308 Carter. — Studies on the Chloroplasts of Desmids. IV. 
semi-cell are drawn out at their upper and lower extremities to form four 
projections^ the two upper entering the upper arm of the angle, and the 
two lower the lower arm (Figs. 43 and 44). 
St. Brasiliense , var. Lundellii , and St. grande. 
The chloroplast of the large species St. Brasiliense , var. Lundellii , differs 
in several ways from the ordinary type of chloroplast of the genus. The 
semi-cells are large, and are pentagonal in the end view, and there is a central 
axis of considerable size in the interior which gives rise to five much larger 
masses, one in each angle of the semi-cell. Each of these splits up towards 
the periphery to form four or five distinct though narrow lamellae, whose 
undulating margins lie against bounding walls of the angles (Fig. 45). The 
pyrenoids are extremely numerous, and are scattered throughout the central 
axis and the larger masses in the angles, occurring in six more or less 
distinct longitudinal rows (Figs. 45 and 46). 
St. grande often has a chloroplast which is in some respects very 
similar to that of St. Brasiliense , var. Lundellii. The cell is triangular in 
end view, and there is a central axis in the middle of the semi-cell which 
gives rise to three fairly large masses of chloroplast, one in each angle. 
Each of these forks into two, but the resulting plates often cling closely to 
the walls of the angle after the manner of parietal chloroplasts (Fig. 42). 
The pyrenoids are probably in typical cases seven in each semi-cell, one in 
the central axis, and one in each of the plates in the angles. They are 
usually much more numerous, however, four or five being crowded together 
in a row in the middle of the cell, and as many as six or seven scattered in 
the plates of each angle (Figs. 41 and 42). 
The chloroplast of this species shows a decided tendency to vary in its 
disposition, and not infrequently specimens in which the interior of the 
cell is quite free from chlorophyll-bearing substance are to be observed, the 
chloroplasts being confined to the angles (Fig. 39). In such cases the 
central axis of the chloroplast has entirely disappeared, the masses in the 
angles being thus isolated (Fig. 40). Sometimes these masses in the angles 
retain their form as single masses forking towards the periphery, but in 
other cases the angle may contain two distinct plate-like structures, which 
embrace the walls and are practically parietal bands (Fig. 39). In these 
chloroplasts the pyrenoids are often two in each angle, one on each side, but 
they are frequently much more numerous. Sometimes the chloroplast 
masses in the angles are very irregular in form, and contain numerous 
scattered pyrenoids (Fig. 40). 
Thus when truly axile, the chloroplast of St. grande agrees with that 
of St. Brasiliense , var. Lundellii , in its massive form, and in the arrangement 
and frequently great number of its pyrenoids. 
