Carter —Studies on the Chlor op lasts of Desmids . IV. 307 
points a single chloroplast plate given off from the axis forked into two 
horizontally, one part supplying an arm of the upper whorl, and the other 
a corresponding arm of the lower whorl (Fig. 28, a , a! ; b, b r ; d, d f ; e\ &c.). 
But as there are nine arms in the lower whorl and only six in the upper, it 
is obvious that the arms cannot be associated in pairs, one belonging to 
each whorl, all round the semi-cell, and on closely examining the chloroplast 
it is found that there are two distinct kinds of plates given off from the 
central axis. The larger plates stretch nearly from end to end of the 
chloroplast and are drawn out at their upper and lower extremities to form 
. two prolongations which enter corresponding arms of the upper and lower 
whorls (a, at ; b, b ' ; d, d', &c.). There are a.lso shorter ridges, mere 
projections which enter certain arms of the lower whorl only, and do not 
extend as far up as the upper whorl (c, f i , &c.). Altogether there are six 
larger plates and three smaller ones in each semi-cell, and they alternate 
regularly, two of the former and one of the latter all round the semi-cell. 
St. anatinum and St. sexangidare. 
Here the chloroplasts differ considerably from those of the other 
species examined in the relative size of the axis and the plates which 
radiate into the angles. The central axis is very much reduced, and by far 
the greater part of the chloroplast is to be found in a more peripheral 
position in the angles of the cell. Consequently the pyrenoids are not, as 
before, in the centre of the cell, but in the much larger masses of chloro- 
plast in the angles (Figs. 20 and 44). 
St. anatinum is triangular in end view, and there are consequently 
three masses of chloroplast, one in each angle, which towards the centre of 
the cell become abruptly very much thinner, being all united by a very 
narrow surface in the middle of the cell. Towards the periphery each mass 
forks to form two projections which do not extend very far into the hollow 
processes of the cell-wall (Fig. 20). There are typically three pyrenoids in 
each semi-cell, one in each angle, but frequently one or more of them 
divide to form a little group in well-nourished cells. 
The chloroplast of St. sexangulare corresponds in all important respects 
to that of St. anatinum. In the material examined each semi-cell was 
provided with ten hollow processes arranged in two whorls of five, and the 
cells in end view were pentagonal, corresponding arms of the two whorls 
being on top of each other (Fig. 44). As before, the greater part of the 
chloroplast is situated in the angles, and not in the centre of the cell, and 
there are accordingly five masses of chloroplast, one in each angle, and each 
containing a pyrenoid. All five masses are connected up in the middle of 
the cell, and towards the periphery each one forks to form two plates, which 
stretch out towards the angles (Fig. 44). But in this case there are two 
hollow processes at each angle, and so the two plates in each angle of the 
