Art. II.—The Age and Growth of the Kauri (Agathis australis).

Transactions and Proceedings of the Royal Society of New Zealand, Volume 46, 1913, Page 9

Art. II.—The Age and Growth of the Kauri (Agathis australis). By T. F. Cheeseman, F.L.S., F.Z.S., Curator of the Auckland Museum. [Read before the Auckland Institute, 3rd December, 1913.] There is a well-known tendency in human nature to exaggerate that which is really large, and, consciously or unconsciously, to make it appear even larger and more important than it really is. Even in such a matter as the height of the taller trees, their girth, and still more their estimated age, is this peculiarity evident. Take, for instance, the statements that have been made respecting the Dragon-tree of Orotava, in the Canary Islands. This celebrated tree, which was destroyed by a storm in 1851, had a diameter of over 26 ft., and was estimated by some early travellers to have an age of from eight thousand to ten thousand years. Later on these figures were reduced to five thousand or six thousand, and at the present time good authorities consider this estimate far too high. So also with respect to the well-known baobab (Adansonia digitata), which Humboldt speaks of as “being the oldest organic monument of our planet.” In 1750 the French traveller Adanson calculated the age of a specimen observed at Senegal to be over five thousand years. Nowadays it is universally believed that this record is far too high, and was probably based more on vague conjecture than on actual measurement. Coming down to recent times, the immense size of the “big trees” of California (Sequoia gigantea) led to conjectures as to their age varying from three thousand to six thousand years. But when Professor Whitney, the State Geologist of California, took the first accurate measurements it was proved that a tree 24 ft. in diameter con-

tained no more than 1,255 annual rings. Later on a full-sized tree was felled in Fresno County which had a girth of 62 ft. at 8 ft. from the ground, and was 300 ft. in height. Two sections of its trunk were secured, one of which is set up in the Central Hall of the British Museum. Its annual rings have been carefully counted, and proved to be 1,335. It is not now considered probable that any of the existing or recently existing sequoias had a greater age than fifteen hundred years. Similarly the height of the giant gum-trees of Australia was for many years persistently overestimated. In this respect I may appropriately quote some remarks by Dr. A. J. Ewart, given in his memoir “On the Ascent of Water in Trees” (Philosophical Transactions, vol. 199b). At page 367, speaking of the height of the tallest tree in Australia (called by him Eucalyptus amygdalina, but now more generally referred to Mueller's E. regnans), he states that the height of the trees has been greatly exaggerated. “Mueller in his Eucalyptographia gives the heights as observed by Walter (Cape Otway), Robinson (Mount Baw Baw), Howitt (Gippsland), D. Boyle (in the Dandenong Ranges), which are 415 ft., 471 ft., 410 ft., and 420ft. respectively. None of the erect trees appears to have been properly measured, and Boyle's measurement was stated to have been made on a fallen tree from which the top was wanting. The accuracy of the last-named observer is sufficiently indicated by the fact that the height of a tree was first given by him as 525 ft., subsequently reduced to 466 ft., and proved on accurate measurement by Mr. Fuller in May, 1889, to be 220ft. high, and 48 ft. in girth. Various statements as to the existence of specially tall trees of over 350 ft. in height have all proved on proper measurement to be considerably exaggerated when the supposed giant was found. Many fallen giants with heights given as from 450 ft. to 500 ft. evaporated into thin air on the approach of accurate instruments and unbiased observers. The tallest trees are usually found in thick groves or in valleys. The trees of greatest girth are found in the open, but are of less height. The tallest trees measured by Perrin, Davidson, and Fuller were 271 ft., 294 ft., 296 ft., 297 ft., and 303 ft. respectively. The tallest Australian tree, therefore, hitherto accurately measured barely exceeds 300 ft.; and it is possible that some of the records from other countries, notably America, may suffer a similar diminution when accurately tested.” Seeing that the age and size of large forest-trees have been regularly overestimated in other countries, it could hardly be expected that New Zealand would escape similar exaggeration. The kauri pine, the largest of New Zealand trees, has a smaller average diameter than the “big trees” (Sequoia gigantea) of California. But the estimates which have been published of its age are almost as high, and careful writers, such as Mr. T. Kirk and Mr. W. N. Blair, have