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THE POTTERY TREE OF PARA.
BY JOHN R. JACKSON.
(With a Plate.) AMONGST vegetable economic products the barks of various plants hold a prominent place, whether for medicinal, manufacturing, or other purposes. The structure and formation of all barks are more or less similar, though the contents of the cells vary much in different plants, thus we have soft or fibrous, hard or woody, and even stony barks, and the bark of the pottery tree of Para is a notable example of this latter. To outward appearance the formation of the bark in many plants would appear to bear no relation one with another, as, for instance, the cork of commerce compared with its near ally, the bark of the common oak, and again with the fibrous barks of many of our British trees. Naturally, the bark of a tree is, at first, composed of uniform cellular tissue, similar to the tissue of the central portion of the stem. The formation of the layers in the fully-developed bark is on the reverse system to that of the woody layers of the stem, the inner portion being the most vascular, and the outer portion the most cellular. Between the wood and the first formation of bark lies the cambium layer, a single series of nucleated cells, which originally are connected with both wood and bark, and perform certain functions in the formation of the woody fibres of the inner bark, and likewise in adding to the cells of the medullary rays of the wood. The innermost part of the bark next the wood, or rather next the cambium layer, is called the liber, or endophlæum ; next to the liber, which is the fibrous part, the cellular part is placed, called the mesophlæum, or middle bark, and next that the epiphlæum, or outer bark. These three divisions are usually included under the general term of cortical layers. It is from the liber, or inner bark, which is composed of fibres more or less long and tenacious, that our most valuable commercial fibres are obtained.
In some plants the fibrous system prevails through the inner bark, but we shall have occasion to speak more fully upon these particular kinds at another time. What we have to deal with at present is a noted example of the harder, more woody, or more silicious barks, which example is to be found in the Para pottery tree. This is a large tree of very straight and slender growth, attaining a height of 100 feet before giving off any branches; the diameter of the base is seldom more than one foot, and rarely exceeds fifteen inches. The wood itself is very hard, and, as will be presently seen,
VOL. XII.—NO. I.
barked the liber, or rellular part is the epiph
contains a great deal of flinty matter. The tree-which is called in Spanish El Caouto, or El Caouta; in French, Bois de Fer; in Brazil, Caraipe; and in English, pottery tree—is now known to botanists as the Moquilea utilis, H.f. Aublet was the first to bring the tree into notice, and it was at one time placed in the natural order Ternstræmiacee, under the name of Caraipa angustifolia. Further information and research, however, has caused it to be placed where it now is. Sound and durable as the wood is, it is on the bark that the natives set the greatest value. The Indians employed in the manufacture of pottery from its bark always keep a stock of it in their huts for the purpose of drying or seasoning it, as it burns more freely, and the ashes are collected with greater ease than when it is fresh. For the manufacture of the pottery the ashes of the bark are powdered and mixed with clay, the purest clay that can be obtained from the beds of the rivers is preferred on account of its taking up a larger quantity of the bark ash, and producing a stronger kind of ware. The most valued bark, or that which contains the largest quantity of silex, is produced by trees which grow in a rich but dry soil. Those growing in low or sandy forests being much inferior in the quality of this deposit. In the best kinds the silex can readily be seen with the naked eye, but to test the quality of the various kinds of bark, the natives burn it and then try its strength between the fingers; if it breaks easily it is considered of little value, but if, on the contrary, it requires a pestle and mortar to break it, its quality is pronounced good. Though the proportions of ash and clay are varied at the will of the maker, and according to the quality of the bark, a superior kind of pottery is produced by mixing equal portions of fine clay and powdered ashes of the bark. all sorts of vessels of large or small size, for domestic or household use, are made of this kind of ware, as well as vases or ornamental articles, some of which are painted and glazed as in Fig. 6, which is a representation of a specimen in the Kew Museum. The figures upon this vase are not burnt in, but are merely superficial, the colour being laid on with a brush and secured by a coat of glaze. Fig. 5 is a representation of an unglazed pot, with lid, the figures of which are in relief. Articles made of this ware are very durable, and will bear almost any amount of heat; they are consequently much used by the natives for boiling eggs, heating milk, and, in short, for general culinary purposes.
Having shown the great value of this bark to the natives for a purpose which, to say the least, is novel in the application of barks, we will endeavour to arrive at the cause of such an adaptation by a brief exposition of its component parts.
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The bark seldom grows more than half an inch thick, and is covered with a skin or epidermis frequently covered with lichens. A superficial examination shows nothing out of the common; the fresh bark, however, cuts somewhat similar to a soft sandstone, but, when dry, it is very brittle and flint-like, and sometimes difficult to break. By biting a piece of the bark the presence of silex can be well ascertained, as it grates between the teeth like fine sand. If we examine a section under the microscope, we find all the cells of the different tissues or layers are more or less silicated, the silex forming in the cells while the bark is very young. In the inner bark the silex or flint is deposited in a very regular manner, as will be seen by Fig. 1. The flint, however, from the ash of a porons cell of the bark assumes a very different appearance, as shown in Fig. 2. Fig. 3 shows a porous cell macerated, and Fig. 4 is a flint skeleton from a similar cell. The bark of young trees and branches contain a much larger quantity of water than that of old trees; the proportion of water, however, are more equal in the old and young woods. From an analysis made of both the old and young barks, the old was found to give 30.8 per cent. of ash, and the young bark 23.30. Of the different layers of the old bark, the outer gave 17.15 per cent., the middle 37.65, and the inner 31. A larger percentage of ash was yielded by the bark of an old branch, which was found to give 77. In comparison to the bark the wood is relatively poor in silex, the duramen, or old wood of an old trunk, giving only 2.5 per cent., and the alburnum, or young wood, 2 per cent. only.
The wood, bark, ash, and various specimens of the manufactured pottery, may be seen in the Kew Museum.