CY'ANOPHYTEIE (Neo - Lat. nom. pl.. from Gk. taiavoc, kyanos, dark-blue + Otcac, phykos, seaweed). The lowest of the four great groups of algw. They are called blue-green from the prevailing color of the cell contents, which are tinted by a diffused blue pigment named phycocyan. The eell-structure is very simple, agreeing in this respect with the Bacteria (q.v.). For details of cell-structure and classi fication, see ALG.E.
Many of the Cyanophyeew are one-celled, or consist of indefinite aggregations of cells situated in a common gelatinous matrix. Other forms are filamentous, and some are elaborately branched. A well known unbranched form is Oscillatoria, interesting because of the move ments of the tip of the filament, which swings in a circle. Nostoc forms large gelatinous balls filled with convoluted chains of cells. Certain cells in some filamentous forms lose their protoplasmic contents, becoming the so-called heterocysts, whose functions are not well understood; but they are responsible in many eases for the branching of the filaments, because the hetero cysts become firmly fastened to the sheaths that inclose the vegetative cells. The growth of the latter causes such pressure between the fixed determined by the heterocysts, that the sheath is ruptured and the filament grows out at one side. Such branching is termed 'false branching.' Branches or portions of filaments that break off and start new plants are called hormogon ia The Cyanophycea' are especially fond of warm shallow water, although many grow in damp sit uations on land, such as spray-wet rocks, damp timber, and earth. They live among the reeking
vegetation of salt marshes, and flourish in open sewers and drains. The fouling of shallow res ervoirs in warm weather, when they give off the well-known `pig-pen odor,' is generally due to growth of Cyanophyeete. The only remedy is to deepen the water.
One of the most remarkable displays of Cyano phyeere is in warns springs, well illustrated in Yellowstone National Park, where' the growths are brilliantly colored. Here certain species grow luxuriantly in water at a temperature of 75° C. and above, conditions which no other forms of alga, can endnre.
Another conspicuous display of blue-green algal is the water-bloom or scum that fre quently covers the surface of ponds and small lakes. Most of the water-blooms are due to Cyanophycefe, and the largest of all has given name to the Bed Sea, whose tint is due to the presence of a flocculent sediment made up of bundles of short filaments of Trichodesmium. This peculiar condition of the ocean is not con fined to the Red Sea, but has been reported off the coast of Brazil and South Carolina, and in the Indian and Pacific oceans.
The best monograph on the Cyanophycew is Bonnet. and Flahault, Yostocacc'es lIcicrocyWcs (Paris, 18S6-SS).