^F. furcatus.^ Frond narrow, tough, without air-vessels; regular forked branching; midrib distinct below, inconspicuous above; receptacles long, narrow, not inflated. Found from Boston northward. ^F. ceranoides.^ Frond flat, rather membranaceous, or less leathery than in the preceding species; repeatedly forked; midrib not running through every division; no air-vessels. (Plate XV.) GENUS ^Ascophyllum^ ^A. nodosum.^ This species, formerly called /Fucus nodosus/, is next to /Fucus vesiculosus/ the most common rockweed. Frond one to five feet long, dark brown, strap-like, leathery; width of main stems one fourth of an inch or more, and uniform throughout; large, single, oblong air-vessels distend the frond at intervals. Branches of various length emerge from the sides of the main stem. Ovoid or ellipsoidal branchlets or receptacles, single or in groups, occur at intervals along the sides of both stem and branches. These fall off after a time and are found in quantities in tide-pools. (Plate XV.) GENUS ^Phyllospora^ ^P. Menziesii.^ Branching holdfast; short stem which immediately divides into strap-like branches; branches edged with leaves varying in length, rounded at top, narrow, stalked at base; leaves placed at intervals, or crowded together, and interspersed with air-vessels which are often tipped with leaflets; stems expand at summit into leaf-like laminæ and are edged with leaflets at the base; plant often one hundred and twenty feet or more in length; tough and leathery in substance. Very common on the California coast. (Plate XVI.) GENUS ^Cystoseira^ ^C. expansa.^ Frond long, slender, repeatedly branched; air-vessels ellipsoidal and "chained" together in the lower half of the branches. The plant grows in deep water, ad shows iridescent colors when seen through the water. It is found on the California coast. GENUS ^Halidrys^ ^H. osmunda^, the sea-oak. Frond flat, alternately toothed or indented below; branched apex, bearing air-vessels like long-stalked pods; substance leathery. Found on the coast of southern California. (Plate XVI.) GENUS ^Sargassum^ ^Sargassum^ is distinguished by its differentiation into stem and leaf, resembling in outward appearance the higher plants. It [pg074] is a tropical and subtropical genus, and has one hundred and fifty species. Two of these, /S. vulgare/ and /S. Montagnei/, are found as far north as Cape Cod. See Introduction, page 34. ^S. vulgare.^ Stems cylindrical; branches alternate; leaves long, narrow, toothed, with short stalk and midrib; minute dark spots on its surface; air-vessels small balls resembling berries set on stalks and usually tipped with a long point; receptacles small, twig-like forms in the axils of the leaves; color olive-brown; plant one foot to three or more feet long. Common in Long Island Sound. (Plate XVI.)