not hesitated to assign an age of “considerably over four thousand years” (Kirk) or three thousand six hundred years (Blair) to the largest example known; although neither of these gentlemen appears to have counted the annual rings of growth in even a single complete section. As specimens examined by myself many years ago were in direct conflict with these statements, I have been led to examine the question with some care, and have measured and counted the rings of growth in complete sections in various portions of the country The deductions drawn from these measurements, and the general conclusions arrived at, I propose to present to the Institute in this memoir. Before proceeding to give particulars of my own investigations it will be well to briefly state the opinions arrived at by other observers. The

earliest of these is Mr. T. Laslett, author of the well-known book “Timber and Timber-trees.” Mr. Laslett, in his capacity as timber inspector to the Admiralty, made several visits to New Zealand during the years 1840–43, being attached to certain expeditions sent by the British Government for the purpose of procuring spars fit for the topmasts of line-of-battle ships. During these expeditions he had good opportunities of studying the kauri, and from his wide acquaintance with timber and timber-trees, as well as from his scientific training and experience, was well qualified to speak with authority. At pages 44–45 of his book he gives a tabular statement of the number of concentric circles or woody layers found in various timber-trees “within a radius of 3 in., 6 in., 9 in., 12 in., 15 in., 18 in., 21 in., and 24 in., measured from the pith, or centre,” representing, of course, trees with a total diameter of double the radius. From an examination of four kauri sections he arrives at the conclusion that the average number of woody layers required to make 1 in. of wood for a full diameter of 24 in. would be 6·7 for each inch of the whole diameter, equivalent to 13·4 per inch of the radius alone. It will be seen that this represents a somewhat slower rate of growth than that which I have obtained from the examination of a much greater number of sections; but the difference is not very large. If Mr. Laslett's estimates had received proper consideration from subsequent writers many rash and unsupported statements would never have been made. The next writer of note to deal with the age of the kauri was Dr. Hoch-stetter. In his well-known book, “New Zealand, its Physical Geography, Geology, and Natural History,” he gives by far the best and most reliable popular account of the kauri that has yet been published. At page 147 he says, “The oldest and largest trunks attain a diameter of 15 ft., and a height of 100 ft. to the lowest branches, or from 150 ft. to 180 ft. to the top of the crown. Such trees are probably seven hundred to eight hundred years old. Having examined several trunk sections, I found, as the mean result, from ten to twelve rings to 1 in., although in some cases the rings attain a much greater thickness. In some few cases of rare occurrence I have even observed single rings of a thickness of 1 in. For the sawmill the woodcutters generally pick out trees of 4 ft. diameter, with trunks measuring from 60 ft. to 80 ft. to the crown. Such trees are probably two hundred and fifty to three hundred years old.” Hochstetter's estimate of “ten to twelve annual rings to 1 in.” is intermediate between my own and Laslett's; but, on the other hand, his statement that trees with a diameter of 15 ft. “are probably from seven hundred to eight hundred years old” is somewhat under the mark, as it would imply only 8·0 rings for each inch of radius. We now arrive at the views entertained by the late Mr. T. Kirk, a synopsis of which will be found on pages 144–45 of his “Forest Flora.” He says, “A cross-section of a kauri felled in a free-growing condition usually exhibits from seven to thirteen concentric rings to each inch of radius: if we take ten rings as a fair average for growing timber, it would give three centuries as the age of a tree with a diameter of 5 ft. at the base. This rate of increase is supported by the little we know of the rate of growth of young trees. In the Auckland Domain trees planted twenty-two years ago are now 25 ft. high, with a circumference of 26 in., which shows greater rapidity of growth; but the trees are growing under very favourable conditions. Another tree planted twenty years ago is 20 ft. high, with a diameter [? circumference] of only 20 in.” Now, all this is

