230 Carter.— -Studies on the Chloroplasts of Desmids. I. 
relative position of the pyrenoids has also been noticed in Cl. Elirenbergii , 
although it is not mentioned by Lutman (1910). 
The number of ridges arranged round the central axis is fairly constant 
for each species, Cl. striolatum having twelve or thirteen, Cl. angustahim 
nine or ten, and so on. 
The edges of the ridges are only ornamented to any great extent in 
Cl. Lunula. In this species they are hollowed out at intervals, or regularly 
lobed throughout their whole length, and these lobes or projections stretch 
out towards the cell-wall (Figs. 1 and 3 ). The edges of the ridges in 
Cl. Libelhda are usually conspicuously sharp and straight. 
The size of the ridges, as has already been stated, is a very variable 
character, and in certain species this variability may greatly influence the 
external appearance of the individual. In many cases the ridges when 
examined from the exterior are apparent as nearly parallel dark lines 
stretching from the region of the nucleus to the apices of the cell. This is 
usually the case in Cl. Libelhda (Fig. 8 ). In certain individuals, however, 
particularly of the species CL costatum , Cl. striolatum , Cl. regtdare , and 
Cl. angustatum , the ridges seem to travel in tortuous paths from end to end 
of the cell, and sometimes appear to lose their individuality by apparently 
fusing for a short distance one with another (Figs. 31 and 38 ). Although 
this is a very common occurrence in all the four above-mentioned species, it 
is by no means a constant feature of any one of them, individuals having 
ordinary straight ridges being also sometimes met with. Thus in some 
individuals of these species the ridges may appear to undulate very gently, 
and in extreme cases each individual ridge may bend alternately to the 
left and to the right in such a way as to produce a reticulation something 
like adioneycomb, or more irregular anastomosis against the interior of the 
cell-wall. 
This irregular arrangement of the ridges has been figured by Delponte 
(1873) in CL didymotocum } and also in two other species described by him 
as CL hirndo 2 and Cl. crassnm . 3 In the case of the first species at any rate 
he described the chloroplast as consisting of tortuous strings and tubules 
immersed in the protoplasm, and seemed very uncertain about the existence 
in this species of a chloroplast consisting of lamellae radiating from the 
centre to the periphery. Although Cl. didymotocum was not examined 
during this investigation, there seems to be no doubt that the appearance 
figured by Delponte was due to the same anastomosing of the ridges as has 
been observed in CL costatum , &c., in which species it has been definitely 
proved that the superficial tortuous ribbons such as were described by him 
for Cl. didymotocum are really joined up to the axis of the chloroplast in the 
interior of the cell, and are not merely isolated strings, as he seemed to think. 
1 Delp , 1 . 6 ., Tav. XVII, Figs. 32-4. 2 Delp., l.c., Tav. XVIII, Fig. 7. 
3 Delp., l.c., Tav. XVIII, Fig. 23. 
