Carter . — Studies on the Chloroplasts of Desmids. /. 223 
In some species the form of the chloroplast varies very little amongst 
individuals, and a typical form can be described which is true in all 
essentials for practically all specimens, the only differences being minor 
ones, such as those due to external conditions, as mentioned above. This 
is the case with many species of Staurastrum and Cosmarimn . In other 
species there is a marked tendency to vary, and a considerable proportion 
of individuals do not conform to the type. This is very noticeable in the 
larger species o iEuastrum, where, although the typical form of the chloroplast 
is axile, all stages to the parietal condition are to be found ; cf. Figs. 72-5 
and 100-5. Liitkemuller ( 1893 ) noticed the existence of such variations 
in Cosmarium docidioides 1 and Xanthidium Brebissonii , 1 2 and possibly it 
also occurs in other species. The chloroplasts of the thicker-celled species 
of Micrasterias are also variable, but in quite a different way. 
The very intimate connexion between the nucleus and chloroplasts was 
noticed in many species. This is seen best where there are two axile 
chloroplasts in each semi-cell, as in certain species of Cosmarium. In such 
cases the basal part of each chloroplast is drawn out into a string-like 
portion, which is apparently attached directly to a corner of the nucleus, this 
being usually more or less rectangular in shape. Very often as a result of 
the frequent use of the centrifuge in the preparation of the material, the 
nucleus becomes displaced from its normal position in the isthmus, and is to 
be seen a little distance away in one of the semi-cells, dragging behind it the 
chloroplasts by means of their string-like attachments, the connexion 
between them still unbroken. Thus there must be a very vital connexion 
between the nucleus and chloroplasts, either directly or through the medium 
of the layers of protoplasm which surround them. In any case it must be 
very strong to withstand the treatment described above. 
Sometimes similar thread-like attachments are noticed between the 
edges of the chloroplast plates and the layers of cytoplasm lining the cell- 
wall. This seems to be very common with chloroplasts which are not 
sufficiently massive to extend right up to the cell-wall at all points, espe- 
cially in the case of young semi-cells. 
The number and position of the pyrenoids vary considerably amongst 
different individuals of the group, depending to a great extent on the shape 
of the chloroplast, their number being also bound up with the general 
condition of the cell. In most species which have large parietal chloroplasts 
the pyrenoids are indefinite and are scattered indiscriminately (Figs. 102 
and 129). Some species, e.g. small species of Xanthidium , have smaller 
parietal plates, each of which has typically one pyrenoid (Figs. 106, 109, 
113, and 1 15). 
1 Liitkemuller described the chloroplasts of this Desmid under the name of Docidium baculum . 
2 That Liitkemuller also noticed the variation of the chloroplasts in this species is indicated in 
some of his unpublished drawings. 
