The protoplasm lines the wall of the cell, and extends in the form of thin plates across the cavity of the cell, dividing it up into a number of irregular chambers. Imbedded in the protoplasm are numerous flattened chloroplasts, which are so close together as to make the protoplasm appear almost uniformly green. Within the chloroplasts are globular, glistening bodies, called "pyrenoids." The cell has several nuclei, but they are scarcely evident in the living cell. By placing the cells for a few hours in a one per cent watery solution of chromic acid, then washing thoroughly and staining with borax carmine, the nuclei will be made very evident (Fig. 13, _B_). Such preparations may be kept permanently in dilute glycerine. [Illustration: FIG. 13.--_Cladophora._ _A_, a fragment of a plant, × 50. _B_, a single cell treated with chromic acid, and stained with alum cochineal. _n_, nucleus. _py._ pyrenoid, × 150. _C_, three stages in the division of a cell. i, 1.45 p.m.; ii, 2.55 p.m.; iii, 4.15 p.m., × 150. _D_, a zoöspore × 350.] If a mass of actively growing filaments is examined, some of the cells will probably be found in process of fission. The process is very simple, and may be easily followed (Fig. 13, _C_). A ridge of cellulose is formed around the cell wall, projecting inward, and pushing in the protoplasm as it grows. The process is continued until the ring closes in the middle, cutting the protoplasmic body completely in two, and forms a firm membrane across the middle of the cell. The protoplasm at this stage (_C_ iii.) is somewhat contracted, but soon becomes closely applied to the new wall. The whole process lasts, at ordinary temperatures (20°-25° C.), from three to four hours. At certain times, but unfortunately not often to be met with, the contents of some of the cells form, by internal division, a large number of small, naked cells (zoöspores) (Fig. 13, _D_), which escape and swim about actively for a time, and afterwards become invested with a cell wall, and grow into a new filament. These cells are called zoöspores, from their animal-like movements. They are provided with two cilia, closely resembling the motile cells of the _Protococcaceæ_ and _Volvocineæ_. There are very many examples of these simple _Confervaceæ_, some like _Conferva_ being simple rows of cells, others like _Stigeoclonium_ (Fig. 14, _A_), _Chætophora_ and _Draparnaldia_ (Fig. 14, _B_, _C_), very much branched. The two latter forms are surrounded by masses of transparent jelly, which sometimes reach a length of several centimetres. [Illustration: FIG. 14.--_Confervaceæ_. _A_, _Stigeoclonium_. _B_, _Draparnaldia_, × 50. _C_, a piece of _Draparnaldia_, × 2. _D_, part of a filament of _Conferva_, × 300.]