predominance of filamentous and encrusting, often inconspicuous, forms, exhibiting a bluish-green colour when examined under the microscope; (b) a zone from near high-water mark to half-tide level, occupied chiefly by algae of a bright grass-green tint; (c) from half-tide level to low-tide mark, where the majority of the plants are olive-brown in colour; and finally (d) from near low-water mark to depths never exposed by the lowest ebb, where the preponderance of forms are of a distinctly red colour. Although not a few shores exhibit these zones fairly clearly, it must be remembered that, owing to the nature of the shore, the character of the tides, and the absence or presence of large influxes of fresh water, the zoning is not always clearly defined. For instance, the uppermost zone of blue-green forms is most likely to be met with on low-lying coast-lines where the seashore proper merges gradually into brackish marshes and muddy pools, such as, for example, the estuaries of the Dee and Mersey, or of the Clyde near Dumbarton. Grass-green forms are most plentiful on shelving rocky shores; whilst on such steep rocky shores as those of the fjords of the west coast of Scotland olive-brown seaweeds form the prevailing vegetation right up to high-water mark. It must be also borne in mind that certain species of algæ are invariably found in regions of the littoral area not characteristically occupied by the majority of forms of a similar hue. Thus the common dwarf species, Pelvetia canaliculata, closely allied to the familiar bladder-wrack (Fucus vesiculosus), belongs to the olive division of seaweeds, and yet is invariably found at or even above high-water mark. Tangle (Laminaria digitata), also an olive seaweed, is, on the other hand, a deep-water form only exposed at low tides, whilst the genus Struvea, one of the pure-green algae, may be dredged from 30 fathoms. Very many red alga are found under cover of the olive forms between tide marks, whilst some have their habitat at or above high-water mark. For example, two species of the genus Rhodochorton form a crimson velvety pile on rocks from half-tide level to far above highwater mark, and another and easily recognisable form, Catenella opuntia, grows on the lee side of rocks which are seldom touched by the flood-tide.

It is worthy of note that the classification of seaweeds into four groups according to colour is strikingly supported by the morphology and lifehistory of the forms so brought together. This fact becomes all the more remarkable when it is remembered that colour among higher plants is in very few cases of even specific value in classifica

287

tion. The blue-green algae are known as Cyanophyceae, the pure-green as Chlorophyceae, the olive as Phæophyceae, and the red as Rhodophyceæ. (By some authors the lower members of the first two groups are classed together under the name of Protophyceae.) All possess the green colouring matter chlorophyll, but in the blue, olive, and red forms additional colouring matters (phycocyanin, phycophæin, and phycoerythrin) are present to a greater or less extent, masking the pure-green tint so well seen in the Chlorophyceae. It is impossible in the present state of our knowledge to dogmatise on the precise value of these additional pigments, but we cannot be far wrong in saying that they are associated with the modification of the intensity or quality of sunlight, and aid or protect the chlorophyll in the peculiar and vitally important duties which it performs in the nutrition of the organism (see CHLOROPHYLL). It has been ascertained that certain rays of the solar spectrum are more efficient than others in the work of assimilation, and it is worthy of note that these rays are precisely those which are first intercepted in the passage of sunlight into sea-water. Our ignorance of the important physiological problems involved may be estimated when we place against this explanation the fact that Kjellman in his exploration of the flora of the Arctic Sea found that alga grew and reproduced at a mean temperature of 1° C. and during the long and dark arctic night of three months' duration.

Turning from the bathymetric distribution of seaweeds to their surface distribution, we find here also many interesting and difficult problems. In the first place the medium in which seaweeds live is of a more uniform temperature than that to which land plants are exposed, although against this we must place the fact that seaweeds are more susceptible to fluctuations of temperature. Whilst ocean currents are undoubtedly the chief agents in the transport of the marine flora, long tracts of deep ocean must prove serious barriers to the migration of littoral species. It is scarcely necessary to point out that continental areas, hotter and colder regions of the sea, and long stretches of sandy shore must also act as barriers to possible migration. The effects of such barriers are well seen in comparing the floras of the tropical Atlantic and of the Indian Ocean, the north and south temperate Atlantic, and the eastern and western shores of the same great ocean. From the following table (abstracted from Murray's paper on the 'Distribution of Marine Algæ,' Trans. Biol. Soc. Liverpool, vol. v. p. 164) it will be seen that,

taking three principal regions into consideration, the Arctic marine flora consists of 259 species belonging to 111 genera, the West Indian region possesses 788 species and 150 genera, the Australian 1132 species in 255 genera, and that nevertheless only 17 genera and 5 species of Rhodophyceae, 6 genera and 1 species of Phæophyceæ, 5 genera and 6 species of Chlorophyceæ, and 4 genera and no species of Protophyceae are common to all.

