_Chlorococcum muror´um_ forms a somewhat similar but soft and thin green layer, upon damp walls or other porous bodies. It consists of very minute oval green cells, with thick walls, and imbedded in the ends of prolongations of a gelatinous matrix. _Palmel´la cruen´ta_ (Pl. VI. fig. 25) forms a portwine-red layer at the bottom of damp walls or on the ground. It is composed of pale red cells, imbedded in no definite order in a colourless gelatinous matrix. The cells are filled with red granules, and are often found undergoing division. Pl. VI. fig. 19 represents a species of _Glœocap´sa_, in which the cell-envelopes do not soften and unite to form a gelatinous matrix, as in _Palmella_ and other members of the family, but are persistent. This species occurs in fresh water containing Confervæ. CHARA´CEÆ.--This family consists of the single genus _Chára_, the systematic position of which is not agreed upon by authors; as however its structure will be better understood after what has been gone over, it may be conveniently considered here. There are several species of _Chara_, the one illustrated, _Chara vulgáris_ (Pl. VI. fig. 21), being commonly found in ditches and pools. It consists of long main stems, often a foot in length, which are branched, and surrounded at tolerably regular intervals by whorls of branchlets. In some species, the stems and branches consist simply of elongated cells, arranged end to end; while in others, of which _Chara vulgaris_ is one, the central cells are surrounded by a number of narrower spirally arranged cells, forming an outer coating. The Charæ have long formed interesting microscopic objects, on account of the circulation of the protoplasm being visible in the cells, as in the hairs of _Tradescantia_. This is best seen in those species in which the outer layer of cells is absent from the stems, and which were formerly arranged in a separate genus (_Nitella_). But it may also be seen in the stems and especially the young branchlets of any of the other species; and as the granules of the protoplasm are large, the phenomenon is more easily witnessed than in _Tradescantia_.