Development, and Structure of the Vegetable Cell. 433 
The constricted line of union between the two connected 
daughter cells is not unfrequently colourless; nevertheless it 
cannot be positively ascertained whether, as appears upon alter- 
ing the focal distance, and as would correspond with my notion 
of the origin of the septum, the circularly torn thickened septum 
is continued as a delicate membrane throughout this uniting 
band, or whether a fluid constitutes the stratum of separation 
between the coloured secretion-matter contained in the two 
daughter cells. 
In most instances, even this connective band is concealed by 
the coloured contents, which are pressed into the median line 
by the contracted membranes of the secondary cells ; and in these 
circumstances the scar of the lacerated septum exhibits the 
appearance of a notch in this lamina in the mass of chlorophyll. 
The appearances in cells where new septa are im course of 
lignification are altogether different when rather stronger dios- 
motic agents are brought into contact with them. In such cases 
one of the young joint-cells is frequently more strongly con- 
tracted than its neighbour; the delicate septum perceptible be- 
tween them, which usually, in its youngest and unthickened 
condition, protrudes in a convex form into the upper cell (PI. VI. 
fig. 42 a), does so, under the condition in question, to a greater 
degree ; the contiguous secretion-vesicles hkewise gradually re- 
cede into the less extended cell, until at length the septum can 
no longer withstand the constantly increasing pressure, but 
gives way before it, and allows a sudden rush of the chlorophyll- 
and starch-corpuscles from their cavity into the neighbourmg 
one. These phenomena may be readily witnessed in the vicinity 
of the cut portions of the joint-cells (p. 421). 
This translation of the chlorophyll- and starch-corpuscles from 
one side of the septum to the other, within the expanding cell, 
and which may especially be seen for a considerable time after 
the rupture of the septum, might lead those who do not take 
into consideration the great extensibility of the unthickened 
cell-wall, and who may not have observed the ultimate rupture 
of the young septum, to the erroneous belief that no septum 
existed betwixt the two closely approximated and contracted 
daughter cells. 
However, if, after extension has proceeded for a time, the 
abrupt and forcible movement of the chlorophyll-vesicles, &c. 
be first observed, followed by a more gentle one, the opera- 
tion of diosmosis remaining unchanged, no other inference can 
be drawn than that an existing obstacle has been suddenly re- 
moved, and evidence thereby afforded of the previous existence 
of a septum, overlaid by those secretion-vesicles, at the spot 
where the movement occurred. 
