Chara

Chara, a genus of plants of great botanical interest. They are aquatics occurring in fresh or brackish waters, especially when stagnant, in most parts of the world; and are often much encrusted with lime, so as to become brittle, and are hence known as stone-worts. Their stems, which rise from the bottom often through several feet of water, are very slender, consisting of internodal cells, often several inches long, surrounded by a circle of cortical cells and separated by nodes, from which spring the cortical cells, whorls of branches, and the sexual organs. The cortex is developed upwards and downwards from each node so as to meet that from the next node halfway along the internode. The cells contain numerous chlorophyll-grains which exhibit very clearly the rotation of the protoplasm. Growth takes place by the division of a large apical cell. The reproductive structures, both of which are red when mature, are very distinct from those of any other groups of plants. The antheridium or globule is a minute stalked sphere, enclosed by eight much-lobed cells, called shields. From the centre of each shield a cell, called manubrium, or handle, proceeds towards the centre of the sphere, bearing a round cell or capitulum which in its turn bears six secondary capitula, each bearing four long filaments. Each filament, there being in all 192, consists of between 100 and 200 cells, each containing a spirally-coiled antherozoid, resembling those of mosses. The archegonium or nucule consists of a central cell, surrounded by five twisted cortical cells surmounted by five small cells forming the teeth of a coronet. After the antherozoids have made their way between these and fertilised the central cell, the whole nucule falls off and germinates like a spore, forming a pro-embryo, or cell-filament, from a bud on which a new plant originates. Nucules of Chara occur as fossils in Tertiary rocks, and are known from their markings as gyrogonites. Chara is now generally classified either near the mosses or among algae.