| 
: 
: 
: 
| 
Development, and Structure of the Vegetable Cell, 425 
velopment, and left only their final and most highly developed 
products, in the shape of small vesicles freely moving within the 
juices of the cell, and destined for the nutrition of new joint- 
cells. 
If such joint-cells, furnished with annular folds (fig. 40 0), 
be examined for some time, progressive, though very gradual, 
changes are observed to take place in the position of the secre- 
tion-vesicles. Here and there in the vicinity of the annular fold 
the sharp outline of a cell, apparently filled with colourless fluid, 
will make its appearance among the mass of secretion-material 
which occupies the joint-cell. This enlarges, and progressively 
advances towards the middle line of the fold. A similar process 
may be frequently witnessed going on simultaneously on the 
other side of the fold. 
Lastly, the entire and somewhat rounded end of the cell may 
be observed free from chlorophyll close to the fold; the mem- 
brane, as compared with that of other young cells, is thick, but 
of a gelatinous aspect, whilst the contiguous thick membrane of 
the fold resembles that of woody tissue. 
The two endogenous cells at last approach so closely together 
in the middle line of the fold, that, by their mutual pressure, 
they form a septum which, to those who have not followed its 
development, would appear as if it had been forcibly separated 
at its periphery by the annular fold. 
In other cases, a cell arises on one side only of the fold, and 
continues to elongate itself beyond this, until it reaches the next 
Septum. 
The membrane of the fold appears, during the subsequent 
existence of the endogenous cells, to become absorbed; for we 
find that where these latter have thick walls, the former is thinner 
than when those cells were newly formed. 
This mode of formation of septa by tolerably thick-walled 
endogenous cells, readily observable during their slow growth, 
is, however, of comparatively rare occurrence in Cladophora 
glomerata. Usually, in this plant, the commencement of thick- 
ening first calls attention to a pre-existent and fully developed 
although very delicate septum, this having been previously con- 
cealed from observation by the great quantity of secretion~ 
materials with which it is covered. 
In my account of the structure of Vaucheria, I showed that 
this so-called unicellular plant consisted of a composite system 
of endogenous cells, the innermost of which develope themselves 
and enclose organized secretory materials simultaneously with 
the absorption of the mother cells with their contents, but that 
the membranes of all these joint-cells do not become thickened, 
and therefore may easily be overlooked. 
Ann. & Mag. N. Hist. Ser. 3. Vol. xiii. 28 
