Studies on the Chloroplasts of Desmids. II. 
BY 
N. CARTER, M.Sc. 
With Plates XIX and XX and one Figure in the Text. 
Contents. 
IX. The Chloroplasts of Micrasterias. 
I N this genus the general form of the chloroplast in some species has 
long been recognized. Thus an extensive chloroplast plate containing 
numbers of scattered pyrenoids was figured by Ralfs (1848) in several species, 
and later Delponte (1873) and W. and G. S. West (1904-11) also indicated 
the presence of ridges on the surface of the chloroplast in some other 
species. 
But although it has long been observed that in those species of the 
genus having very flattened cells the chloroplasts are correspondingly 
flattened and plate-like, in the case of those species in which the cells are 
comparatively thicker very little is known concerning the chloroplasts. 
The species whose chloroplasts have been examined during this 
investigation are M. confer ta, Lund., M. denticulately Breb., M. Tkomasiana, 
Arch., M. rotata, (Grev.) Ralfs, M. papillifera, Breb., M. radiata, Hass., 
M . Crux-Melitensis, (Ehrenb.) Hass., M. pinnatifida, (Kiitz.) Ralfs, 
M. apiculata, (Ehrenb.) Menegh., M. Americana, (Ehrenb.) Ralfs, M. oscitans, 
Ralfs, var. mucronata, (Dixon) Wille, and M. tr nne at a, (Corda) Breb. In 
spite of the fact that the chloroplasts of these species present very diverse 
appearances when examined in the front view, it has been found that they 
are all built up on the same plan. On comparing, for instance, the chloro- 
plasts of a species having very flattened cells, e.g. M. denticulata, with those 
of a species whose cells are in proportion very much thicker, e.g. M. truncata, 
considerable differences are at once apparent ; cf. PI. XIX and XX, Figs, i and 
25 ; nevertheless both can be considered as variations of one simple type. 
There is in every case one chloroplast in each semi-cell, and this consists 
primarily of an extensive flattened plate, having approximately the same 
outline as the cell-wall, and occupying a central position, its surfaces 
parallel to the front faces of the semi-cell. As a rule from both sides of 
this axile plate various ridges are given off, stretching towards the cell-wall. 
The size, number, and disposition of these ridges vary considerably according 
to the species, and even to some extent amongst individuals of the same 
[Annals of Botany, Vol. XXXIII No. CXXXI. July, 1919.] 
