UNIVERSITY OF CALIFORNIA 
 AT LOS ANGELES 
 
 GIFT OF 
 
 CARNEGIE INSTITUTION 
 OF WASHINGTON
 
 GROWTH IN TREES 
 
 BY 
 
 D. T. MACDOUGAL 
 
 PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON 
 WASHINGTON, 1921 
 
 8T43
 
 GROWTH IN TREES 
 
 BY 
 
 D. T. MAcDOUGAL 
 
 PUBLISHED BY THE CARNEGIE INSTITUTION OF WASHINGTON 
 WASHINGTON, 1921
 
 CARNEGIE INSTITUTION OF WASHINGTON 
 PUBLICATION No. 307 
 
 PRESS OF GIBSON BROS., INC. 
 WASHINGTON, D. C.
 
 
 
 GROWTH IN TREES. 
 
 BY D. T. MACDOUGAL. 
 
 A tree may be considered as a tall cone of wood terminating in leafy 
 expanses. The base of the cone is subdivided into myriads of rootlets, 
 through the surfaces of which the soil-solutions enter, and the water, 
 pas?ing upward, is transpired from the leaves. The trunk of a tree 
 is largely composed of dead cells, but inclosing it is a thin sheet of 
 spindle-form cambium cells 1 in 2 to 10 or more layers, which in the 
 growing season enlarge in thickness and divide lengthwise, those on the 
 outside becoming transformed into cork and phloem and those on the 
 inner into wood cells and vessels. Extending from the center of the 
 trunk are thin sheets or rays of the medulla or pith of the young stem. 
 The most recently formed cells of these elements are still living and in 
 some trees the medullary cells remain alive for several years, so that 
 the woody cylinder of the tree may comprise wood-cells or tracheids, 
 vessels, and thin-wall ray cells, some of which are alive. External to 
 the cambium are sieve cells, bast fibers, etc., and cork cells, inclosed in a 
 bark which varies widely as to structure in different species. 
 
 The greatest amount of increase or change in volume is that which 
 results from the multiplication by fission of the cambium cells, and 
 their enlargement accompanied by the differentiations mentioned, all 
 based upon hydration of cell-colloids. 
 
 When changes in the entire diameter are measured the variations 
 may be due to the action of any one of these tracts of tissue. The 
 colloids of the cell, including those of non-living walls or wood, are 
 practically never in a stable condition, but follow an ever-varying 
 environment in resultant adjustments, especially with respect to the 
 water which they contain. All plants except submerged forms are 
 always losing water at a varying rate from part of their surfaces, while 
 water may be entering absorbing surfaces at a varying rate, and as a 
 consequence of the inequality the volume may increase or decrease 
 according to the balance between gain and loss. 
 
 Growth in organisms is essentially a hydration of colloids of the 
 protoplasm accompanied by metabolic changes which result in the 
 conversion of materials in the cell-sap to the emulsoid condition charac- 
 teristic of living matter. Both processes, one of adsorption and the 
 other a result of shifting equilibria in chemical systems, cause an 
 
 1 Bailey, I. W. Phenomena of cell-division in the cambium of arborescent gymnosperms and 
 their cytological significance. Proc. Nat. Acad. Sci., 5: 283-285. 1919. 
 
 209253
 
 4 GROWTH IN TREES. 
 
 increase of the volume of the protoplasm and an'enlargement of the 
 cell-mass of which it forms a part. 
 
 Any instrumentation of sufficient accuracy and delicacy to measure 
 the increases or variations due to growth in the cambium layer will at 
 the same time include the variations in volume of the woody cylinder, 
 which is also the conduit through which liquid passes from the roots 
 to the crown. Similar conditions prevail in nearly all higher plants, 
 and growth measurements of all stems, leaves, and roots include 
 changes in woody or non-living cells. 
 
 Such trees as the birch, with 200,000 leaves, are reputed to transpire 
 as much as 400 liters in a single day. No estimates of the pines are 
 available, but the low moisture content of the soil around the roots of 
 the Monterey pine would not furnish a supply for such use of water. 
 The trunk of a tree may, in fact, be compared to the supply hose of a 
 fire-engine coupled to a hydrant. When the pressure from the mains 
 is enough to supply water faster than it can be pumped out, the hose is 
 distended. When the engine tends to take water faster than it would 
 be delivered by the system, the hose would tend to collapse. Some- 
 thing of this sort takes place in many trees which have been kept under 
 observation. The conduit in this case, however, is not a simple pipe 
 or a set of pipes, but is made up of vessels, through which water may 
 pass under capillary conditions, and inclosed box-like tracheids which 
 may be only partially filled with water. When water is withdrawn 
 from such a system faster than it is taken in, the resulting changes in 
 form and size are complex hi character. 
 