The structure, life-history, and classification of the lower alga (both fresh-water and marine) having been dealt with in the article Algæ (q.v.),

there is left for treatment the two higher groupsviz. Phæophyceae and Rhodophyceae. It will be most in accordance with the aim of the present article to sketch very briefly the main lines of classification, and to select a few typical examples for more detailed notice.

The Phæophyceæ include all the olive-brown seaweeds found on our shores, and are subdivided according to their methods of reproduction into three chief series-viz. (a) the Phæosporeæ, represented by such forms as Ectocarpus, Cutleria, Sphacelaria, and the giants among seaweeds,

Laminaria, Macrocystis, and Lessonia; (b) the Fucaceae.g. Fucus, Ascophyllum, Pelvetia, &c.; and (c) the Dictyotaceae-e.g. Dictyota and Padina. The members of the Phæosporeæ have a most

Fig. 1.-Ectocarpus confervoides : A portion of the thallus with multilocular sporangia (x 10). varied vegetative form. Many are filamentous and branched, such as Ectocarpus and Sphacelaria, some are tubular and unbranched, as Asperococcus and Scytosiphon, or tubular and branched-Chordaria. Others are ribbon-shaped-e.g. Cutleria; not a few are membranous and encrusting-e.g. Ralfsia; whilst Laminaria forms large expanded leathery-stalked fronds. In histological differentiation several types may be distinguished. In Ectocarpus the fronds consist of branched filaments of cylindrical cells, whilst in other genera the fronds are composed of elongated central cells surrounded by smaller cortical cells. In the Laminariacea the medullary portion of the thallus contains elongated branched tubular cells which show a marked resemblance to the sieve tubes of Phanerogams, whilst the small cortical cells exhibit that intercommunication of protoplasm which is of so great physiological importance in the higher plants. Both sexual and asexual methods of reproduction are known to occur, though not as yet in all genera. Vegetative propagation by gemmæ is also not uncommon. The asexual reproductive organs are in the form of unilocular sporangia, the contents of which are transformed into zoo

Fig. 2.-Laminariaceæ : A, Laminaria digitata, var. stenophylla; B, C, L. digitata, var. cloustoni; D, young form of B (all much reduced). (After Luerssen.)

spores, small motile cells furnished with two flagella each, and capable after a period of activity of longer or shorter duration of settling down and forming new plants. The sporangia either are de veloped externally on the thallus or are the terminal cells of short branches. They are frequently collected in groups (sori), and are accompanied by sterile filaments. The sexual organs are multilocular sporangia (gametangia), of diverse form, each loculus giving rise to a single motile cell somewhat like a zoospore. These cells conjugate in pairs, the product (zygote) behaving in a precisely similar manner to the zoospore. Although in most of the Phæosporeæ the zoogametes are morphologically indistinguishable, interesting gradations may be observed in some genera where the zoogametes are differentiated into

male and female cells. Cutleria is especially interesting in this respect, as the female gametes are much larger than the male gametes, and come to rest before conjugation with the still motile male cell.

The Fucaceæ are characterised by having distinctly differentiated sexual organs with nonmotile ova and motile fertilising

cells. The ova are Fig. 3.-Fucus platycarpus : formed within the A portion of the thallus show. swollen cells (oogo- ing receptacles (x 1). (After nia) which arise from Thuret.) the wall of flaskshaped cavities (conceptacles), and are accompanied by unbranched hairs. The fertilising cells, antherozoids or sperms, are produced in ovoid terminal cells of branched hairs (antheridia), which likewise arise from the walls of similar conceptacles. In Fucus platycarpus both ova and sperms are formed in the same conceptacle; in most Fucaceæ, however, they are formed on different plants. Asexual

SEAWEEDS

The Dictyotaceae are an aberrant group of Phaophyceae with distinct affinities to the Rhodophyceae. They resemble that group in having non-motile spores produced in fours in sporangia which are clustered in sori over the surface of the frond (Dictyota) or along the midrib. The sexual organs are in the form of antheridia and oogonia. The male organs produce non-motile fertilising cells resembling the pollinoids of the Rhodophyceae, though Johnson (Jour. Linn. Soc. Bot., vol. xxvii. p. 467) considers that possibly the pollinoids of Dictyopteris may be ciliated like those of Cutleria. The oogonia are arranged in sori, each containing one ovum. In both Fucaceæ and Dictyotaceæ fertilisation is external.