very just and reasonable, and is evidently based on personal examination. His proposed average of ten annual rings to the inch is almost precisely the same as that obtained by myself (9·7). And his estimate of 300 years as the probable age of a tree with a diameter of 5 ft. at the base, if worked out on the average which my figures have yielded, would only be reduced to 291 years. But, unfortunately, Kirk proceeds to make assumptions respecting the growth of larger trees, for which no sufficient evidence exists, and which are altogether opposed to the information I have been able to obtain. He goes on to say, “The wood of the kauri remains sound long after it has passed its maximum rate of growth; but the newly formed wood cylinders are very thin, while the immense pressure exerted by the outer cylinders consolidates the inner portion of the trunk so that the number of rings to an inch is greatly increased. I have counted over thirty rings to an inch in some gigantic trunks, so that, assuming each ring to represent only a year's growth, the age of a tree 7 ft. in diameter must be 1,260 years. The gigantic specimen at Mercury Bay, which is 80 ft. to the lowest branch and 24 ft. in diameter, must be considerably over 4,000 years; and the fine specimen at Maunganui Bluff, which is 66 ft. in circumference, would not be less than 3,600 years.” Now, the whole of these estimates rest on two assumptions: (1.) That as the tree approaches maturity the newly formed wood cylinders become very thin. This statement is in direct variance with my own measurements of no small number of trees up to 11 ft. in diameter. (2.) That the pressure exerted by the outer cylinders consolidates the inner portion of the trunk so that the number of rings to an inch of radius is greatly increased. But my measurements do not show that the inner rings are “consolidated” in trees of large size; and, in addition, I believe I am correct in stating that authorities in vegetable physiology do not countenance the idea of marked compression of woody tissue in the interior of a trunk due to the successive formation of exterior annual rings. I have already said that the statement made by Kirk to the effect that a tree 5 ft. in diameter would have an average of ten annual rings for each inch of radius, and be 300 years old, must be accepted as a close approximation to the truth. But I fail to see how he can reconcile with it the statement made in the very next paragraph that a tree only 2 ft. wider, or 7 ft. in diameter, would have an age of 1,260 years, with an average of thirty rings for each inch of radius. This is equivalent to saying that during the formation of the additional foot of radius the rate of growth had been diminished to a third of what it previously was. Kirk's contention also implies that the 300 rings which in the 5 ft. tree occupied the radius of 2 ft. 6 in. had been squeezed in the 7 ft. tree into a space of 10 in.! It is unbelievable that the woody layers of a 5 ft. tree could suffer any such compression. But if not, then the 960 annual rings required to make up the full number of 1,260 must be crowded into the extra foot of radius, at the rate of 80 per inch! Not only is such an exceptionally slow rate of growth unknown in the Coniferae, but even no approximation to it has ever been recorded. It is quite clear that Kirk's two estimates are inconsistent one with the other. If the first is accepted, then the second must be swept away. Since Mr. Kirk wrote the “Forest Flora” in 1889 no one has attempted to treat the question in the only accurate manner—that of counting the annual rings of growth in a sufficiently large number of sections of different

diameters and from different localities. In this manner alone can a reliable average of the rate of growth be obtained. It is true that numerous references to the age of the kauri have been published; but apart from some on the rate of growth of planted trees, these consist either of vague statements to the effect that mature trees are of immense antiquity, or of equally vague assertions that they attain an age of several thousand years, periods ranging from three thousand to five thousand years being freely mentioned. My own doubts as to the accuracy of the common belief date back as far as 1884, when I counted the rings of growth in a tree 4 ft. in diameter cut down near Whangarei. To my surprise, I found that the tree had only 188 rings, or 7·8 per inch of its radius. A few years later I examined another tree at Coromandel, with a diameter of 5 ft. 6 in., which proved to have 280 rings, an average of 8·5 per inch. Other trees were counted from time to time; but during the last two years I have been able to obtain quite a number of accurate measurements, amply sufficient, I think, to form the foundation of some general conclusions. Before proceeding to arrange the measurements in tabular form it is well to give an outline of the plan followed in obtaining them. In the first place, it was soon ascertained that if reasonable accuracy were desired it was necessary to examine the trees as soon as possible after they had been