy the whole of the broad axis (Fig. 7). 
CL costatum , CL striolatum , Cl. regiriare , and Cl. angustaturn. 
In these species there is great variation in the relative size of the axis 
and ridges ; in the external view, anastomosis of the ridges is consequently 
often seen (Figs. 31 and 38), whilst in other individuals they are nearly 
parallel and straight. Similarly this variation in structure is also evident 
when various transverse sections are examined, some sections showing 
a structure similar to that figured by Lutman, whilst in others the ridges 
may be very irregularly branched, according as they are straight or 
anastomose respectively (Figs. 26—30, 32-4, and 40-3). In extreme 
cases the axis may not have a definite rod- or cone-like form, but may 
merely consist of an irregular strand very much distended at the points 
where pyrenoids occur. Cl. costatum has usually thirteen or fourteen ridges, 
CL striolatum about thirteen, Cl. regidare twelve, and Cl. angustaturn about 
ten. The pyrenoids occur in a single row in the middle of the cell, occa- 
sionally spreading when very numerous towards the periphery (Fig. 34). 
In these species the difference in appearance of the .protoplasmic network 
of the chloroplast, and the difference in the relative size of the axis and 
ridges, according as much or little stroma-starch is present, is particularly 
noticeable. 
Cl. attenuatum . 
In the case of CL attenuatum the ridges are about ten in number and 
are seen in transverse section to be fairly large and plate-like (Figs. 11 and 
1 2). They were never observed to anastomose, but it is quite possible that 
in certain circumstances they would do so. The pyrenoids are in a single 
line in the middle of the cell (Fig. 10). 
