The naked cells which have been alluded to live in water, and call therefore for no differentiation in connection with this necessity; but those which are surrounded by a cell-wall always develop within themselves a vacuole or cavity which occupies the greater part of their interior, and the hydrostatic pressure of whose contents keeps tha protoplasm in contact with the membrane, setting up a condition of turgidity.
In certain Trypanosomes a well-defined, usually oval vacuole is often, though not constantly, to be observed, situated at a varying distance from the anterior end (figs.
Young cells ar full of cytoplasm, old cells generally contain a large vacuole or vacuoles, containing cell-sap, and with only a thin, almost invisible layer of cytoplasm on their walls.
In the yeast cell the nucleus is represented by a homogenous granule, probably of a nucleolar nature, surrounded and perhaps to some extent impregnated by chromatin and closely connected with a vacuole which often has chromatin at its periphery, and contains one or more volutin granules which appear to consist of nucleic acid in combination with an unknown base.
(X2000.) c.g, Chromatoid grains; v, vacuole; l.s, fold or striation.
In Gnetum Gnemon, as described by Lotsy, a mature embryo-sac contains in the upper part a large central vacuole and a peripheral layer of protoplasm, including several nuclei, which take the place of the archegonia of Ephedra; the lower part of the embryo-sac, separated from the upper by a constriction, is full of parenchyma.
The cells in which the fungoid organism is vigorously flourishing are exceedingly active, showing large size, brilliant nuclei, protoplasm and vacuole, all of which give signs of iptense metabolic activity.
A curious adaptation seems to occur in certain floating forms, in the presence of a gas-vacuole, which may be made to vary its volume with varying pressure.
In Polia the connective tissue enclosed in the external muscular layer is eminently vacuolar - all the intermediate stages between such cells in which the vacuole predominates and the nucleus is peripheral and those in which the granular protoplasm still entirely fills them being moreover present.
They possess a delicate Laticiferous layer of protoplasm, with numerous small nuclei lining Tissue the walls, while the interior of the tube (corresponding with the cell-vacuole) contains a fluid called latex, consisting of an emulsion of fine granules and drops of very various substances suspended in a watery medium in which various other substances (salts, sugars, rubber-producers, tannins, alkaloids and various enzymes) are dissolved.
In other forms such as Elodea, Nitella, Chara, &c., where the cytoplasm is mainly restricted to the periphery of the sap vacuole and lining the cell wall, the streaming movement is exhibited in one direction only.