Page:Encyclopædia Britannica, Ninth Edition, v. 18.djvu/468

 446 P E A P E A antiquity. Traces of it have been found in the Swiss lake- dwellings ; it is mentioned in the oldest Greek writings, and was cultivated by the Romans. The word &quot;pear&quot; or its equivalent occurs in all the Celtic languages, while in Slavonic and other dialects different appellations, but still referring to the same thing, are found, a diversity and multiplicity of nomenclature which leads De Candolle to infer a very ancient cultivation of the tree from the shores of the Caspian to those of the Atlantic. A certain race of pears, with white down on the under surface of their leaves, is supposed to have originated from P. nivalis, and their fruit is chiefly used in France in the manufacture of PERRY (q.v.). Other small-fruited pears, distinguished by their precocity and apple-like fruit, may be referred to P. cordata, a species found wild in western France, and in Devonshire and Cornwall. The late Professor Karl Koch considered that cultivated pears were the descendants of three species P. pcrsica (from which the bergamots have descended), P. clasagrifolia, and P. sincnsis. De- caisne, who made the subject one of critical study for a number of years, and not only investigated the wild forms, but carefully studied the peculiarities of the numerous varieties cultivated in the Jardin des Plantes, refers all cultivated pears to one species, the individuals of which have in course of time diverged in various directions, so as to form now six races : (1) the Celtic, including P. cordata ; (2) the Germanic, including P. communis, P. Achras, and P. pirnster ; (3) the Hellenic, including P. parviflora, P. sinaica, and others ; (4) the Pontic, including P. elieagrifolia ; (5) the Indian, comprising P. Pasch& ; and (6) the Mongolic, represented by P. sincnsis. With reference to the Celtic race, P. cordata, it is interesting to note its connexion with Arthurian legend, and the Isle of Avalon or Isle of Apples. An island in Loch Awe has a Celtic legend containing the principal features of Arthurian story ; but in this case the word is &quot;berries&quot; instead of &quot;apples.&quot; Dr Phene visited Armorica (Brittany) with a view of investigating these matters, and brought thence fruits of a small berry-like pear, which were identified by the writer with the Pyrus cordata of western France, as well as with a tree which had then been recently discovered in some parts of Devonshire and Cornwall by Mr Briggs. (For cultivation of pears see HORTICULTURE, vol. xii. p. 274.) PEARL. Pearls are calcareous concretions of peculiar lustre, produced by certain molluscs, and valued as objects of personal ornament. It is believed that most pearls are formed by the intrusion of some foreign substance between the mantle of the mollusc and its shell, which, becoming a source of irritation, determines the deposition of nacreous matter in concentric layers until the substance is com pletely encysted. The popular notion that the disturbing object is commonly a grain of sand seems untenable ; according to Dr Gwyn Jeffreys and some other concho- logists, it is in most cases a minute parasite ; while Dr Kelaart has suggested that it may be the frustule of a diatom, or even one of the ova of the pearl -producing mollusc itself. The experience of pearl-fishers shows that those shells which are irregular in shape and stunted in growth, or which bear excrescences, or are honeycombed by boring parasites, are those most likely to yield pearls. The substance of a pearl is essentially the same as that which lines the interior of many shells, and is known as &quot; mother-of-pearl.