Development, and Structure of the Vegetable Cell. 421 
in figs. 836 & 38, only the central and less thickened or entirely 
unthickened portion of it, inflating it at first im a globular form, 
and subsequently occupying more or less completely the entire 
space of the lower cell. 
In the normally developing septum the increase of volume of 
the assimilating and growing cell-membrane (fig. 40 a), which 
manifests itself as a thickening, commences at the periphery, 
and advances hence in the cylindrical part of the membrane to- 
wards the ends of the two cells, in accordance with the growth 
of their mother cell ; in the septum itself the advance is towards 
its central point. 
If, by the stronger endosmotic distention of the neighbouring 
uninjured cells, a greater pressure is exerted, soon after the 
cutting of the cell, upon a septum of this kind which has not 
long become liquefied, the septum is not grown through as 
above described, but it is suddenly ruptured, and the contents 
of the neighbouring and previously uninjured cells are pressed 
out through the opening. 
A similar laceration of the new septal wall and escape of the 
contents of a cell into the neighbouring cells, after the operation 
of endosmotic fluids, takes place also in uninjured cells, and 
appears to have furnished earlier investigators with support for 
the idea of a septal formation by the growing in of a fold of the 
parietal part of the membrane of the mother cell as far as its 
middle line. 
Sometimes the downward-growing lower end of the upper cell 
does not thrust the transverse wall before it in the median line, 
but to one side, so that its lengthening extremity presents on 
one side a very narrow, and on the opposite a much wider, an- 
nular fold as the remnant of the original septal wall (figs. 37 
& 39a). 
I have more frequently observed instances where the down- 
ward growing cell has not prolonged itself within the next dead 
or cut cell beneath, but has thrust this entirely to one side, so 
that the two cells appear in apposition, longitudinally, like two 
wedges lying in opposite directions. 
Sometimes connected Conferva-filaments are met with in 
which some single cell has become diseased and withered, and 
then the immediately superior cell has grown in the form of a 
root-cell into the cavity of the diseased cell, down to its bottom, 
forming the next lower septum. This portion which has grown 
down then begins to enlarge, until it entirely fills the cavity of the 
diseased cell, and its lower extremity forms a perfectly normal 
septum with the neighbouring cell. 
The very long joint-cells thus formed become, just as in the 
case of the root-like cells produced from injured Conferva-cells, 