cut down. Even after the lapse of a few months only, the surface of the stump becomes covered with numerous cracks, some in a radial direction, or across the rings of growth, and others tangential, or parallel with them. These tiny cracks greatly increase the difficulty in counting the rings. Again, the surface of the stump dries very rapidly, becoming hard and difficult to plane, necessitating constant sharpening of the tool, while the cracks interfere with the production of a smooth surface. In the majority of cases, therefore, a recently cut stump was selected. A track about 4 in. wide was then carefully planed from the circumference to the pith. The majority of the rings could then be counted without any further preparation; but in order to render the whole of them evident the surface was either watered or treated with oil or stain, the plan followed depending on the circumstances of the case. On the whole, I have found that linseed-oil well rubbed in along the smoothly planed track was a perfectly satisfactory mode of treatment. Taking the pith as the starting-point, the rings were usually counted in tens, each group of ten being marked off separately, and the space occupied by it measured. In a similar manner each hundred rings was separately distinguished. The advantage gained by doing this is that when the count is completed it is easy to prepare a chart giving the position of every group of ten or any multiple of ten along the measured radius of the tree, and thus to indicate at a glance any irregularity in the disposition of the rings. And it may be mentioned that such irregularities frequently occur. Before actually commencing to count the rings the greatest and smallest diameters of the trunk were measured, and the position of the pith noted. It is very seldom that the pith is central. In most cases it is decidedly eccentric, and sometimes largely so. In one instance a tree 5 ft. in diameter had its pith only 1 ft. 3 in. from the southern side of the tree. Usually (but not invariably) the centre is nearest to the southern side of the tree, implying that the cambium layer has been most active on the northern side, or towards the sun. Care was also taken to notice the position of the tree as regards its environment—whether sheltered from the wind or sun or exposed to one or both of them; whether the tree was crowded among

other trees of nearly the same age (in which case the rate of growth in diameter was usually slower, although the height of the tree was probably greater). In short, any facts that appeared to be serviceable in the consideration of the question were noted and tabulated. The total number of trees included in the following table is twenty-nine. Of these Nos. 1 to 7 are cultivated trees, the date of planting of which is accurately known. The number of annual rings given for these specimens is the number of years since they were planted, plus three, the estimated age when planted. The rings have been actually counted in a sector of the stem in the remaïning twenty-two; and with the exception of No. 9, which is taken from Mr. Laslett's book, “Timber and Timber-trees” (p. 45), and the last four (Nos. 26 to 29), for which I am indebted to the kindness of Mr. W. A. Nisbet, the countings have been taken by myself. I have, however, to thank my friends Mr. J. Stewart, Mr. T. Herbert, and Mr. C. Spencer for kind assistance with several sections. Table showing the Annual Rings of Growth and their Average to the Radius of certain Sections of Kauri-trees of given Diameter. No. Diameter of Tree. Number of Annual Rings. Average Number of Rings for Each Inch of Radius. Locahty. Authority Ft m. 1 0 8·6 25 5·8 Auckland Domain J. Baber. 2 0 10·6 43 8·1 Parawai, Thames J. W. Hall. 3 0 7·6 43 11·3 " " " 4 0 9·0 43 9·5 " " " 5 0 8·6 38 8·9 " " " 6 0 5·6 38 13·5 " " " 7 0 10·3 26 5·1 Remuera Hon.E.Mitchelson. 8 1 0 42 7·0 Auckland Domain J. Stewart. 9 2 0 161 13·4 (?) T. Laslett. 10 11 0 476 7·2 Waitakerei T. Herbert and T.F.C. 11 4 4 213 8·2 " " 12 5 0 280 9·3 " " 13 5 7 270 8·1 " " 14 8 0 455 9·4 Mangawai J. Stewart and T.F.C. 15 4 0 188 7·8 Whangarei T.F.C. 16 5 6 280 8·5 Coromandel " 17 7 7 448 9·8 Waitakerei C. Spencer and T.F.C. 18 5 11 320 9·0 " " 19 4 2 195 7·8 " " 20 3 8 153 7·0 " " 21 3 3 158 8·1 " T.F.C. 22 3 10 197 8·5 " " 23 7 5 352 7·9 " " 24 4 1 220 9·0 " " 25 3 1 241 13·0 " " 26 3 1 353 19·0 Near Paeroa W.A.Nisbet. 27 6 3 545 14·5 " " 28 7 8 627 13·6 " " 29 8 4 705 14·0 " " Total 282·3 Average 9·7