&quot; Sir D. Brewster first showed that the iridescence of this substance was an optical phenomenon due to the interference of rays of light reflected from micro scopic corrugations of the surface an effect which may be imitated by artificial striations on a suitable medium. When the inner laminated portion of a nacreous shell is digested in acid the calcareous layers are dissolved away, leaving a very delicate membranous pellicle, which, as shown by Dr Carpenter, may retain the iridescence as long as it is undisturbed, but which loses it when pressed or stretched. Although a large number of molluscs secrete MOTHER- OF-PEARL (y.v.), only a few of them yield true pearls. The finest are obtained from the so-called &quot; pearl oyster,&quot; the Avicula (Meleagrina) maryaritifera, Linnaeus, while fresh water pearls are procured chiefly from the &quot;pearl mussel,&quot; Unto (Margaritana) margaritiferw, L. 1 These river-pearls are generally of dull leaden hue, and inferior in beauty to those of marine origin. It is obvious that if a pearl presents a perfectly spheri cal form it must have remained loose in the substance of the muscles or other soft tissues of the mollusc. Fre quently, however, the pearl becomes cemented to the in terior of the shell, the point of attachment thus interfering with its symmetry. In this position it may receive suc cessive nacreous deposits, which ultimately form a pearl of hemispherical shape, so that when cut from the shell it may be flat on one side and convex on the other, forming what jewellers know as a &quot;perle bouton.&quot; In the course of growth the pearl may become involved in the general de posit of mother-of-pearl, and be ultimately buried in the substance of the shell. It has thus happened that fine pearls have occasionally been unexpectedly brought to light in cutting up mother-of-pearl in the workshop. When a pearl oyster is attacked by a boring parasite the mollusc protects itself by depositing nacreous matter at the point of invasion, thus forming a hollow body of irregular shape known as a &quot;blister pearl.&quot; Hollow warty pearl is sometimes termed in trade &quot; coq de perle.&quot; Solid pearls of irregular form are often produced by deposition on rough objects, such as small fragments of wood, and these, and in fact all irregular-shaped pearls, are termed &quot; perles baroques,&quot; or &quot;barrok pearls.&quot; It appears that the Romans in the period of the Decline restricted the name unio to the globular pearl, and termed the baroque margaritum. It was fashionable in the 16th and 17th centuries to mount curiously -shaped baroques in gold and enamel so as to form ornamental objects of grotesque character. A valuable collection of such mounted pearls by Dinglinger is preserved in the Green vaults at Dresden. A pearl of the first Avater should possess, in jewellers language, a perfect &quot;skin&quot; and a fine &quot;orient&quot;; that is to say, it must be of delicate texture, free from speck or flaw, and of clear almost translucent white colour, with a subdued iridescent sheen. It should also be perfectly spherical, or, if not, of a symmetrical pear-shape. On re moving the outer layer of a pearl the subjacent surface is generally dull, like a dead fish-eye, but it occasionally happens that a poor pearl encloses a &quot;lively kernel,&quot; and may therefore be improved by careful peeling. The most perfect pearl in existence is said to be one, known as &quot; La Pellegrina,&quot; in the museum of Zosima in Moscow ; it is a perfectly globular Indian pearl of singular beauty, weigh ing 28 carats. The largest known pearl is one of irregu lar shape in Mr Beresford Hope s collection at the South Kensington museum. This magnificent pearl weighs 3 oz., has a circumference of 4^ inches, and is surmounted by an enamelled and jewelled gold crown, forming a pendant of great value. Pearl Fisheries. The ancients obtained their pearls chiefly from India and the Persian Gulf, but at the present time they are also procured from the Sulu seas, the coast of Australia, the shores of Central America, and some of the South Pacific islands. The ancient fisheries of Ceylon (Taprobane) are situated in the Gulf of Manaar, the fishing- 1 Meleagrina maryaritifera, L., belongs to the family Aviculidfe of most zoologists, to the family Avicidacete, order Monomya, of article MOLLUSCA. Meleagrina is merely a sub-genus of Avicula. The animal which produces fresh-water pearls in Britain and other parts of Europe was named Unio msiryaritiferus by Retzius in Nova Gen. Test., and this is the name adopted by most modern zoologists ; the animal was placed in a separate genus, Margarititna, by Schumacher for insuffi cient reasons. It belongs to the order Isomya, family Unionaccie. The molluscs from which river-pearls are obtained in the United States and other parts of the world are mostly species of Unio or Anodonta. The above are all Lamellibranchs.