Carter . — Studies on the Chlor op lasts of Desmids . I. 231 
In the case of specimens having nearly parallel or very slightly undu- 
lating ridges, these are seen in transverse section radiating from the central 
axis at practically equal distances from each other all the way round, and as 
a rule the ridges in such cases are very small in comparison with the size of 
the axis (Figs. 30 and 34). But where the undulation of the ridges becomes 
very pronounced, and their paths are very tortuous, transverse sections 
reveal a remarkable difference of structure. The axis here is usually very 
slender, and the ridges, instead of originating quite independently of each 
other from the axis, as in cases where they are nearly parallel, are seen in 
transverse section to show a certain amount of branching. Thus in the 
case of an individual of CL costatum , which would have had fourteen ridges 
visible from the exterior, a transverse section showed that the central axis 
gives off five ridges only, and that the fourteen ridges lying against the cell- 
wall are the ultimate products of the branching of these original five 
(Fig. 3a). Another specimen of the same species had thirteen ridges 
resulting from the subdivision of four primary ridges, and so on, the 
arrangement of the ridges round the axis varying with individuals. 
Again, the combination of the ridges at various points in the same cell 
differs continually, as the examination of consecutive sections shows. Thus 
Figs. 41-3 represent consecutive sections of a specimen of CL striolatum 
having thirteen ridges, and from a comparison of these the rapidly changing 
position and arrangement of the individual ridges in a short length of the 
cell is quite evident. The ridges, where they overlap the nucleus (Fig. 43), 
are quite free and distinct from each other, whilst in the remaining two 
sections the ridges are joined together in quite different combinations in 
each case. Thus it is clear that any particular ridge partially fuses for 
a greater or shorter distance with one or more neighbouring ridges, and, at 
various points in the length of the cell, any individual ridge is united with 
ever-varying groups of other ridges, being restricted of course to its own 
immediate neighbours. 
As seen in transverse section, however, the fusion of any two ridges 
rarely extends all the distance from the central axis to the, periphery, the 
ridges being quite free from each other as they lie against the cell-wall, but 
fusing in various combinations in the interior of the cell (Figs. 29, 32, and 41 ). 
Where, in the external view of an individual, two ridges come so close 
together as apparently to fuse, a careful examination will usually show that 
they are quite distinct from each other on the surface (Fig. 38), although 
they are probably united just beneath, as seen in the tangential section, 
Fig. 39. Sometimes, however, complete fusion of two ridges may occur 
near the apex of an individual, or one ridge may end abruptly, so that 
there may not be so many ridges round the axis near the apex of the cell 
as lower down. 
Thus, throughout the whole length of the cell the arrangement of the 
s 
