512 P P P P while in Kamchatka it is sometimes ground up and mixed with meal ; the gum secreted by the buds was employed by the old herbalists for various medicinal purposes, but is probably nearly inert ; the cotton-like down of the seed has been converted into a kind of vegetable felt, and has also been used in paper-making. A closely related form is the well-known Lombardy Poplar, P. fastigiata, remark able for its tall cypress-like shape, caused by the nearly vertical growth of the branches. Probably a mere variety of the black poplar, its native land appears to have been Persia or some neighbouring country ; it was unknown in Italy in the days of Pliny, while from remote times it has been an inhabitant of Kashmir, the Punjab, and Persia, where it is often planted along roadsides for the purpose of shade ; it was probably brought from these countries to southern Europe, and derives its popular name from its abundance along the banks of the Po and other rivers of Lombardy, where it is said now to spring up naturally from seed, like the indigenous black poplar. It was introduced into France in 1749, and appears to have been grown in Germany and Britain soon after the middle of the last century, if not earlier. The Lombardy poplar is valuable chiefly as an ornamental tree, its timber being of very inferior quality ; its tall erect growth renders it use ful to the landscape-gardener as a relief to the rounded forms of other trees, or in contrast to the horizontal lines of the lake or river-bank where it delights to grow. In Lombardy and France tall hedges are sometimes formed of this poplar for shelter or shade, while in the suburban parks of Britain it is serviceable as a screen for hiding buildings or other unsightly objects from view ; its growth is extremely rapid, and it often attains a height of 100 feet and upwards, while from 70 to 80 feet is an ordinary size in favourable situations. P. canndensis, the "Cotton-wood" of the western prairies, and its varieties are perhaps the most useful trees of the genus, often forming almost the only arborescent vegetation on the great American plains. The P. canadcnsis of Michaux, which may be regarded as the type of this group, is a tree of rather large growth, with rugged grey trunk, and with the shoots or young branches more or less angular ; the glossy deltoid leaves are sharply pointed, somewhat cordate at the base, and with flattened petioles ; the fertile catkins ripen about the middle of June, when their opening capsules discharge the cottony seeds which have given the tree its common western name ; in New England it is sometimes called the " River Poplar." The cotton-wood timber, though soft and perish able, is of value in its prairie habitats, where it is frequently the only available wood either for carpentry or fuel ; it has been planted to a considerable extent in some parts of Europe, but in England a kindred form, P. monilifera, is generally preferred from its larger and more rapid growth. In this well-known variety the young shoots are but slightly angled, and the branches in the second year become round ; the deltoid short-pointed leaves are usually straight or even rounded at the base, but sometimes are slightly cordate ; the capsules ripen in Britain about the middle of May. This tree is of extremely rapid growth, and has been known to attain a height of 70 feet in sixteen years ; the trunk occasionally acquires a dia meter of from 3 to 5 feet, and, according to Emerson, a tree near New Ashford, Massachusetts, measured 20 feet 5 inches in circum ference ; it succeeds best in deep loamy soil, but will flourish in nearly any moist but well-drained situation. The timber is much used in some rural districts for flooring, and is durable for indoor pur poses when protected from dry-rot ; it has, like most poplar woods, the property of resisting fire better than other timber. The native country of this sub-species has been much disputed ; but, though still known in many British nurseries as the " Black Italian Pop lar," it is now well ascertained to be an indigenous tree in many parts of Canada and the States, and is probably a mere variety of P. canadensis ; it seems to have been first brought to England from Canada in 1772. In America it seldom attains the large size it often acquires in England, and it is there of less rapid growth than the prevailing fonn of the western plains ; the name of " cotton - wood" is locally given to other species. P. macmphylla or candi- cans, commonly known as the Ontario Poplar, is remarkable for its very large heart-shaped leaves, sometimes 