Carter —Studies on the Chloroplasts of Desmids. IV, 309 
In the case of specimens showing parietal chloroplasts it is possible 
that the change in form occurred in the first place in young semi-cells during 
cell-divisions. For in Staurastrum it often happens that during cell- 
division the more peripheral lobes of the chloroplast bud into the young 
semi-cell from the old one much more quickly than the central axile part, 
streaming up over the quickly growing cell-wall and covering it in a parietal 
manner, as if the mantling of the whole surface of the cell-wall with photo- 
synthetic material were the most important thing to get completed, and as 
long as this were accomplished the growth of the more central part of the 
chloroplast would be of secondary importance. Thus even in species with 
centrally placed pyrenoids it is frequently seen in young though quite full- 
sized semi-cells that the real axis of the chloroplast is exceedingly short, 
and that the plates radiating from this stretch up towards the apex and 
angles of the cell, almost completely enclosing a large colourless space in 
the upper region of the semi-cell. This is even more pronounced in 
St. anatinuniy where the central axis contains no pyrenoids and is conse- 
quently, in any case, not of such vital importance to the young semi-cell. In 
young semi-cells of this species the central axis in some cases does not exist, 
and even in some fully grown semi-cells, after the division of the chloroplast 
at the isthmus between the old and the young semi-cells, it is only repre- 
sented by an exceedingly short length near the nucleus, the radiating 
plates arising up from this and arching over the cell-wall of the angles in 
a parietal manner very suggestive of the parietal chloroplasts often observed 
in certain cells of St. grande. It seems possible that, in the very short 
semi-cells of St. grande particularly, the division of the chloroplast at the 
isthmus after cell-division may occasionally occur actually before the axis of 
the chloroplast has entered the new semi-cell at all, while yet the more 
peripheral parts of the chloroplast have already streamed in from the old 
semi-cell to the new, and well covered the young cell-wall. The shape of 
the semi-cell, with its bulging angles and extreme shortness, would seem to 
be very conducive to this, for it is quite possible that the peripheral parts 
of the chloroplast, whilst creeping up round the cell-wall of the angles of 
the young semi-cell, might be cut off from the more central part of the old 
chloroplast by the sudden division of the chloroplast at the isthmus. This 
idea is supported by the fact that in some individuals the chloroplasts in one 
semi-cell are parietal, whilst in the other there is only one chloroplast which 
is axile. 
This strong tendency to variation in the disposition of the chloroplasts 
during cell-division makes it absolutely impossible for any reliable system 
of classification to be based on the characters of the chromatophore, such 
as was attempted by Lundell and Lagerheim. 
