3 16 Carter . — Studies on the Chloroplasts of Desmids. IV. 
parietal chloroplasts, these were originally derived in a similar manner, and 
during the course of ages have become permanent. 
Thus the fact that the chloroplast, during cell-division, streams so 
rapidly through a usually very narrow isthmus from the older semi-cell into 
the new one, offers many opportunities for variation in its form, and it is 
really surprising that in so many species the structure of the chloroplast is 
characteristic and constant. Considering that every chloroplast is derived 
from an original small bud of green material squeezed through a narrow 
passage one would expect a large proportion of abnormalities, and for this 
reason, at any rate, it would seem unwise to make the form of the chloro- 
plast in this group the basis of a classification. 
Summary of the Special Characters of StaVIastrum. 
Most species of Staurastrum have axile chloroplasts. The only species 
examined which always has parietal chloroplasts is St. tumidum. 
Many of the smaller species have a simple axile chloroplast consisting 
of a central axis which contains a single pyrenoid and a bilobed mass 
projecting into each angle of the semi-cell. * 
Amongst the larger species the general form of the chromatophore is 
often quite similar to that of the smaller ones, but there are variations in 
the number of plates in each angle and also in the number and arrangement 
of the pyrenoids. 
Most of the species examined had one point of pyrenoid formation in 
the centre of the semi-cell, but in a few species the pyrenoids occur either in 
the angles only, or else in addition to those in the centre. 
St. Brasiliense and St. grande differ from most of the other species 
examined in their very numerous pyrenoids. 
In St. grande also some individuals show a tendency to the parietal 
disposition of the chloroplast by the total disappearance of the axis in the 
centre of the semi-cell, leaving the peripheral lobes of the chloroplasts 
isolated. 
Summary (5f the Characters of Cell-division. 
The chloroplasts of Netrium and Cylindrocystis probably behave 
during cell-division in a manner essentially similar to that already described 
by Lutman for Closterium. 
In all the Placoderm Desmids examined the process of cell-division 
is rather different from that of the Saccodermae. The nucleus of the cell 
completes its division, and the two new colourless semi-cells can readily be 
distinguished before there are any visible changes in the chromatophores. 
The latter then rapidly stream through the isthmus from the old semi-cell 
into the new one, so that by the time it is fully formed it is usually uniformly 
green. The process is completed by the division of the chloroplasts at the 
isthmus of each individual. 
