AGE OF TREES. The immense con sumption of timber in the manufactures of this and many other countries, renders it in teresting to note the circumstances which distinguish different kinds of trees, in respect to duration and growth.
Besides annual and biennial plants (whose age is indicated by their names), the remain der of the more perfect part of the vegetable kingdom, whether herbaceous or shrubby or erborescent, consist of plants which may be classed under two principal modes of growth. One of these modes is to increase, when young, in diameter, rather than in length, until a certain magnitude is obtained, and then to shoot up a stem, the diameter of which is never materially altered. The addi tion of new matter to a trunk of this kind takes place by the insinuation of longitudinal fibres into the inside of the wood near the centre ; on which account such trees are called Endogenous: they also bear the name of Monocotyledons. The other mode is, from the beginning, to increase simultaneously in length and diameter, hut principally in length. The addition of new matter to a trunk of this kind, takes place by the insinuation of longi tudinal fibres into a space beneath the bark, and on the outside of the wood near the cir cumference ; on which account such trees are called Exogenous ; they also bear the name of Dicotyledons.
To the first of these classes belong the palm tribe and some other tropical trees. There is scarcely any well-attested evidence of these plants ever acquiring any considerable, age. It has indeed been supposed, that cer tain Brazilian cocoa-nut palms may he from 600 to 700 years old, and that others probably attain to the age of something more than 300 years. But the method of computing the age of palms, which is either by the num ber of rings externally visible upon their rind between the base and the summit of the stein, or by comparing the oldest specimens, the age of which is unknown, with young trees of a known age, is entirely conjectural, and not founded upon sound physiological considera tions ; besides which, the date-palm, which is best known to Europeans, does not at all justify the opinion that palms attain a great age ; the Arabs do not assign it a greater lon gevity than from two to three centuries.
But in exogenous trees, it is quite the re verse : to their existence no limited duration can be assigned. Of the many remarkable cases upon record of a great age attained by exogenous trees, the following are among the more interesting.
At Ellerslie, the birth-place of Wallace, three miles to the S. W. of Paisley, stands an oak, in the branches of which tradition relates that celebrated chieftain to have concealed himself with three hundred of his followers. However
improbable the latter circumstance may be, it is at least certain that the tree may well have been a remarkable object, even at the period assigned to it by tradition, namely, in the be ginning of the fourteenth century, and if so, this individual must be at least 700 years old. Its branches are said to have once covered a Scotch acre of ground ; but its historical in terest has rendered it a prey to the curiosity of the stranger, and the limbs have gradually disappeared till little remains except the trunk. Many other cases of oaks of extreme old age are recorded, some of which have been estimated at 1500 or 1000 years.
Of ancient yews several authentic instances can be named. At Ankerwyke House, near Staines, is a yew older than the meeting of the English barons at Runnymede, when they compelled King John to grant the Magna Charta. This tree, at 3 feet from the ground, measures 0 feet 3 inches in diameter ; and its branches overshadow a circle of 207 feet in circumference. The yews of Fountain's Ab bey, in Yorkshire, are probably more than 1200 years old ; and to others an ago of from 2500 to 3000 years has been assigned.
Even this degree of antiquity is, much less than that of the baobab trees of Africa, estimated by Adanson at 5000 years: and the deciduous cypress of Chapultepec in Mexico, which the younger De Candolle con. siders still older.
The way in which the age of some of these specimens has been computed is twofold firstly, by comparing them with other old specimens, the rate of growth of which iE known; and secondly, by cutting out a portion of their circumference, and counting the num. ber of concentric rings that are visible ; for in exogenous trees the woody cylinder of one year is divided from the succeeding one by t denser substance, which marks distinctly the line of separation of the two years. The first of these methods is sufficiently correct to give at least an approximation to the truth, and die latter would be absolutely correct, if one could be quite sure that observers provided against all possible causes of error. But it has been shown by Dr. Lindley, that in con sequence of the extreme inequality in thick ness of the annual layers of wood on opposite sides of a stem, a person who judged of the whole age of a tree by the examination of the layers of the stunted side only, would commit errors to the amount of sixty per cent. and more. It is by no means impossible that the great age assigned to the deciduous cypress and the baobab may be connected with an error of this nature.