The Rhodophyceae (Floride) form a very large assemblage of most varied vegetative form, and every possible shade of red from a purple black to brilliant pink. The root may be a branched mass, a plate, or a disc attached to mud, other algae, or rock, whilst the fronds are filamentous, membranous, crustaceous, or calcareous. The asexual organs consist of sporangia whose entire contents in some genera escape as a single nonmotile spore. In the majority, however, each sporangium contains four non-motile spores. The sporangia are solitary or grouped in sori, and often sunk in the tissue of the frond or in special branches. The sexual organs are antheridia and procarpia. The antheridia are generally modified terminal branches or special areas in the thallus (of the more succulent forms), from which are derived short rodlike fertilising cells, here called pollinoids. The female organ is a procarp, whose structure varies in complexity in the different orders of Rhodophyceæ. In the simplest condition it recalls

Fig. 5.-Griffithsia setacea (one-half natural size). (After Thuret.)

ducts of fertilisation. Fertilisation is effected by fusion of a pollinoid with the trichogyne, the immediate result being the formation of a cluster of cells, the carpospores, derived from the fertile cells of the base. These carpospores may form a mulberry-like mass (Nemalion), or be enclosed by a loose involucre of filaments (Griffithsia), or by an ovoid capsular investment with a termínal pore (Polysiphonia). In others again the collection of carpospores (cystocarp) is completely enclosed within a thickwalled spherical sac (Plocamium), or may be sunk in the tissue of the frond (Dumontia). The Rhodophycea embrace a large number of orders, the representatives of several of which form wellknown objects of interest on the seashore. The best known Fig. 7.- Corallina of these perhaps are Carrageen (Chondrus crispus), Dulse

officinalis, a calcareous seaweed (natural size).

Rhodymenia palmata), and Laver (Porphyra laciniata). The genera Callithamnion, Delesseria, Nitophyllum, Plocamium, and Odonthalia are well known to collectors for the beauty of their fronds. concluding this article it may be of interest to point out that the vast collection of feathery plant-like

α

In

Fig. 6.-Odonthalia dentata (one-third natural size). the female organ of Coleochate, and consists of a rounded cell with a long filamentous apical portion, the trichogyne. In higher members of the series the trichogyne is separated from that portion of the procarp from which the products of fertilisation (carpospores) are derived by one or more intermediate cells, the trichophore, and the basal part itself may become multicellular, all or only some of the cells of which produce the pro

Fig. 8.-Reproductive Organs of the Rhodophyceae: a, cystocarp of Spermothamnion turneri; b, cystocarp of Polysiphonia urceolata; c, cystocarp and antheridium of Catenella opuntia; d, tetrasporangia of Callithamnion tenuissimum.

forms, popularly classed as 'seaweeds' by seaside visitors and sold as such after being fancifully tinted, are in no respect related to the forms we have been considering, but really belong to the zoophyte division (Hydrozoa) of the animal kingdom.

For British Seaweeds, see Harvey, Phycologia Britannica; Gray, British Seaweeds; Landsborough, Popular History of British Seaweeds. General and Systematic: Agardh, Species, Genera, et Ordines Algarum; Thuret, Etudes Phycologiques; Bornet et Thuret, Notes Algologiques; Hauck, Die Meeresalgen; Reinke, Atlas Meeresalgen; Falkenberg in Schenk's Handbuch der Botanik; Schmitz, Untersuchungen über die Befruchtung der

Florideen.

Sea-wolf. See WOLF-FISH.

Sebastian, king of Portugal (q.v.), a grandson of the Emperor Charles V., perished at the fight of Alcazar in Algeria, warring against the Moors, on 4th August 1578. Soon after the battle doubt was thrown upon his death, and impostors, pretending to be the chivalrous young king, began to crop up -first (in 1584) an adventurer, the son of a poor Portuguese potter, who was nicknamed, half in derision, half in raillery, the King of Penamacor; then came Matheus Álvares, a sort of brigandinsurgent; then in 1594 a Spanish cook of Madrigal in Castile. None of these people were taken seriously. A fourth impostor found more credence, one Marco Tullio Catizzone, a Calabrian, who first made his pretensions known at Venice in 1598. He was hanged at San Lucar in Spain in September 1603. The strongest support of these successive impostors was the undying belief of the common people of Portugal that their popular hero, Sebastian, would some day reappear. The belief grew particularly strong in 1807-8 during the French occupation of Portugal. And even so late as 1838 it was used as a rallying-cry by a party of insurrectionists amongst the Portuguese Brazilians. See M. D'Antas, Les faux Don Sébastien (1866). Sebastian, ST, a martyr of the early church,

was a native of Narbonne. Under Diocletian he

became a captain of the prætorian guard, and secretly a Christian. It coming to the ears of Diocletian how Sebastian personally encouraged those who were being led out to death for being Christians, the emperor had his captain tied to a stake and shot to death by archers. But they did not wholly kill him; a pious woman, Irene by name, took him away, and tended his wounds. As soon as he was recovered Sebastian boldly faced the tyrant, and upbraided him for his cruelty. Diocletian then ordered him to be beaten to death (288) with rods. He is a protector against plague

and pestilence, and is specially honoured on 20th January. His first martyrdom-a young and handsome soldier bristling with arrows-was favourite subject for the Italian religious painters, as Mantegna, Veronese, and Domenichino.

