980 XIV. ALGM. 



Very obscure plants, abounding in damp places, and in various situations ; some form woolly patches, 

 or gelatinous strata of a green, olive, brown or seruginous colour ; some emit a strong odour ; some are 

 almost invariably found on dripping rocks. Vibrios are minute colourless active jointed bodies, that 

 abound in decomposing infusions, and, like the still simpler Buctmice, which are mere inflexible rods of 

 excessive minuteness, are probably rudimentary states of other Algce. 



II. NosTOCHiNEJ!. — Plants growing on damp moss or earth, and on stones in fresh water, 

 consisting of slender moniliform tranquil or oscillating filaments, composed of cells placed end 

 to end, immersed in a dense gelatinous matter, formed by the fusion of the gelatinous sheaths 

 of the filaments. Cells of the filaments of three kinds : — 1. Ordinary cells ; 2. Vesicular 

 cells, large, without granular matter, but often with erect hairs ; 3. Globose, elliptic or 

 cylindric sporangia. — Reproduction by cell-division. 



PRINCIPAL GENERA. 



Nostoc (Hormosiphon). Sphasrozyga. Spermoseira. Monormia. 



Aphanizomenon. Anabaina. Trichodesmium. 



A group of obscure plants, resembling Cottema amongst Lichens externally, found all over the globe, 

 even on ice and snow ; often occurring in detached masses. Nostoc edule is sold in China, dried, and forma 

 an ingredient in soups. Several species inhabit salt lakes in Tibet and elsewhere. Monormia forms 

 floating jelly-like masses on brackish water, sometimes of great extent. Trichodesminm, which floats 

 on the surface of the great oceans and Eed Sea, and resembles chopped straw, has been referred both to 

 this group and to Oscillatoriece. 



III. Palmellacej). — Gelatinous or powdery crusts found on damp surfaces, and in fresh or 

 salt water, composed of globular and elliptic cells, aggregated in a gelatinous matrix, increasing 

 by cell-division and by ciliated zoospores. 



PRINCIPAL GENERA. 



Chlorococcus. Protococcus. Glaeocapsa. Hormospora. 



Palmella. Trypothallus. 



Palmella crumta forms the well-known rose-coloured gelatinous patches on damp walls, which flake 

 ofi^ when dry. P. prodigiosa, which spreads over meat and boiled vegetables, under certain atmospheric 

 and other conditions, with alarming rapidity, is probably not an Alga. Protococcus includes various uni- 

 cellular Palmellacecs, which increase by division into two or four parts, which separate, but are connected 

 by a semi-gelatinous layer. Sometimes its cells give rise to four ciliated zoospores, of two sizes, the 

 larger of which settle down and develop a cellulose coat; whilst of the further development of the smaller 

 nothing is known. The famous Red Snow (P. nivalis) of the arctic regions and Alps, which is also found 

 on stones in fresh- water streams, belongs to this genus, and is probably a rudimentary Palmella. 



IV. VoLVOCiNEiE. — Minute fresh-water Algce, consisting of a number of permanently 

 active zoospore-like bodies, associated in various forms, and surrounded by a gelatinous coat, 

 with or without an enveloping membrane. 



PRINCIPAL GENERA. 

 Volvox. Stephanospheera. Gonium. 



Volvox is a pale green globule, one-fiftieth of an inch in diameter, common in ponds, in constant 

 rolling motion. It consists of a membranous sac, studded with green points, and clothed with innumer- 

 able cilia. The green points consist of layers of zoospore-like bodies coating the inside of the sac, with 

 two cilia, which project through holes in the sac, and are further provided with delicate filaments, that 

 extend from their sides and meet similar filaments from the adjoining bodies. The zoospores are pyri- 



