Development, and Structure of the Vegetable Cell. 417 
and iodine is employed, when the shrivelled membrane is scarcely 
coloured pale yellow. 
Moreover these phenomena are modified not only by the 
stage of development of the plant, but probably also by variations 
in the conditions of nutrition, as the researches on Sprrogyra, 
hereafter to be described, have further shown. 
From the foregoing remarks it follows that the joint-cells of 
Cladophora glomerata do not contain at all periods of their de- 
velopment a mucilaginous, granular, viscid fluid—the “ goni- 
mical contents” of Kiitzing or the “ protoplasm” of Mohl; but 
that, at certain periods, they are entirely filled, as if occupied 
by a perfect cellular tissue, with thin-walled strongly diosmotic 
cells, which, on the one hand, enlarge in water with extraordi- 
nary rapidity, and, on the other, shrivel up in solution of gum. 
The nature of these endogenous cells is twofold. Thus some 
of them contain, besides a colourless watery fluid, often also 
without this, a larger or smaller quantity of a green mucilaginous 
matter (both materials being very probably enveloped in special 
cell-membranes), and, floating freely in the latter substance, 
either small vesicles of starch and chlorophyll (the latter frequently 
containing a starchy nuclear vesicle) or smaller and larger cells, 
in which these bodies are then contained. Their membrane is 
distended, and soon becomes liquefied im water. 
The cells of the second description are filled only with a clear 
transparent liquid, and very rapidly absorb water until they are 
burst and destroyed by it. They are therefore difficult of ob- 
servation, unless the water is duly mixed with gum, so as to 
retard the distention of the diosmotic membrane, when it be- 
comes possible at times to demonstrate that the membrane of 
many of these cells is corroded, but not dissolved, by water and 
solution of chloride of zinc and iodine. 
Between these two kinds of cells intermediate forms occur, 
showing that the two forms are not of an entirely different 
nature, but only different stages of development of one and the 
same kind of cell. 
The phenomena observed during the action of fluids on the 
cut joint-cells and on the expanding endogenous cells which 
issue from them, as also the position of the latter in the unin- 
jured and normally grown joint-cells, indicate that the cells 
consisting of watery contents and more resistent membranes 
occupy the median line of the cylindrical joint-cell of the Con- 
ferva, whilst those filled with chlorophyll, and whose membranes 
are soluble in water, occur nearer to the surface than this central 
tissue. 
Moreover, at the extremities of the joint-cells of perfectly 
normally developed plants, the limpid cells—pressed together 