a

Sebastiani, FRANÇOIS HORACE BASTIEN, COUNT, marshal of France, was born November 10, 1772, at Porta d'Ampugnano, a village near Bastia, in Corsica. Entering the French army in 1789, he became one of Napoleon's most devoted partisans, and advanced rapidly. He fought at Marengo, executed some important diplomatic service in Turkey in 1802-3, after which he became general of brigade, and was wounded at Austerlitz. In 1806 he was again deputed to Turkey, this time to break the alliance of the Porte with Russia and England. His mission was successful, and Turkey declared war upon the allies. Thereupon the English fleet forced a passage through the Dardanelles, and cast anchor before Constantinople. Sebastiani, however, speedily put the coast batteries in a state fit for action, and got several small gunboats afloat. But the deposition of the sultan and the treaty of Tilsit put an end to the French intrigues in Turkey, and Sebastiani was recalled (June 1807). He subsequently commanded the fourth French army corps in Spain, and distinguished himself in the Russian campaign of 1812 and at Leipzig. On the exile of Napoleon to Elba he gave in his adherence to the Bourbon government, but joined his old master on his return. After the revolution of 1830 he held for brief periods the portfolios of naval and foreign affairs, and the embassies to Naples and London, but was more distinguished for his elegance and graceful demeanour in the Parisian salons than as a politician or administrator. He was made a marshal of France in 1840, and died at Paris, July 20, 1851.

SEBASTOPOL

Sebastiano del Piombo, Italian painter, whose family name was LUCIANI, and who got his nickname Of the Seal' (Piombo) because at the accession of his patron, Giulio de' Medici, as pope (Clement VII.) in 1523 he was given the office of sealer of papal briefs. He was born at Venice in 1485, and learned the art of painting from Giovanni Bellini and Giorgione. After painting a St Chrys ostom for the church of that saint in Venice, Sebastiano was taken to Rome by Agostino Chigi (q.v.) about 1512. He helped to decorate Chigi's palace of Farnesina with frescoes illustrating clas sical mythology, and by his excellence as a colourist won the esteem and friendship of Michelangelo. The two seem then to have worked in conjunction, Sebastiano carrying out in colour designs and drawings made by Michelangelo. Amongst the fruits of this artistic partnership three pictures at least are of the highest rank-viz. The Raising of Lazarus' (in the London National Gallery), and a couple of scenes from the last days of Christ (in the church of St Peter in Montorio at Rome). Sebastiano, who possessed no great powers of invention, excelled also as a portrait-painter. The best specimens of his skill in this particular line Doria, two members of the Colonna family, Sebasembrace portraits of Pope Clement VII., Andrea Agatha. An indolent man and a dilatory, Sebastiano himself, Cardinal Pole, and a lady as St tiano did little painting after his appointment as papal seal-keeper; yet he invented a method of painting on slate and stone. He died at Rome in

1547.

port and fortress, is situated near the south-west Sebastopol, or SEVASTOPOL, a Russian seaextremity of the Crimea, on the southern side of one of the finest natural harbours in the world, 43 miles long from east to west and mile across. The place is celebrated for the long siege of the The allies during the Crimean war of 1854-55. town and harbour were defended by several forts and batteries, mounted by 700 guns in all, some of heavy calibre. The forts were of immense strength, built of limestone faced with granite, on which artillery was found to make but little impression. On the land side, with the exception of a slight loopholed wall extending partially round the western side, the town, previous to the siege, was entirely undefended; but the earthworks and fortifications then successively extemporised by the genius of General Todleben kept the armies of France and England at bay for eleven months, from October 1854 to September 1855. The place sustained repeated bombardments until the capture of the Malakoff and Redan works, on September 8, 1855, at length forced the Russians to evacuate the lines and retire to the north side. The town was completely ruined; the docks and forts still standing were blown up by French and English engineers, and by the treaty of Paris (1856) were not to be restored; but the restrictions were removed by the abrogation of the neutrality of the Black Sea by the Conference of London (1871). Since the siege the town has been in great part rebuilt, but at first grew slowly. However, since 1885 the Russian government have been actively restoring the fortifications and reconstructing the docks, it having been decided that Sebastopol was to be reserved entirely for the imperial navy, and a new commercial port to be built on a bay 2 miles south-west of the town or else at Theodosia. The trade fluctuates greatly, the imports between £134,660 (1890)-chiefly for cotton and coal-and £653,210 (1887), and the exports between £1,315,600 (1890) and £3,072,560 (1889), all for grain. Pop. (1890) 29,000, exclusive of a garrison of 12,000. Sebastopol was founded on the site of a Tartar village inimediately after the Russian conquest of the