250 Carter . Studies on the Chloroplasts of Desmids. /, 
B. Summary of the Special Characters of T ETMEMORUS. 
The chloroplast in Tetmemorus is essentially similar to that of Closterium 
in consisting of a central axis containing pyrenoids and a number of 
radiating ridges. 
In T. Brebissonii the ridges thicken abruptly towards the periphery, 
forming longitudinal parietal bands of considerable width. 
T, granulatus and T. laevis have simple ridges which do not form such 
extensive parietal masses, but end with toothed edges, or are provided with 
attenuated projections which stretch towards the cell-wall. When little or 
no stroma-starch is present in the chloroplasts of these two species, the 
ridges often undulate in a manner similar to that occurring in certain 
species of Closterium. 
C. Summary of the Special Characters of Eua strum. 
With the exception of Eu. verrucosum the chloroplasts of all the 
species examined can be considered as variations of one type. At the 
same time they naturally form two distinct groups. 
The smallest species examined form Group I. They have a relatively 
large axile mass of chloroplast containing typically one pyrenoid, and from 
this four, main lobes project towards the periphery. These lobes are in the 
very smallest species quite small and insignificant, but in the larger species 
of the group they are somewhat larger and may be branched. 
Group II contains most of the largest species examined. Here the 
structure of the chloroplast is essentially similar to that of the first group, 
but the real axis of the chloroplast is very thin, and the peripheral lobes 
spread out to form a thick layer lining the cell-wall, so that the greater 
mass of the chloroplast is in the parietal position. The pyrenoids, instead 
of occurring in the centre of the semi-cell as in the first group, are to be 
found in the more massive part of the chloroplast forming the parietal 
plates, the interior of the cell being often quite free from them. Following 
on the decrease in importance of the axile part of the chloroplast in Group II 
is a decided tendency for it to disappear altogether, leaving only the parietal 
mass of chloroplast with its pyrenoids lining the cell-wall. Transitions 
from the axile to the parietal condition of the chloroplast were observed in 
most of the larger species examined. 
In the case of Eu. verrucosum there are two distinct axile chloroplasts 
in each semi-cell, each with a large central pyrenoid, as in many species of 
Cosmarium. The structure of its chloroplast suggests that it has no very 
close affinities with any of the other species of the genus examined, but if 
other related species could be investigated, its extraordinary structure would 
possibly be explained. 
