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in several species, and especially those of the prunus and salix, cherry and willow tribes, if the stem branches be bent down to the earth, plunged into it, and continued in this situation for a few months, these branches will throw forth radicles; and if, after this, the original root be dug up, and suffered to ascend into the air, so that the whole plant become completely inverted, the original root will throw forth stem-branches and bear the wild fruit peculiar to its tribe. The rhizophora Mangle, or mangrove-tree, grows naturally in this manner; for its stembranches, having reached a certain perpendicular height, bend downwards of their own accord, and throw forth root branches into the soil, from which new trunks arise, so that it is not uncommon, in some parts of Asia and Africa, to meet with a single tree of this species covering the oozy waters in which it grows with a forest of half a mile in length. The ficus Indica, or banyan, grows in the same manner, and often with enormous trunks, equally derived from a primary root. The largest tree of this kind known to Europeans, is on an island in the river Nerbedda in the Guzzerat, distinguished in honour of a Bramin, of high reputation, by the name of Cubbeer Bur. High floods have destroyed many of its incurved stems, yet its principal stems measure two thousand feet in circumference, the number of its larger trunks, each exceeding the bulk of our noblest oaks, amount to three hundred and fifty, while that of its smaller are more than three thousand; so that seven thousand persons may find ample room to repose under its enormous shade, and may at the same time be richly supplied from the vast abundance of fruit which it yields in its season.
The solid parts of the trunk of the plant consist of CORTEX, cuticle, or outer bark; LIBER, CUTIS, or inner bark; ALBURNUM, or soft wood; LIGNUM, or hard wood*; and MEDULLA, or pith. Linnæus gave the name of medulla to the pith of plants upon a supposition that it had a near resemblance to the medulla spinalis of quadrupeds. A closer investigation, however, has since proved that this resemblance is very faint, and that the pith or medulla of vegetables consists of nothing more than a mere spongy cellular substance, forming, indeed, an admirable reservoir for moisture; and hence of the utmost importance to young plants, which, in consequence of their want of leaves and branches, whose surfaces are covered with the bibulous mouths of innumerable lymphatics, would otherwise be frequently in danger of perishing through absolute drought; but gradually of less use
* There is a curious paper of Count Rumford's, mentioned among the labours of the French Imperial Institute for 1812, upon the chemical properties of the different parts entering into the composition of the trunk of trees; for an account of which see also Thomson's Annals of Philos. vol. i. p. 386. By a variety of experiments Count Rumford was led to this singular conclusion, that the specific gravity of the solid matter which constitutes the timber of wood is almost the same in all trees. By the same means he determined that the woody part of oak in full vegetation is only four-tenths of the whole. Air constitutes one-fourth of it, and the rest consists in sap. Light woods have still a much less quantity of solid matter: but the season of the year and the age of the tree occasion considerable variations. Ordinary dry wood contains about one-fourth of its weight of water. Even the oldest wood, though in the state of timber for ages, never contains less than one-sixth of its weight of water. All absolutely dry woods give from 42 to 43 per cent. of charcoal: whence he concludes, that the ligneous matter is identic in all woods.
as the plant advances in age, and becomes possessed of these ornamental appendages; and hence, except in a few instances, annually encroached upon, and at length totally obliterated by the surrounding lignum.
All these lie in concentric circles; and the trunk enlarges, by the formation of a new liber, or inner bark, every year; the whole of the liber of one year, excepting indeed its outermost layer, which is transformed into cortex, becoming the alburnum of the next, and the alburnum becoming the lignum. Such, at least, is the common theory, and which seems to be well supported by the experiments of Malpighi and Grew; but it has lately been controverted by Mr. Knight, who contends, that the liber has no concern in the formation of new wood, which proceeds from the alburnum alone, a new layer of alburnum being formed for this purpose annually. I cannot discuss the argument at present: nor is it of any great importance; since, under either system, it is obvious that a mark of any kind, which has penetrated through the outer into the inner bark, must in a long process of years be comparatively transferred to the central parts of the trunk. On which account we often find, in felling trees of great longevity, as an oak, for example, the date of very remote national æras, and the initials of monarchs, who flourished in very early periods of our national history, stamped in the very heart of the timber on its being subdivided.
Some of these memorials are very curious, and M. Klein, the well-known Secretary of Dantzic, has given various examples in his letter to Sir Hans
Sloane, Bart., the President of the Royal Society.* One of these consists of a long series of letters discovered, in 1727, in the trunk of a full grown beech, near Dantzic, in land belonging to the family of Daniel Berckholtz. The letters D. B. were chiefly conspicuous in the solid wood; the wood towards the bark, and that towards the heart, that is, in each extremity, "bearing not the least trace of letters." It was ascertained that the letters had been cut in the year 1672, more than half a century previously to their discovery within the solid wood. M. Klein relates another example from the Ephemerides of Natural Curiosities +, recorded by Joannes Myerus. It consists of a thief hanging from a gibbet, apparently drawn by nature's own pencil in the timber of a beech-tree as also the figure of a crucified man, found in a tree of the same kind; and that of a chalice with a sword, perpendicularly erect, sustaining a crown on its point; which was preserved at the Hague, and had been seen by himself.
Such marks were formerly attributed to miraculous intervention, or regarded as marvellous sports of nature; but the hints now offered will easily explain their origin.
Foreign substances have often been found imbedded in the same way, having at one time been sunk into the inner bark, or penetrated it by a wound or other excavation, and afterwards covered over with new annual growths of liber and alburnum. Thus Sir John Clerk gives an account of a horn of a large deer which was found in the heart of an oak
*Phil. Trans. for 1739, vol. xli. p. 231.
vol. viii. p. 360.
+ Ephem. Nat. Cur. decad. iii. an. v. obs. 29.
in Winfield Park, Cumberland, fixed in the timber with large iron cramps, with which, of course, it had been fastened on.* And we are hence able to account for the occasional detection of a capricorn beetle, or other insect which has been found in the centre of a trunk, the animal having crept into an accidental cleft, and either died there naturally, or been arrested and imprisoned by the secretion of the matter of new inner bark while in the torpitude of its aurelian state. And hence, indeed, the cause of the very wonderful phænomena of toads or frogs being at times found in a like situation; having in the same way been impacted in the hole or crack into which they had crept, by the glutinous fluid of the inner bark, during sickness or a protracted winter sleep. Some of these are found alive when the tree is cut down, deriving both air and nutriment enough from the surrounding vessels of the tree during their imprisonment. In the Memoirs of the Paris Academy there is an example of a toad found in a tree that was proved to be a century old.‡
As the series of concentric circles, produced in the trunk of a tree by the growth of every year, are still visible after the conversion of every other part into lignum or hard wood, we can trace its age with a considerable degree of certainty, by allowing a year for every outer circle, and about two or three years for the complete lignification of the innermost. §
*Phil. Trans. for 1740, vol. xli. p. 448.
+ Id. 1741, vol. xli. p. 861.
Mém. de l'Acad. Par. 1731. p. 24.
§ The palms form an exception to this general rule, possessing neither proper bark, nor fascicles of vessels displayed in