It thus appears that the examination of twenty-nine sections gives 9·7 as the mean number of annual rings for each inch of radius. An average based upon such a large number of examples cannot be very far from the truth, and we may therefore proceed with some degree of confidence to compare it with the estimates given by Kirk in the “Forest Flora.” Let us take first of all the gigantic tree at Mercury Bay, originally reported and measured by Laslett (see “Timber and Timber - trees,” page 389), and subsequently mentioned by Kirk and others. I have already quoted Kirk's opinion that its age “must be considerably over four thousand years.” The exact figures worked out on his own basis of thirty annual rings per inch would be 4,320. But according to my average of 9·7 rings per inch its age would not exceed 1,396 years. And I prefer to take an estimate which, at any rate, is based upon the measurement of a considerable number of examples, in place of accepting one which is little more than a bare assumption. I consider that Kirk's figures are at least three times the proper amount. Similarly, the specimen at Maunganui Bluff, which is 22 ft. in diameter, and which according to Kirk has an age of 3,960 years, under my views would not exceed 1,280 years. Kirk's assertion that “the age of a tree 7 ft. in diameter must be 1,260 years” I have already combated on the ground that such an estimate is altogether inconsistent with his very reasonable and correct view that a 5 ft. tree would be 300 years old. Worked out on my average of 9·7, the age of the 7 ft. tree would be 407 years, and that of the 5 ft. tree 291 years. The great majority of the kauri-trees that are now cut for sawing range from 3 ft. to 8 ft., and the age of such trees, according to my calculations, and subject only to a very narrow limit of error, would be 174 years for the 3 ft. tree and 465 years for the 8 ft. one. It may be objected that some weight ought to be attached to Kirk's view that in trees of large size the increment of woody tissue formed each year would progressively decline. But as long as the environment of the tree is suitable, and the production of foliage is maintained, there is no reason why that should take place. It is well known that a tree does not cease growing when it arrives at maturity. Professor Marshall Ward says that “as long as it is alive it continues to increase in bulk by the addition of the annual layers developed by the cambium; but when maturity is once passed each succeeding year produces a certain amount of deterioration at the centre.” This deterioration ultimately leads to the tree becoming hollow, but that does not prevent the cambium from forming additional layers. Strasburger says (“Text-book of Botany,” p. 239), “All that is actually visible of a thousand-year-old oak is at most but a few years old. The older parts are dead, and are either concealed within the tree, as the pith and wood, or have been discarded like the primary cortex. The cells of the original growing-point have alone remained the whole time alive. They continue their growth and cell-division as long as the tree exists.” It is almost needless to say that in most parts of the world numerous examples have been cited of hollow trees which are known to have continued their growth for long periods. With respect to the kauri, in trees of large size it is quite common to find the lower part of the trunk hollow. While engaged in measuring the sections just tabulated I noticed several instances the exact age of which I was unable to determine on account of decaying wood or cavities in the centre. All these trunks had well-developed rings of growth near the circumference. One in particular, which measured

8 ft. 3 in. in diameter, and which had a cavity in the centre quite 18 in. across, had its external rings of growth perfectly well developed, the last twenty-five occupying a space of very nearly 2½ in., a rate of growth equivalent to 10·0 rings per inch of radius. This proportion is only very slightly under my general average of 9·7, and is well within the range of variation likely to occur. A further word or two may be expected in reference to Kirk's idea that “the immense pressure exerted by the outer cylinders consolidates the inner part of the trunk so that the number of rings to the inch is greatly increased.” But in making this statement he overlooked the immense strength and rigidity possessed by a column of woody tissue like that of a young kauri, say, 250 years of age. The already completed rings of growth, and especially those constituting the heart-wood, or duramen, have had the walls of their tissues thickened and hardened to such an extent as to constitute a framework, or skeleton, capable of withstanding any pressure that can be exercised by a newly formed woody layer. No doubt each new layer during its formation is subjected to varying strains and stresses, which modify its structure, and which, among other things, produce the well-known differences between the spring and autumn wood; but room for its actual formation is provided by the expansion of the inner cortical tissues, and the consequent fissuring or throwing-off (as in the case of the kauri) of the dead outer cortex. I conclude that Kirk was mistaken in supposing that previously formed annual rings could be materially reduced in thickness by the formation of rings of later growth, and submit the following experimental proof. The tabular statement already given shows the annual rings of growth in twenty-nine sections varying from 6 in. to 11 ft. in diameter. I propose to divide these sections into four groups, as follows: First, those with a diameter under 2 ft.; second, those from 2 ft. to 4 ft.; third, from 4 ft. to 6 ft.; fourth, from 6 ft. to 11 ft. The result is seen in the subjoined table. Group 1. Under 2 ft Diameter. Group 2. 