A. echinatus. Resembles Enteromorpha in being tubular; compressed or inflated; obtuse at the apex; attenuated at the base. It differs from Enteromorpha in being olive in color, and in being covered with small oblong dots of darker shade. When the plant is young the dots are hairy. It grows in clusters, two to eighteen inches long, one half of an inch to one inch wide. Common along the New England coast.

P. fascia. Fronds light olive-green, leaf-like, three to six inches long, one fourth to one half of an inch wide; margin entire, slightly waved; contracted at base to short stalk; attached by disk. This species grows in bunches on rocks and stones at low-water mark, and is very common everywhere. (Plate X.)

D. viridis. Filaments cylindrical, about as thick as a bristle; branches opposite, in pairs, at intervals on the main stem. The branches branch again and continue to be disposed in the same manner. All are long and ultimately become very fine. The color is olive-green, becoming verdigris-green when exposed to the air for a short time or placed in fresh water. The species grows in deep tide-pools and below low-water mark, forming fine, feathery plumes, often a yard long, which give submerged rocks the appearance of a luxuriant garden. (Plate X.)

D. aculeata ("spiny"). Fronds cylindrical at base, flattened above; branches long and straight, arranged alternately, when young beset with pencils of fine hairs, often one half of an inch long, which, later, fall off, leaving alternate spines along the edges of the flattened branches. It [pg067] grows from one foot to six feet in length, below low-water mark, and is found washed ashore. It is an attractive plant in the spring, but is brown and coarse when old. Common everywhere. (Plate X.)

D. ligulata. Fronds two to six feet long, pinnate, having a flat main stem one half of an inch or more wide, with opposite flat branches; leaflets arranged along the edges of the branches, pointed at each end, and bordered with forward-pointing spines. It is found washed ashore, in abundance, in California, but is not found on the Atlantic coast. (Plate X.)

A. villosa. Olive-brown filaments, resembling fine, knotted threads, each knob having a whorl of delicate filaments. It grows from six inches to three feet long, in deep water. It is rare, but is occasionally found on the New England coast.

D. fœniculaceus. Fronds filiform, bristle-like, branching into delicate, hair-like branches; yellowish-brown. It resembles Chordaria flagelliformis, but is much finer. (Plate XI.)

C. flagelliformis ("whip-like"). Firm, leathery, somewhat elastic, slimy strings, six to twenty-four inches long, and twice as thick as a bristle; branches mostly undivided, short or long, irregularly placed on the main axis, and curving inward at the top of the frond; main axis not extending as far as the branches; blackish in color; attached by a disk to stones and shells; solitary or in bunches. It is common along the New England coast. (Plate XI.) [pg068]

M. virescens. Soft, slimy filaments, with branches and branchlets; olive-green. (Plate XI.)

M. divaricata. Fronds two to twenty-four inches high; branching irregularly, and generally without definite main axis; branches flexuous, solid at first, later hollow; branchlets short and wide-spreading. Common from Cape Cod southward; abundant in Long Island Sound. (Plate XI.)

C. filum. Entire frond cylindrical, divided internally by transverse septa; one fourth to one half of an inch in diameter, tapering at each end; ordinarily one to twelve feet long, but sometimes attaining a length of forty feet. When young the frond is covered with fine, transparent hairs; later it is brown and leather-like. The growth takes place at the base, just above the disk-like holdfast, and at the apex it is constantly dying off. The species is common on Northern shores, at and below low-water mark. Often it is in masses which seem like meadows of waving grass under water. Various small algæ and many zoöphytes are to be found on the fronds. (Plate XII.)

A. esculenta. Stem compressed, four to twelve inches long, one fourth to one half of an inch wide, and running like a midrib through the lamina; lamina one to ten feet long, two to ten inches wide, frequently torn and ragged; margin wavy; leaflets three to eight inches long and without midrib, growing on both sides of the stem, below the lamina. The spores are produced in the leaflets in the autumn. This is an edible alga and is used as food in Scotland and Ireland, where it is called henware, badderlocks, murlins, and so on. (Plate XII.)

