Carter . — Studies on the Chlor op lasts of Desmids. III. 267 
or plates containing the pyrenoids are in some cases covered with tiny 
outgrowths of chloroplost stretching towards the cell-wall. He found that 
in C. tessellatum these outgrowths were arranged in a definite relation to the 
warts on the external surface of the wall, each outgrowth being exactly 
under a wart, but he observed that such outgrowths were also present in 
species which are not provided with such nodules, e g. C. turgidum , C. de 
Baryi. Lutkemiiller was unable to give any explanation for the occurrence 
of these outgrowths, and raises the question whether they are characteristic 
of Lagerheim’s genus P leurotaeniopsis , observing that he had not been able 
to ascertain the presence of such outgrowths on the parietal chloroplasts of 
any species of Xanthidium , Pleurotaenmm , or Spirotaenia he had examined. 
During the present investigation similar outgrowths have been observed in 
species of Pleurotae ilium , Euastrum , Xanthidium , and also in other species 
of Cosmarium , so that this character cannot be considered unique to Pleuro - 
taeniopsis. It is possible that this formation of outgrowths is a convenient 
method of increasing the surface of photosynthetic material exposed to the 
exterior. It only occurs in chloroplasts which are fairly massive. Where 
only a delicate film of chloroplast is present such outgrowths never occur, 
because the whole of the chloroplast is sufficiently exposed to the light. But 
if there is a fairly thick layer lining the cell-wall, then part of it is projected 
outwards in the form of outgrowths. Obviously this arrangement is much 
better than having a simple thick layer of chloroplast. The relation in some 
species of the outgrowths to the warts on the cell-wall is a rather more 
difficult problem, since many species having no warts are provided with 
outgrowths, and in at least one species having warts, Cosmarium Brebissonii , 
the outgrowths are not arranged in any definite relation to these. 
With regard to the pyrenoids, there has been some misunderstanding 
concerning the number of these bodies occurring in the genus. It was 
formerly believed that, excluding those species having parietal chloroplasts, 
all other species of Cosmarium were provided either with one or two 
pyrenoids in each semi-cell. The first investigator to show that this rule 
was not without exception was Lutkemiiller (1893), who reported the 
presence of unusually large numbers of pyrenoids in C. pyramidatum and 
a few other species. 
Later, Ducellier (1917) made further observations supporting those of 
Lutkemiiller. He also attempted to show that there is some relation 
between the actual size of the cell and the number of pyrenoids contained in 
it, examining several species of the genus in order to prove that individuals 
containing an unusually large number of pyrenoids are often larger in size 
than individuals of the same species having fewer pyrenoids. 
Although it may be true, in general, that large-celled species often 
have more pyrenoids than the smaller ones, it can scarcely be true in the 
