304 Carter.— Studies on the Chloroplasts of Desmids . IV. 
St. anatinum , Cook and Wills ; St. sexangulare , (Bulnh.) Lund. ; St. 
Brasiliense , Nordst., var. Lundellii , W. and G. S. West ; 67. grande , 
Bulnh. ; and 67. tumidum , Breb. 
The first sixteen species agree with each other fairly well in having 
a simple axile chloroplast with a centrally placed pyrenoid such as was 
figured by Nageli (1849). In all the remaining species with the exception 
of St. tumidum , the general plan of the chloroplast is quite similar to that 
of the first large group, but there are variations in the number and arrange- 
ment of the pyrenoids, and in the number of prolongations of the chloro- 
plast running into each angle of the cell. St. tumidum has chloroplasts of 
quite different structure. 
In the simplest type of chloroplast there is a fairly massive central 
axile mass containing typically a single pyrenoid, and from this a more or 
less definite lobe arises opposite each angle of the cell (Fig. 18). Each of 
these lobes forks sooner or later, so that there are two distinct masses in 
each angle of the cell. Very often this forking is so deep that there are 
apparently two masses or plates arising directly from the axis of the 
chloroplast opposite each angle (Figs. 3, 4, 6, 8, 10, 13, &c.). 
The form of the plates often depends to some extent on the cell-wall, 
and if this is drawn out at the angles of the cell to form hollow processes or 
arms, then at corresponding points the plates of the chloroplasts are drawn 
out to form projections, often of considerable length, which are lodged in 
them (Figs. 7, 8, 34, 3^ 34, and 35). Sometimes the lobes of the chloro- 
plast in the angles of the cell are very thin and plate-like, in which case it 
not infrequently happens that each lobe forks near the periphery (Fig. 37), 
or that other smaller plates are given off from the axile mass towards the 
faces of the cell between the angles (Figs. 4 and 33). In other cases the 
chloroplast masses in the angles are so large that together they nearly fill 
the whole semi-cell, and in such chloroplasts the surface of the lobes is often 
ridged longitudinally, two, such ridges being visible in the middle of each 
face of the semi-cell (Figs. 34, 35, 34, and 35). Such differences in the 
relative mass of the chloroplast are to be correlated with variations in the 
amount of stroma starch present in it. 
Practically all the smaller species of Staurastrum examined have 
chloroplasts of this type, both those in which the angles of the cell are 
drawn out to form hollow processes, and those in which they are not. 
S. Sebaldi. 
Two varieties of this species were examined. The smaller, var. 
ornatum , Nordst., showed no deviations whatever from the simple 
chloroplast described above (Figs. 34 and 35). The larger one, however, 
var. altum , (Boldt) West, exhibited some remarkable variations in the 
number, size, and position of its pyrenoids. Unfortunately, it was only 
