VIII.-European Science. On the Longevity of Plants, and the Means of Ascertaining their Age. A tree may be considered in two points of view, either as an assemblage of as many individuals linked together as there are buds developed on its surface; or as a single being, analogous to what is called an individual when speaking of an animal. According to the first, which is probably the most rational view, it cannot be astonishing that, while new buds are incessantly being added to the old, there should be no necessary term to the existence of the aggregate body. By the second, which is the most common, it must be allowed that, as in the greatest number of trees a fresh layer of wood, and in general new organs, are formed every year, there cannot exist in the vegetable world that hardening or that obstruction of the old and permanent organs which produces death from old age properly so called, and that consequently trees should never die but from accidental causes. By either of these hypotheses it is equally shewn that trees do not die of old age in the real sense of the phrase; that there is no definitive term to their existence; and that consequently some may be found that have attained an extraordinary age. But it is not sufficient to advance such an opinion; we must endeavour to prove its truth. Already two remarkable examples have been quoted; that of the Baobab, which ADANSON by ingenious and plausible calculations, has proved to be 5150 years old, and that of the Taxodium (Cupressus disticha, Lin.) which from analogous reasoning may be considered still older. (See the notice on these trees by Mr. ALPH. DE CANDOLLE in the Bibl. Univ. April, 1831.) Other, though less remarkable cases, seem to confirm the idea that there still exists in the world trees of prodigious antiquity, that have witnessed perhaps even its last physical revolutions. It is easy to imagine that many errors may creep into calculations of this sort; and that they can only be depended on as correct, when multiplied cases of vegetable longevity shall be discovered to confirm the fact. I have long occupied myself with this subject, as the publication of the Principles of Botany, inserted (in the year 1805,) in the first volume of the Flore Française, will prove ; but the life of man is too short for such researches: opportunities are rare; and examples should above all be sought for in those countries which are not subject either to frost or to the destructive hand of man. The methods also of proving the age of old trees is not perhaps sufficiently known to travellers, or to those who interest themselves in these kinds of inquiries, and I am therefore induced to call the attention of the public to the subject by means of this pamphlet. A considerable degree of interest would attach to the longevity of certain trees were it only from curiosity. If we consider all the other documents of antiquity as precious, surely we cannot lightly pass over the knowledge that such a tree is contemporary with the oldest times; in some instances, this knowledge might throw light on the history of monuments, as in like manner the history of monuments may assist our inquiries into that of their neighbouring trees. This question might even become of great utility in the history of the globe. If the certified number of these veterans in the vegetable kingdom were to become very considerable; if in the course of time their age were ascertained with greater certainty ; might we not find in these facts some means of fixing the approximate date of the last revolutions of the earth? If inquiries of this kind were made in volcanic or madreporic islands, might they not give some idea of the date of their origin? But ceasing our conjectures on subjects of such magnitude, if we reflect on the means of attaining the solution of the question, we shall see that they are all founded on an exact appreciation of the laws which govern the growth of trees; and this knowledge may throw light on many parts of vegetable physiology and of the forester's art. I believe therefore that such researches may become useful; but even should they prove but curious, I should still not think them unworthy of being offered to the public; for curiosity is an insatiable appetite that the mind of man takes pleasure in satisfying, in proportion to the quantity of food which has already been provided for it. It is well known that plants destined to attain the character of trees may all be classed under two heads. The first, which are the most numerous, have the trunk composed of a body of wood coated with bark; they grow by the annual addition of a new layer of wood, which is produced outside the old wood, but within the bark ; these layers of the young wood being the most exterior, the name exogenous has been given to such plants when speaking of their growth, and that of dicotyledonous when alluding to their germination. Under the second head are placed, on the contrary, all those plants whose trunks, being sensibly cylindrical and generally unadorned by branches, show only a body of wood without any bark properly so called; of which the exterior fibres are the oldest and most hard, and the interior fibres the softest and youngest. They have obtained from this last circumstance the name of endogenous, by which they are distinguished when alluding to their growth, and which is synonymous to that of monocotyledonous, used when speaking of their germination. We will rapidly examine the means of ascertaining the age of individuals belonging to these two classes, and will afterwards add a few remarks on vegetables more humble in their appearance, but whose duration offers matter for special consideration. Almost all trees that are natives of the temperate zones, and consequently of the most civilized parts of the world, are exogenous: their nature and history have therefore been examined much more closely than any others, and may afford