Carter. — Studies on the Chloroplasts of Desmids. /. 227 
The only record of similar pyrenoids occurring in the Chlorophyceae is 
provided by Schmitz 1 ( 1882 ), who reports that in some of the thicker-celled 
species of Zygnema , very small pyrenoids are sometimes apparent in the 
peripheral ends of the rays of the star-shaped chloroplasts. Schmitz does 
not definitely say that these pyrenoids were destitute of starch, but their 
position near the cell-wall and their supposed origin de novo is very 
suggestive of the small proteid granules observed in certain Desmids. 
It is proposed to give, as far as is possible from the limited number of 
species examined, a comparative account of the chloroplasts found in each 
genus, excluding those genera in which the form of these bodies is already 
well known, and in this part of the work the genera dealt with will be 
Netrium, Closterinm , Tetmemorus , Eucistrmn , and Xanthidium. 
III. The Chloroplasts of the Genus Netrium. 
This genus belongs to the Saccodermae, and the species examined were 
N. Digitus , (Ehrenb.) Itzigs. and Rothe, N. oblongum , (de Bary) Liitkem., 
N. oblongum , var. cylindricum , West and G. S. West, and N. interruptum , 
(Breb.) Liitkem. The chloroplasts of these species are generally well known, 
and consist of a central axis from which a number of plates are given off. 
In N. Digitus these are nearly always eight in number (Fig. 15), in 
N. oblongum there are eight or nine, in N. oblongum , var. cylindriaim , about 
seven (Fig. 18), and in N. interruptum about eleven or twelve (Fig. 19), but 
except in the case of N. Digitus the counting of the plates had to be 
done from whole specimens, and so these numbers may not be exact. 
The peripheral edges of the plates in N . Digitus are more or less deeply 
cut into teeth which project alternately on either side of the plate towards 
the cell-wall (Figs. 13 and 15). The actual size and shape of the projec- 
tions vary considerably; in some cases they consist of long fine strands 
which stretch in various directions towards the cell-wall, whilst in other 
individuals they are quite fiat and angular. 
In N. oblongum the plates are similarly notched but are not quite so 
complicated (Figs. 16 and 17), and in N. interruptum the edges of the 
plates are entire (Fig. 19). .The latter species also differs from the others in 
having two chloroplasts in each half-cell. 
The pyrenoids found in these species of the genus are peculiar in several 
ways. They occur only in the central axis of the chloroplast and are 
usually of extraordinary length, there being as a rule one pyrenoid only in 
each chloroplast, which is apparent as a conspicuous darkly staining rod in 
the middle of each half-cell (Fig. 14). The amount of starch round each 
pyrenoid naturally varies very much according to the condition of the cell, 
but the starch grains are always very small in comparison with the size of 
p. 74. 
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