10 inches long ; it is found in New England and the milder parts of Canada, and is frequently planted in Britain ; its growth is extremely rapid in moist land ; the buds are covered with a balsamic secretion. The true Balsam Poplar, or Tacamahac, P. balsamifera, abundant in most, parts of Canada and the northern States, is a tree of rather large growth, often of somewhat fastigiate habit, with round shoots and oblong-ovate sharp-pointed leaves, the base never cordate, the petioles round, and the disk deep glossy green above but somewhat downy below. This tree, the " Hard " of the Canadian voyageur, abounds on many of the river sides of the north-western plains ; it occurs in the neighbourhood of the Great Slave Lake and along the Mackenzie river, and forms much of the drift-wood of the Arctic coast. In these northern habitats it attains a large size ; the wood is very soft ; the buds yield a gum-like balsam, from which the common name is derived ; considered valuable as an antiscorbutic, this is said also to have diuretic properties ; it was formerly imported into Europe in small quantities, under the name of " baume focot," being scraped off in the spring and put into shells. This balsam gives the tree a fragrant odour when the leaves are unfolding. The tree grows well in Britain, and acquires occasion ally a considerable size. A very closely allied variety abounds in Siberia and Dauria, chiefly distinguished by its wider leaves, rounded growth, and the darker tint of its wood ; a kind of wine, esteemed as a diuretic, is prepared in Siberia from the buds. Its fragrant shoots and the fine yellow green of the young leaves recommend it to the ornamental planter. It is said by Aiton to have been intro duced into Britain about the end of the 17th century. (C. P. J. ) POPLIN, or TABINET, is a mixed textile fabric consist ing of a silk warp with a weft of worsted yarn. As the w r eft is in the form of a stout cord, the fabric has a ridged structure, like rep, which gives depth and softness to the lustre of the silky surface. Poplins are used for dress purposes, and for rich upholstery work. The manufacture is of French origin ; but it was brought to England by the Huguenots, and has long been specially associated with Ireland. The French manufacturers distinguish between popelines tinies or plain poplins and popelines a dispositions or Ecossaises, equivalent to Scotch tartans, in both of which a large trade is done with the United States from Lyons, POPOCATEPETL (Aztec popocani, "smoking," tepetl, "mountain"), a burning mountain in Mexico, in 18 59 47" N. lat. and 98 33 1" W. long., which along with the neighbouring and somewhat lower summit of Ixtaccihuatl (Aztec " White Woman ") forms the south-eastern limit of the great valley in which the capital is built. As it lies in the province of Puebla, and is the great feature in the view from that city, it is also called the Puebla Volcano. With the single exception of Mount Elias in Alaska, Popocatepetl appears to be the highest peak in North America, rising as it does in a regular snow-covered cone to an altitude of 17,853 feet. The main mass of the mountain consists of andesite, but porphyry, obsidian, trachyte, basalt, and other similar rocks are also repre sented. Between the pine forest (Pinus accident a I is), which ceases at a height of 12,544 feet, and the snow limit, 14,960 feet, there lies a tract of loose sand, largely composed of grains of sulphur, which renders the ascent tedious and at times dangerous, though the first 1GOO feet can be accomplished on horseback. On the summit is an enormous crater measuring 5000 feet across and with a sheer depth of 2000 feet. The vapours rising from the solfataras, the mixture of sulphur yellow and ash grey in the caldron, the dazzling snow on the edges of the crater walls, and the deep blue of the sky above produce the most indescribable effects of colour. The highest point of the mountain is a softly rounded eminence about 30 feet only from the rim. Sulphur from the crater is regularly worked by a number of Indians who have their huts at the foot of the cone, at a height of 12,000 feet. The material is shot down a slide for a distance of between 2000 and 3000 feet, and the workmen also avail them selves of this means of descent. At the foot of the east slope of Popocatepetl stretches a vast lava field the Malpays of Atlachayacatl, which gives birth to the Rio Atlaco. According to Humboldt, it rises from 60 to 80 feet above the plain, and extends 18,000 feet from east to
west with a breadth of 6000 feet. The date of its formation