Carter. — Studies on the Chtoroptasts of Desmids. /. 239 
Group I. 
This group comprises in general the smallest species of the genus. 
The chloroplast consists of a fairly massive central portion containing 
one or more pyrenoids, and from this radiate towards the periphery various 
plates which are always destitute of pyrenoids. 1 The most important part 
of the chloroplast in these smaller species is the central axile mass, the 
peripheral parts being relatively small and insignificant. 
Eu. dubium , Eu. elegans , and Eu. binale. 
These small species, and probably all the smallest species of the genus, 
have a very simple type of chloroplast. Here there is a rather massive 
chloroplast which occupies practically the whole of the tiny semi-cell, and 
consists simply of an axile mass containing typically one pyrenoid, from 
which four lobes are given off, two of these enveloping each front wall 
of the semi-cell (Figs. 56- 8). Sometimes in the front view two ridges are 
visible in the median region, owing to the slight branching of the four 
primary lobes, but this is seen much better in the end view ; cf. Fig. 58. 
Eu. bident atum . 
Eu. bidentatum has a chloroplast which is rather different from that of 
any of the above-mentioned species. It sometimes has a more or less 
definite parietal layer of chloroplast, comparable to some extent with the 
parietal plates found in the larger species of the genus. The parietal 
portion, however, usually takes the form of irregular bands lying against the 
cell-wall (Fig. 51) ; it is only very rarely that definite parietal plates are 
present (Fig. 50). These bands are seen in the end view to be connected 
up to a central axile mass containing a single pyrenoid. They are, in fact, 
merely the flattened edges of the various lobes arising from the central axis 
(Fig. 53). There are usually four such lobes, but occasionally extra ones 
are present. 
Eu. pectinatum and Eu. ansatum . 
These two species, in spite of their fairly large size, have typically one 
pyrenoid in each semi-cell, but their chloroplasts, although being exactly of 
the same type as that found in the smallest species of the genus, are rather 
more elaborate. 
There is, in these two species, a single pyrenoid embedded in a central 
mass of chloroplast, which occupies comparatively less space than the 
corresponding axis of the smaller species, whilst the ridges are in conse- 
1 In one specimen of Eu. pectinatum a number of small naked pyrenoids or proteid granules 
were observed in the peripheral parts of the chloroplasts, but in this group ordinary pyrenoids 
never occur except in axile part of the chromatophore. 
