among the algae of protecting the overwintering zygote within the tissues of the parent gametophyte is one of several characteristics of Coleochaetales that suggest that they are a sister group to the embryophytes. The Charales or stoneworts are freshwater algae with slender green or grey stems; the grey colour of many species results from the deposition of lime on the walls, masking the green colour of the chlorophyll. The main stems are slender and branch occasionally. Lateral branchlets occur in whorls at regular intervals up the stem, they are attached by rhizoids to the substrate. The reproductive organs consist of antheridia and oogonia, though the structures of these organs differ considerably from the corresponding organs in other algae. As a result of fertilization, a protonema is formed, from which the sexually reproducing algae develops. Charophytes are frequently found in hard water with dissolved calcium or magnesium carbonates. They tolerate low concentrations of salt, and are found in the inner reaches of the Baltic Sea and in tropical brackish lagoons but not in marine environments. The water must be still, or only slow-flowing, oligotrophic or mesotrophic and little pollution due to sewage. The Charophyceae are obligate aquatic algae, growing submerged in calcareous fresh water. They are distributed throughout the world from the tropics to cold temperate zones. Six genera are recognized: Chara Lamprothamnium Lychnothamnus Nitella Nitellopsis Tolypella. Cell structure There are numerous small discoid chloroplasts, which are disposed around the periphery of the cells. No pyrenoids are present. The large internodal cells are sometimes multinucleate, and their nuclei often possess large nucleoli and little chromatin. In these cells, the cytoplasm forms only a peripheral layer with a large central vacuole. The cell walls are composed of cellulose, though there may be also a superficial layer of a more gelatinous material of the unknown composition. The storage material is starch, except in the oospore, where oil also occurs. This starch also accumulates in special storage structures, termed bulbils, which consist of rounded cells of varying size which are developed in clusters on the lower stem-like and root-like nodes. They are mainly developed when the algae are growing in fine slimy mud. Cytoplasmic streaming was first demonstrated in the giant cells of Chara internodes by Giovanni Battista Amici, in 1818. Their body organization is three-dimensional, however, there is no full division of labour thus are thaloids. Sexual reproduction The reproductive organs of the