A. Turneri. Stem two to twelve inches long, round below, flattened above, and extending like a midrib through the lamina; lamina one foot to four feet long, with holes over the whole surface; margin wavy. The perforations in the lamina are produced by conical hollow papillæ which cover the young frond and which at length burst, leaving a hole which enlarges as the plant expands. This species is found from Cape Cod to Greenland.

There are other species, which differ from this one in the size of the perforations, the shape of the lamina, and the prominence of the midrib. Harvey describes the plant as an arctic genus growing ten to twelve feet long. (Plate XII.) [pg070]

L. saccharina, the sea-tangle. This species differs from L. longicruris in having a short, solid stem and narrow, ribbon-like lamina. Stem three inches to four feet long; lamina three to thirty feet long, six to eighteen inches wide, with central band of depressed spots; margin much waved; color olive-green, semi-transparent. It is named from the saccharine matter, called mannite, which it contains. Found on northern shores of the Atlantic and the Pacific oceans. (Plate XII.)

L. digitata ("fingered"). Stem one to five feet long, thick, round, and solid; lamina oval at base, leathery, smooth, brown, deeply cleft into segments of unequal breadth. It is named from the hand-like form of the lamina. This species is found in Long Island Sound, but is not common south of Cape Cod. The stem is used by fishermen for knife-handles. Pieces of it, placed on the blades while green, contract in drying and become solid. (Plate XIII.)

D. fasciola. Fronds olive-brown, expanded, membranaceous, erect, flat; many times forked narrow branches; grows in tufts six to ten inches long, matted at the base.

D. dichotoma. Same as D. fasciola, except that the divisions of the forked frond are one eighth to one half of an inch wide. Found in tide-pools in Southern waters. (Plate XIII.)

Z. lobata. Thallus flat, fan-shaped, but not so rounded as in Padina pavonia, twelve or more inches in height, cleft irregularly into many [pg071] narrow lobes, the clefts extending nearly or quite to the base; olive-green, with concentric zones of darker color; edges thin and bordered with a dark line. Found in southern California and in tropical and subtropical seas.

T. atomaria. Spreading, fan-shaped frond; clefts irregular and not extending to the basal stem; spores arranged in dark wavy lines and spots on the frond, giving it a mottled appearance and beautiful gradation of color. Found in tropical seas. (Plate XIII.)

P. pavonia, the peacock's-tail. Frond broadly fan-shaped; substance between membranaceous and leathery; powdery on the outer surface; deeply and variously cleft or entire; several laminæ emanating from a stalk-like base; each lamina fan-shaped; concentric lines numerous; variegated in zones. This beautiful alga is always regarded as a prize. It is found on stones at low-water mark, and is not uncommon south of Charleston, South Carolina, but is more luxuriant in tropical seas. (Plate XIII.)

H. polypodioides. Fronds flat, forked, notched on lower part; divisions about one quarter of an inch wide; distinct midrib; olive-green; grows in tufts. It is found in North and South Carolina, and is abundant on the Florida Keys. (Plate XIV.)

C. multifida. Frond erect, flat; branches in a forking manner; ultimate branches fine and short, and with branchlets on the tips. This species resembles Taonia. It is found in Southern waters. (Plate XIV.)

H. lorea, the sea-thong. A cup-shaped base, from the center of which arises a flat, strap-like frond one fourth to one half of an inch wide and two to twenty feet long, branching dichotomously (or by forking), and dotted with pits, or conceptacles, in which the spores are formed. Found in the extreme North. [pg072]

F. vesiculosus. Midrib distinct through all the forked branches; margin entire, often wavy; air-vessels spherical or oblong, usually in pairs along the midrib; receptacles on terminal branches, which are swollen and filled with gelatinous matter, heart-shaped or forked, in oblong or pointed divisions; frond tough and leathery, often two feet long. (Plate XIV.)

F. serratus. Frond distinctly toothed or serrated along the margin; midrib conspicuous through the main axis and forked branchings; no air-vessels. This species is rare on the Atlantic coast. (Plate XV.)

