Ul´va latis´sima is very common on the sea-coast, being found attached to stones, shells, &c. It forms a broad, flat, green, rounded or oblong, thin frond, wavy and crumpled at the margins, and from 6 to 18 inches in length. The minute cells form two layers, adherent to each other. The zoospores formed are numerous in each cell.
Enteromor´pha compres´sa ([Pl. IV.] fig. 31) is also common in the sea and in brackish ditches; it is often found floating. The frond is green, tubular, flattened or compressed, and branched, the branches being usually simple and narrowed at the base. The frond consists of two layers of minute cells, separated by a space rendering it hollow. The zoospores are numerous in the cells (fig. 32).
Palmella´ceæ.—These Algæ are found in fresh or salt water, or on damp earth, wood, &c. They are green or red, forming round or irregular masses or strata. They consist of loosely connected cells, imbedded in a gelatinous mass or matrix, thus forming a frond.
Chlorococ´cum vulgáre ([Pl. II.] fig. 1) is very common upon the bark of elm-trees, palings, &c., forming a green granular crust. It consists of minute rounded or oval cells, mostly undergoing division into twos, fours, or eights. These cells are attached to the sides or ends of very fine colourless filaments. It is most probable that this organism, which is usually placed among the Algæ, consists of the gonidia of a Lichen.
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.