Carter . — Studies on the Chloroplasts of Desmids . /. 221 
The most striking thing about the chloroplasts of the higher members 
of the Desmidiaceae is their complexity of form. It is very rarely that one 
finds straight outlines, or simple ridges ; on the other hand, the chloroplasts 
are usually most complicated structures, the margins of the plates of which 
they are composed being divided and subdivided, and the ridges often 
branched repeatedly; cf. Figs. 65 and 77. 
In many species which have greater or smaller parietal expanses of 
chloroplast, the main body of the chloroplast is often removed a short 
distance away from the cell-wall, and numerous short outgrowths of chloro- 
plast extend from it towards the periphery. Such outgrowths were first 
noticed by Lutkemuller ( 1903 ), being described by him for Cosmarium 
tessellatum } C. turgidum , and C. de Baryi. It is most probable, however, 
that the phenomenon is not confined to these species, but is quite general, 
occurring in most genera where parietal or partly parietal chloroplasts are 
to be found. It has been observed during the present investigation in other 
species of Cosmarium , in various species of Euastrum and Xanthidium (see 
Figs. 62, 72, 89, 100, and 113), and also in Pleurotaenium elephantinum , Cohn. 
On the other hand, these projections do not seem to be an absolutely 
constant feature of any species in which they may be observed, but probably 
depend to a considerable extent on the condition of the cell. They are often 
very conspicuous in individuals with massive chromatophores, being in such 
cases both numerous and of large size. In cells with feebly developed 
chloroplasts they are often altogether absent, and the parietal part of the 
chloroplast closely envelops the cell-walk In general it is in cells with 
much available chlorophyll-bearing material that the most elaborate chloro- 
plasts are to be found, not only with regard to these projections from the 
external surface of the parietal parts, but also in the branching of the ridges 
and the elegance of the lobing and toothing of the edges of the various 
plates. But even in specimens with well-developed chloroplasts, the delicate 
form of the chromatophore may be secondarily interfered with by the 
presence of large quantities of starch, as will be explained later. 
Usually in cells with feebly developed choroplasts the same general 
structure can be recognized as in the better developed specimen of the 
same species, except that all superfluous ornamentation is wanting. Some- 
times, however, a considerable difference in appearance may be presented 
by two specimens of the same species, one with well-developed chloroplasts, 
the other with very little photosynthetic material. This is very marked 
in Cosmarium Brebissonii , Menegh., where some individuals have such 
large chloroplasts that these penetrate every part of the cell, which is almost 
full of pyrenoids and chloroplasts, whilst other specimens contain so little 
chlorophyll-bearing material that the chloroplasts form merely a thin layer 
lining the cell-wall, the interior of the cell being quite free from them. 
1 Liitkemiiller described these three species under the generic name of Pleurotaeniopsis. 