2 ft. to 4 ft Diameter. Group 3. 4 ft to 6 ft Diameter. Group 4. 6 ft. to 11 ft. Diameter. Total Annual Rings for each Inch of Radius for Eight Sections. Average for the Whole Group. Total Annual Rings for each Inch of Radius for Seven Sections. Average for the Whole Group. Total Annual Rings for each Inch of Radius for Seven Sections. Average for the Whole Group. Total Annual Rings for each Inch oif Radius for Seven Sections Average for the Whole Group. 69·2 8·6 76·8 10·9 59·9 8·5 76·4 10·9 General average for the whole of the groups: 9·7. The above table shows no evidence of the number of rings to an inch being “greatly increased” in mature trees The averages for the various groups vary by only 2·4; and the average for trees between 6 ft. and 11 ft. in diameter, which would surely be called mature, is precisely the same (10·9) as that for trees between 2 ft. and 4 ft., and is very far removed from Kirk's suggested rate of thirty per inch for a 7 ft. tree. Irregularities in the rate of growth of individual trees, however, are not uncommon, and may occur at any period of the life of the tree. It may be interesting to give a table of the rate of growth of an 11 ft. tree, the largest I have measured, and which, curiously enough, was also the most irregular in growth. For comparison I have included a similar table of

a tree, 5 ft. 11 in. in diameter, in which the disposition of the rings was remarkably regular. Rate of Growth of Kauri-tree 11 ft. in Diameter, measured on the narrowest radius (52·22 in.) from the pith to the circumference. (On account of the scarf made in cutting down the tree it would have been difficult to measure the tree on the longest radius.) Rate of Growth of Kauri-tree 5 ft. 11 in in Diameter, measured on the radius of 35·92 in? Rings of Growth (equal to Years of Ago), arranged in Groups of 25 Space in Inches occupied by each group of Rings. Rings of Growth (equal to Years of Ago), arranged in Groups of 25 Space in Inches occupied by each group of Rings. 25 1·00 25 2·50 50 1·12 50 3·00 75 3·00 75 3·25 100 3·50 100 3·25 125 3·00 125 3·12 150 2·00 150 3·62 175 3·50 175 3·12 200 2·75 200 2·62 225 3·75 225 3·00 250 6·62 250 2·62 275 4·62 275 2·25 300 3·75 300 2·12 325 2·50 320 1·45 350 3·25 375 2·75 400 2·62 425 3·12 450 0·75 476 1·18 Age of tree, 476 years. Average number of rings per inch of radius (5 ft. 6 in.), 7·2. Age of tree, 320 years. Average number of rings per inch of radius (2 ft. 11 in.), 9·1. Comparing these two tables, the first point to notice is the great difference in the rate of growth of the two trees during the first fifty years. The 11 ft. tree produced only 2·12 in. of radius during this period, showing an average of 23·6 rings per inch of radius; while the smaller tree built up 5·5 in. of radius, with an average of 9·09 per inch, its rate of growth being approximately two and a half times as great. But the rate of growth of a young kauri probably depends very largely on how far it is crowded by other trees. In support of this view, Mr. J. W. Hall, of Thames, has drawn my attention to the different behaviour of two trees of equal age in his plantation at Parawai (Nos. 5 and 6 of my tabular list). No. 5, planted in an open situation, has formed 4·3 in. of radius in thirty-eight years; No. 6, much crowded by other trees, had only produced 2·8 in. in the same period. The number of rings per inch of radius in these two trees works out at 8·9 and 13·5 respectively. The most interesting peculiarity disclosed by the ring measurement of the 11 ft. tree is the enormous increase of growth which took place between the 225th and 250th years, when no less than 6·62 in. of radius, equivalent to 13·24 in. of diameter, was formed, being at the rate of 3·7 rings for each inch. This is the largest rate of growth for a series of rings that I have observed, although single rings are sometimes seen from half an inch

