^B. plumosa.^ Fronds branched twice or more; branchlets or pinnules tapering as they rise on the stalk, giving a triangular outline; stalk naked below; plants a vivid dark green in color, two to six inches long, growing in tufts on wharves and stones at low-water mark and in tide-pools. It is common along the whole Atlantic and Pacific coasts. It is well to use salt water for mounting this alga, since the green coloring-matter or granular endochrome with which it is filled easily escapes. (Plate VII.) GENUS ^Codium^ ^C. tomentosum.^ This is called the commonest seaweed in the world. It is abundant in every latitude, yet it does not appear on the eastern coast of North America. It is found on the gulf coast of Florida and is plentiful on the Pacific coast. The fronds are often a foot long, composed of closely packed, club-shaped branches dividing in a forking manner, and densely covered with fine filaments which give them a soft, sponge-like texture. (Plate VII.) ORDER =CAULERPACEÆ= GENUS ^Caulerpa^ (/From two Greek words meaning "stem" and "creep"/) /Caulerpa/ is the only genus of its order, but it contains about a hundred species, many of which resemble mosses, ferns, or cacti. Each plant is composed of a single cell, however much it may be [pg060] ramified. The frond consists of a prostrate stem, from the lower side of which root-like fibers or holdfasts descend into the hard sand or coral, and from the upper side leaf- and branch-like secondary fronds arise. These plants grow luxuriantly in tropical waters, extending over large surfaces, and are the chief food of turtles. (Plate VIII.) ^C. prolifera.^ Frond or lamina flat and leaf-like, two to four inches long, one half to three quarters of an inch wide, either simple or once forked; margin entire. Similar laminæ spring from the surface or from the edge or base of the different leaf-like portions. Laminæ rise from the upper side of the creeping, rooting stem. Its substance is somewhat horny and translucent. ^C. Mexicana.^ Prostrate, creeping stem, with rootlets or holdfasts below, and leaf-like fronds above; fronds simple or with one or two branches deeply cut in narrow lobes nearly to the center. The species abounds at Key West. (Plate VIII.) II OLIVE-GREEN AND BROWN SEAWEEDS (PHÆOPHYCEÆ) TABLE SHOWING THE CLASSIFICATION OF THE OLIVE-GREEN AND BROWN SEAWEEDS DESCRIBED IN THIS CHAPTER Class =ALGÆ= Subclass =Phæophyceæ= (/Olive-Green and Brown Seaweeds/) Orders Genera Species =ECTOCARPACEÆ= ^Ectocarpus^ ^E. littoralis^ ^E. siliculosus^ ^E. viridis^ ^E. tomentosus^ =SPHACELARIACEÆ= ^Sphacelaria^ ^S. cirrhosa^ ^S. radicans^ ^Cladostephus^ ^C. verticillatus^