Development, and Structure of the Vegetable Cell. 411 
although at first slowly and in an altered form ; for from it, just 
as from a germ-cell, a perfect individual is produced. 
The first perceptible change in the cell is‘a state of tension of 
each of its free transverse walls or septa. These transverse 
septa present, in the normal uninjured state of the Conferva, a 
flat disk; but after the section of the neighbouring cells, they 
become somewhat expanded and pressed outwards from the ends 
of the uncut cell, so that they present a concavity towards the 
interior of this cell (Pl. VI. figs. 30, 31). 
This extension, which is at first exerted equally on both walls, 
soon acts only upon one of them, and this is always the one 
which is naturally the lower one—a circumstance which can be 
best verified in such sections as have a cell branching from 
them (figs. 80, 31, 42). The enlarging uninjured cell now 
usually first of all pushes the original lower septum further down- 
wards, within the cut cylindrical lateral wall, the diameter of this 
eylinder being generally not entirely occupied, by which circum- 
stance the progress of the enlarged transverse septum may be 
distinguished far downwards. This inferior prolongation of the 
cell gradually becomes smaller in diameter and thinner than 
its upper portion (figs. 33, 34, 35), and it is also frequently not 
so thickly occupied with chlorophyll (figs. 42, 45) as are the 
normal joint-cells of the plant. At the same time the inferior 
extremity of this prolongation usually affixes itself to some dead 
or living organic body, it may be to a living cell of its own spe- 
cies, extends itself upon this in thin ramifications, and adheres 
closely to it (Pl. VI. figs. 43, 44, 45), by becoming intimately 
amalgamated, without, however, exerting any perceptible influ- 
ence upon its vital activity. This direct inferior prolongation 
of the Conferva-cell thus becomes its radical extremity. 
The upper end of the same cell follows an entirely different 
course. At first, indeed, the septum exhibits a certain degree 
of extension like the lower one, but I have never distinctly made 
out a direct elongation of the apex of the cell upwards into the 
empty cell above; but when an act of growth is established in 
_ the upper extremity of the cell (an event commonly subsequent 
to the extension of the lower end), this expends itself laterally 
below the transverse septum so as to produce a branch,—the 
proceeding resembling that whereby ramifications are normally 
produced in uninjured Confervee. 
The branch therefore is developed within and under cover of 
the original enveloping membrane of the entire plant, whilst, on 
the contrary, the organ which represents the root of the higher 
plants is not covered by this general integument, but, so soon as 
it has emerged from the surrounding walls of the cut cell, con- 
tinues to elongate itself in the water quite free and unclothed. 
27% 