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.)

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.)

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.)

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.

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.)

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.)

S. Montagnei. This species resembles S. vulgare, but is more slender in all its parts, and the receptacles are more elongated. From south of Cape Cod.

S. bacciferum. Particular interest attaches to this species from the fact that it is the one which forms the floating vegetation of the Sargasso Sea. It grows attached on the Florida Keys and in the West Indies. Specimens are sometimes carried by the currents northward, and are found washed ashore. It differs from S. vulgare in the leaves, which are thicker, more attenuated, and sharply toothed, and in having a greater number of air-vessels. A branch of this species brought from the Sargasso Sea had air-vessels so numerous and closely set that it resembled a bunch of small grapes.

N. multifidum. Frond six to twelve inches long, cylindrical, solid, cord-like, elastic, tough, shiny, very gelatinous; branches repeatedly in [pg080] a wide-forking manner; sometimes a branch will divide into several parts at the same point; color dark brown or purple. It is found, in summer only, from Long Island Sound northward, growing on smooth rocks which are exposed to the action of the waves.

S. furcellata. Frond cylindrical, one eighth of an inch in diameter, tapering at base, sometimes constricted at intervals, regularly and several times forked, ending in short divisions; branches of same length, giving a level top; two to four inches high; lake-red. When pressed the axis is visible, giving the appearance of a flat frond with a midrib. This species is found in summer only, washed ashore from Cape Cod southward and on the California coast. It is not common. (Plate XVII.)

G. corneum. Frond flat and horny, one inch to four inches high, narrow, erect, branched several times in the same plane; ultimate branchlets club-shaped, or swollen at the tips with masses of spores; color purple-red. It grows in tufts on mud-covered rocks, and on algæ at low-water mark. The typical form is found in Florida and on the Pacific coast. Smaller plants are found all along the Atlantic shore. It is an extremely variable plant, and is often difficult to distinguish on this account. (Plate XVII.)

C. crispus. Frond begins with flattened stem, which divides and subdivides many times in a broad-forked, fan-like manner; varies greatly in length and breadth of divisions, also in size and color, according to conditions of its habitation. In shallow tide-pools it is pale and [pg081] stunted; but under the shelter of rocks, in deep water, it grows in dense masses and is a dark purplish-red or reddish-green. Often it appears iridescent when seen through the water, with the sun shining on it. It is firm and leathery in substance. It is an edible alga, and was formerly very generally used for culinary purposes. At Hingham, Massachusetts, large quantities are gathered as an article of commerce. It is a beautiful and very common plant found from New York northward. (Plate XVII.)

G. mamillosa. Frond three to six inches high, one inch to two inches broad, flat, leathery, gelatinous; forking near the base, then dividing and subdividing in the same plane; segments more or less wedge-shaped and with a tendency to roll inward; covered with numerous small nipple-like protuberances which contain the spores. These projections distinguish this genus from Chondrus, which it otherwise resembles, and with which it grows. The color is dark purple. It is found from Boston northward. (Plate XVIII.)

G. radula. Frond flat and thick; rising from a short stem and widening to several inches; sometimes tapering to the top, sometimes blunt or divided, sometimes cleft on the sides, but usually simple; covered with wart-like projections; color dark, livid red. It is found on the Pacific coast at all seasons, growing on rocks between tide-marks. Large specimens are one foot to three feet long and six to ten inches wide. (Plate XVIII.)

G. spinosa ("thorny"). Frond thick, leathery; surface rough and spiny; form variable, the divisions sometimes emanating from a broad, flattened base, or again branching from a main axis; all covered with the protruding processes peculiar to the genus; color dark red, brown, or purple. It is found on the California coast. (Plate XVIII.)

G. microphylla ("small-leaved"). Plant rises from short, flat stem, and rapidly expands into a flat, wide, thin frond which is simple or divided into two or three segments, each of which tapers into a long, pointed apex; thickly covered with long, slender spines, and on its edges bearing small, thin leaflets; color brownish-red. It is abundant on the California coast. (Plate XVIII.)