Development, and Structure of the Vegetable Cell. 181 
new tissue-cells, I have frequently seen that all the chlorophyll- 
sacs lay completely continuous over the new septum. 
In this mode of multiplication of the joint-cells the nucleus 
of the mother cells appears to be always absorbed, whilst new 
nuclei make their appearance in the new joit-cells. 
I observed this mode of development chiefly in S. decimina 
and S. nitida. SS. orthospira is less adapted to this purpose, on 
account of the delicacy of the walls of its chlorophyll-sacs. For 
my investigations I employed slides of very thin glass, so that 
by turning them over I could examine the object on both sides, 
with high powers, without disturbing its position. 
Figs. 59-61 represent different states of S. nitida during this 
septum-formation. 
In fig. 61 the two daughter cells, still destitute of nuclei, are 
~ somewhat contracted by dilute solution of glycerine, and covered 
by the membrane of the secondary mother cell, which is lke- 
wise contracted. The chlorophyll-sacs, which at this period 
frequently, although not always, lie parallel to the septum at 
the point of contact of the two endogenous cells, are here, after 
the contraction of the daughter cells, coiled up together over 
the nucleus of their mother cell. 
In fig. 59 the nucleus of the ntother cell was seen at a in 
course of absorption, and fixed in the new septum, which was 
surrounded on all sides by the chlorophyll-sacs. 
Fig. 60 shows a somewhat more advanced stage of develop- 
ment: the new septum is here separated by the prolonged 
action of water containing carbonic acid, into two lamine, the 
thickening of which had commenced, not from the whole peri- 
phery, but from one side. After the maceration of these cells 
in solution of chloride of calcium, the portions of the primary 
cells which were not yet thickened became much swelled, and 
acquired a deep violet-blue colour with iodine. 
In the same specimens, as also in those cultivated with them, 
in which I detected, in this way, with perfect certainty, the 
multiplication of the joint-cells by endogenous cell-formation, I 
likewise frequently observed internal annular folds of the wall of 
the joint-cell, and with far greater distinctness than in the cases 
described in p. 125, as the folds here could be in general more 
readily distinguished, from their considerable thickness, which 
usually increases towards the central margin. 
When this folding existed in the lowest degree, the non- 
nucleated daughter cells were developed in about the proportion 
shown in fig. 61; between them the wall of the secondary mem- 
brane of the joint-cell sank in, together with the unaltered and 
regularly adherent chlorophyll-sacs, so far as to form a fold of 
equal depth and breadth. 
gx 