us the most interesting data. It is now ascertained beyond a doubt, that exogenous trees increase annually by a new layer of wood, and consequently the number of concentric zones visible on the transversal or horizontal section of a trunk may give an idea of the number of years that have elapsed since the part of the tree under examination began to vegetate. It follows that a slice cut at the bottom of the branch will give the age of the branch; another made at the bottom of the trunk, or at the neck, will give the age of the tree. If, as has been asserted, irregularities may occasionally occur, and this is a very doubtful point, it may at least be affirmed, that the probability of deviation from the law are so slight, that we may boldly argue on the hypothesis that a given number of layers indicates the same number of years' growth; consequently, whenever a clean section of the trunk can be attained, this very simple criterion is sufficient to discover the age of a tree. But the inspection of these concentric zones ought to be made with greater care than has hitherto been bestowed on it. The zones, by their number, give the age; but by the proportion of their thickness they give the mean rate of increase. It is not sufficient therefore to count them, they must be measured. The following is the very simple means I made use of to attain this end. When I met with a clean cut of an old tree, sufficiently healthy to observe its layers, I placed on the branch a slip of paper, reaching from the centre to the circumference; on this slip I marked with a pen or pencil the meeting of each zone, the size of the pith, and that of the bark; writing on it the name of the tree, the country to which it belonged, and any particulars which deserved notice. My collection of these slips, (which have no small resemblance to the measures preserved in a tailor's shop) gives me an exact estimation of the different growth of different trees, and the means of comparing one with another. I take the precaution of marking in a more decided manner every tenth ray, which gives me the average rate of increase for every ten years growth. My measure, being taken from the centre to the circumference, expresses the radius. I double it, if I require the diameter; I take six times if I wish to have the circumference of the woody substance. It is not so useful, except in some particular instances, to make these observations on young trees; for in working on the older ones, of which every species may be procured, there is the advantage of being able to judge of the trees in every stage of their growth. As it would be inconvenient to publish an exact copy of these slips of paper, which are sometimes several feet long, I shall give an idea of their results, by the following table: [We have converted the French lines into English measures.-ED.] Table of the growth of some exogenous trees, as measured by their increase of diameter in periods of ten years, expressed in inches and tenths, English. It results from these observations, that in the advanced periods of their life, trees continue to form layers which do not yield in thickness to those of a middling age; that every species, after having grown rapidly in its youth, appears at a certain age to attain a stated and regular growth. In fact, a tolerably good reason may be assigned for these differences, by assuming, that during the first period, that is to say, before 60 or 80 years, the roots and the branches of forest trees, not being confined by their neighbours, grow freely; but that, after that age, they grow less rapidly, on account of their encountering the roots and branches of neighbouring trees; finally, that inequalities of growth are owing either to the quality of the zone or stratum of earth from which the main portion of the roots are drawing their nourishment, or to the circumstance of the neighbourhood of the tree being more open and clear at some periods. Such calculations made on a great variety of species, and on individual trees of every species, would give the most interesting results regarding the progress of vegetation : 1st. They would establish for each species an average of its annual increase, so that by knowing the circumference of an exogenous tree, its age might be also pretty accurately ascertained. It must be kept in remembrance that great variations take place during the first period, and that afterwards a more uniform growth is established. 2ndly. The mean growth and mean solidity of any species of wood being given, the thickness of the layers of an individual specimen will enable us to judge, whether it possesses all the natural qualities belonging to its species; thus it may be inferred, that the oak No. 1 of the table, is very inferior to the oaks 2 and 3, because the thickness of the layer is too great for the wood to have acquired its full hardness. 3dly. If the law I have assumed is true, that at a certain age (60 or 80 years for oaks) every tree ceases its more rapid growth, and assumes a more regular progress, then we may deduce precise rules as to the most suitable period for cutting down certain trees. I am inclined to believe, therefore, that tables of horizontal cuts would be of very great use, and I recommend their preparation as well to travellers as to those engaged in extensive timber-works and building concerns. 