to nearly an inch in diameter. The rate of growth continued very high for the next group of twenty-five rings, 4·62 in. of radius being built up, and was considerably above the average in the following one. During the seventy-five years covered by these three groups the tree increased its diameter by 2 ft. 6 in. After the 425th year of the age of the tree, or fifty-one years before the present time (1913), a remarkably sudden slackening in the rate of growth took place, only ¾ in. of woody tissue being formed during the next twenty-five years, although 3·12 in. had been produced during the previous twenty-five. The rate did not nearly recover itself before the tree was cut down, the increase of woody tissue during the last twenty-six years occupying only 1·18 in. I was able to prove, however, that the slackening in growth was mainly a local peculiarity, confined to one portion of the circumference of the stem, for by planing to the right and left of the track along which the measurements had been made the crowded rings were seen to gradually open out until they occupied a greater diameter. My main object in drawing attention to the peculiarities of the 11 ft. tree is to show how dangerous it is to estimate the age of any tree from counting the annual rings of part of a section only. If, for instance, the rings in the present example were known for only the 5 in. nearest the centre, or the 5 in. nearest the circumference, then for those portions the rate of fifteen rings per inch could be established, and, calculating on that basis alone, the age of the tree would be 990 years. On the other hand, if a portion in the centre had been selected—say, from the 225th to the 300th rings—then the average number of rings per inch would not exceed five, and the age of the tree would work out at 330 years only. On an actual count of the whole of the rings, the age of the tree was ascertained to be 476 years, the percentage of the annual rings to each inch of the radius being 7·2. One point of some importance still remains to be mentioned. At page 144 of the “Forest Flora” Mr. Kirk says, “It is uncertain whether the kauri forms only a single cylinder of wood during each year or more: the balance of evidence is in favour of the latter view.” Kirk nowhere states the nature of this evidence; nor does he act upon the belief in his calculations as to the probable age of the tree, all of which are based on the assumption that only one cylinder is produced in each year. Obviously, the rings of growth would be of little value for determining the age of the tree if there was any uncertainty as to their being of yearly production. Fortunately, however, this uncertainty has been removed by direct evidence. In the year 1865 several young kauri-trees and certain New Zealand taxads were planted in the Auckland Domain. In 1905 it became necessary to remove some of them, and at my suggestion Mr. James Stewart obtained cross-sections of the trunks. In all cases the number of concentric rings of growth agreed with the number of years since the trees were planted. Mr. Stewart's results, which are embodied in a paper printed in our Transactions (vol. 38, p. 374) may be taken as proving that the New Zealand gymnosperms do not produce more than a single well-defined cylinder of woody tissue in each year. The conclusions that can be drawn from this investigation may be summarized as follows:— 1. That the statements made regarding the age and rate of growth of the kauri have for the most part been greatly overestimated, and particularly so for trees exceeding 5 ft. or 6 ft. in diameter.

2. That the number of measurements of trees of all sizes under 12 ft. diameter is now sufficiently large to admit of the determination of an average rate of growth, and that this rate can be stated with some confidence at 9·7 years for every inch of the radius of the tree. 3. That although the greater number of examples will be found in the neighbourhood of the general average, marked deviations may be occasionally seen; although, as these occur both above and below the average, they do not materially influence the position. 4. That as regards trees of greater diameter than 12 ft. some slight uncertainty may still exist as to their age, on account of the total absence of measured sections. But as no progressive decline in the diameter of the annual rings has been found in the largest trees yet examined, and as a tree of very large diameter is almost certainly a tree that has grown unusually fast at one period of its life (see previous references to the 11 ft. tree), there seems to be no reason for assuming that the average rate of growth is materially different. 5. That although the kauri is not so excessively slow in its growth as has been supposed, it is much slower than most trees of economic value. A tree 2 ft. in diameter would have an average age of 116 years; one of 3 ft., 174 years; and one of 4 ft. would be 232 years old. Periods like these are much too long to offer any hope of monetary return from the planting of kauri, even if there were not other reasons to advance against such an undertaking.