Carter. — S (tidies on the Chloroptasts of Desmids. III. 273 
centre of the chloroplast between them. He thought that this rupture was 
brought about by the travelling towards the periphery of the products of 
division of an original central pyrenoid, a single pyrenoid being, according 
to his theory, general at first in all individuals. Whether or not this is so 
could not be ascertained without the examination of actively dividing 
material, but considering the behaviour of the chloroplasts of other species 
during cell-division it seems most likely that, since there are nearly always 
two pyrenoids at the base of the semi-cell, either these, or possibly in some 
cases the products of their division, would enter the new semi-cell when cell- 
division took place, whilst in the case of individuals containing as many as 
fourteen pyrenoids in a half-cell, the new semi-cell would doubtless be 
supplied with quite a number of pyrenoids. It is most likely, therefore, 
that the semi-cells of C. pyramidatum often contain originally at least two 
pyrenoids, in which case the travelling apart of the products of division of 
an original central one could not explain the formation of the central hole. 
Although it was observed that the axis of this species is always very 
delicate, consisting sometimes merely of a delicate reticulum, a cavity such 
as was described by Liitkemuller was never noticed in such material as was 
available. It is possible that such a delicate structure could not be detected 
in the living condition, and that this accounts for Lutkemiiller’s statement. 
Ducellier (1917) reports that one collection of this species examined by 
him contained quite a large proportion (30 per cent.) of individuals having 
only one pyrenoid in a semi-cell. This may have been a special character 
developed in that particular locality, for it is quite possible that occasionally 
in newly-divided specimens the young semi-cell is only provided with one 
pyrenoid, especially in those forms containing very few pyrenoids. In 
Ducellier’s collection there were never more than two pyrenoids in each 
semi-cell. It must be remembered that the chloroplast has to push its way 
from the old semi-cell through the comparatively narrow isthmus into the 
young, semi-cell after cell-division, and therefore one must not be surprised 
if distortions sometimes occur. Thus it is quite possible that, following 
such an abnormal division, the young semi-cell is found to be provided with 
only one pyrenoid, and repeated division might result in the production of 
quite a large proportion of such individuals containing only one pyrenoid in 
a semi-cell, as in Ducellier’s collection. Nevertheless it seems true that as 
a rule there are two or more pyrenoids in the chloroplasts of this species, 
and that the axis of the chloroplast is usually very delicate, so that the actual 
centre of the semi-cell is usually destitute of pyrenoids. 
C. achondroides. 
This species was originally described and figured by West (1909) as 
having parietal chloroplasts. A subsequent examination of stained speci- 
mens has shown, however, that there is actually one axile chloroplast in each 