2. When the transverse section of the stump cannot be obtained, a second method presents itself, by which the growth may be determined; which is, to look for the old individuals of every species of which the date is ascertained, to measure their circumference, to deduce from thence their average growth, and to make use of this to calculate the age of other trees of the same species; bearing in mind, that, except in local circumstances, a measure taken from a young tree always produces too great a result for the growth, and too small a one for the age, of old trees. EVELYN mentions, that a Dane, named Henri Ranjovius, planted in Ditmarches, in the year 1580, a certain number of trees of various kinds; that he placed near each a stone recording its date, that posterity might know their age. It would be very interesting to ascertain, whether these trees are still in existence, and if so, to know their circumference; in fact, it would be interesting to have the circumference of every ancient tree the origin of which is known. I invite all who have such particulars, either to publish them, or to communicate them to me; for such observations can only prove useful by comparing them with other recorded facts. 3. For trees of slow growth (séculaires), it is useful to have their circumferences at different known periods, so that they may be compared one with another, or with other measures of the same tree which may be taken sooner or later; these comparisons would afford means for better calculating the law of growth, and of appreciating the influence of differences in age; thus, for example, the cedar in the garden at Paris, which was measured when 83 years old, was 113 inches in circumference, which would indicate an average of nearly 0.44 in. growth in the year, but it was measured when 40 years old, and had then already 84 in. circumference; from which it seems that it grew 0.66 in. a year during the first 40 years, and only 0.23 during the following 43 years: consequently if the age of a very old cedar were required to be calculated, we should not probably go far wrong in taking this last number as a multiplier; thus the cedars at Liban measured in 1660, by MAUNDRELL and Pocock, which were 12 yards and six English inches in circumference, must have been about 609 years old; and in 1787 when they were again measured by Mr. LABILLARDIERE, about 800 years. But the calculation is doubtful since it only rests upon a single example: it would become more certain in proportion as the number of instances becomes greater. 4. It would moreover be useful to take the circumference of very old trees, whenever met with, even when their date is not known. These measures repeated ; at certain intervals would shew the law of increase in the diameter of old trees, and compared with other measures, would afford approximate means for estimating their age. Thus we find from EVELYN that there existed in 1660, an immense oak at Welbeck-lane, which was 33 feet 1 inch in circumference, (nearly 11 feet diameter); this same oak, though mutilated, still existed in 1775, and had a diameter of 12 feet. it had grown 12.6 in. in 120 years, a little more than a tenth of an inch yearly. From whence it may be concluded, that the law of increase, indicated by the oak in my table which was 333 years old, holds nearly good for a tree of much greater age: therefore, if the oak of Welbeck-lane be calculated by the tabular data of the oak of 333 years, it will be found that, in EVELYN's time, it must have been nearly 1300 years old; and more than 1400 years old, in 1775. 5. Finally, in cases where it is impossible to obtain the transversal cut of an old tree, there may be opportunities of making a slight incision on the side and discovering how much it has grown in a given number of years, and thus providing a minimum of its mean growth. This is the method by which ADANSON discovered the age of the Boababs. He saw how much these trees had grown in three centuries, and knowing at the same time the growth of young trees, he was able, by an average, to estimate the general law. The age of the Taxodium of Chapultepec in Mexico might be examined in the same way. By following out the five methods indicated above, either separately or unitedly, the age of old exogenous trees may be ascertained in a manner which will sufficiently answer the subject of this inquiry. Let us now point out the trees to which our attention ought principally to be directed. The greatest longevity in the vegetable kingdom ought to be found, 1st, in trees which by their hardness, their incapacity of decay, or their size, are the best able to resist destructive agents; 2nd, in countries which are not liable to frost or to other causes which too frequently tend to kill large vegetables. Among European trees, we may mention the following examples: 1st. The young Elm, as is known, grows to a large size; but its growth is tolerably rapid. The particular one which I have marked in the table above grew near the town of Morges: the observation of its layers, and the account of its fall, was kindly communicated to me by Mr. ALEXIS FOREL; its section shewed it to be 335 years old; it was at the period of its fall perfectly healthy, and had grown in a humid and light soil: its stem was 17 feet 7 inches in diameter at the neck, 30 feet circumference below the spring of the branches, at 12 feet from the ground; and one of the fine large branches attained 16 feet in circumference; the tree fell in fine weather, the soil having been probably injured by the waters of Lake Leman. It had grown at an average 0.3 in. a year, but if the period be divided into centuries, it will appear that it grew .33 a year during the first century, .23 during the second, and .25 during the third; these calculations accord with those which are generally afforded by young elms planted in front of the French churches by order of SULLY. It is important to distinguish the progress of increase in elms with large from the rate in those with small leaves; the latter are most long-lived and appear to grow more slowly. 2nd. I saw in 1814, at Gigean, near Montpellier, an Ivy tree the stem of which near the ground was six feet in circumference, and which attracted attention by its extraerdinary size. Another ivy, 45 years old, was only 7 inches in circumference. Were this to be taken as an example, the ivy at Gigean must have been 433 years old in 1814, and must now be about 450 years old, if as I hope, it still exists; it is pro |