 These facts were well considered in my experiments previously 
 carried out when the measurement of growth in trees was taken up 
 in 1918, and a new technique with specially designed instruments 
 was found necessary for the analytical study of the changes in volume 
 of these massive organs. The records are now continuous for a large 
 number of trees for many months, one tree having been under con- 
 tinuous measurement since September 1919. The chief features 
 considered in the present paper are as follows: 
 
 1. The dendrograph, an instrument for making continuous records 
 of the variation of tree trunks, has been developed to an approximately 
 final form. 1 The essential feature of this instrument consists of a 
 floating frame of metal of low temperature coefficient, such as invar 
 or bario, which may be placed around a tree trunk, and the variation 
 
 ^acDougal, D. T. The dendrograph: a new instrument for recording growth and other varia- 
 tions in the dimensions of trees. Carnegie Inst. Wash. Year Book for 1918, pp. 59-60. 
 
 . The dendrograph. Carnegie Inst. Wash. Year Book for 1919, pp. 72-78. 
 
 . The course of growth in trees as measured by the dendrograph. Carnegie Inst. 
 
 Wash. Year Book for 1920, pp. 51-52. 
 
 . Measurement of a season's growth of trees by the newly designed dendrometer. 
 
 Carnegie Inst. Wash. Year Book for 1920, p. 52. 
 A brief discussion of the contents of the present paper was given before the American 
 
 Philosophical Society at Philadelphia, April 22, 1921, which is in press in the Proceedings of 
 
 the Society.
 
 GROWTH IN TREES. 5 
 
 in distance between a contact rod on one side of the trunk and of one 
 end of a rod or lever on the other side is traced by a pen on the free 
 end of a lever on a sheet of paper carried by a recording cylinder. 
 Such measurements are in terms of the diameter. 
 
 2. A dendrometer, of simple design and non-expensive construction, 
 has been perfected, which may be placed around the trunk of a tree 
 and the size of the trunk read on a dial from time to time. The 
 essential parts of this instrument are an encircling wire engaged with 
 a number of bearing levers. One end of the wire is anchored and the 
 other is attached to the short end of a lever, the free end of which moves 
 over a scale giving readings of the size of the trunk in terms of several 
 radii, or of the circumference. 
 
 3. Dendrographic records of trees have been made as follows: 
 
 Citrus aurantica: Citrus Experiment Station, Riverside, California; by H. S. Reed. 
 
 Fagus grandifolia: Baltimore, Maryland; by B. E. Livingston. 
 
 Fraxinus arizonica: Tucson, Arizona; by H. W. Fenner. 
 
 Juglans major: Carmel, California; by D. T. MacDougal. 
 
 Parkinsonia microphylla: Tucson, Arizona; by B. R. Bovee. 
 
 Picea pungens: Cottonwood Nursery, Wasatch Mountains, Utah; by C. F. Korstian. 
 
 Pinus chihuahuana: 6,000 feet altitude, Santa Catalina Mountains, Tucson, Arizona; by 
 
 D. T. MacDougal and B. R. Bovee. 
 Pinus ponderosa: Alpine Laboratory, Pikes Peak, Colorado; by F. E. Clements and Gorm 
 
 Loftfield. 
 
 Pinus radiata: Seven trees, Carmel, California; by D. T. MacDougal. 
 Pinus scopulorum Lemmon: Fort Valley Experiment Station, Flagstaff, Arizona; by G. 
 
 A. Pearson. 
 
 Platanus occidentalis: Missouri Botanical Garden; by B. M. Duggar and F. S. Walpert. 
 Populus deltoides: Missouri Botanical Garden, by B. M. Duggar and F. S. Walpert. 
 Populus macdougalii: Continental, Arizona; by W. B. McCallum. 
 Pseudotsuga mucronata Sudworth: Alpine Laboratory, Pikes Peak, Colorado; by F. E. 
 
 Clements and G. Loftfield. 
 Quercus agrifolia: two trees, Carmel, California; by D. T. MacDougal. 
 
 4. The trees noted above represented deciduous and evergreen 
 coniferous types native to the Atlantic seaboard, the Mississippi valley, 
 various elevations hi the Rocky Mountains, the plateau, mountain 
 slopes, and desert valleys of Arizona, the plains of southern California, 
 and the coastal region at Carmel, with a wide variety of climatic con- 
 ditions and seasons. 
 
 5. The period in which enlargement of trunks takes place is com- 
 paratively brief, even in places in which the season is of indeterminate 
 duration. 
 
 6. Growth is an activity of an embryogenic tract of tissue, which 
 depends upon environmental conditions, and no part of the observa- 
 tions suggested a seasonal rhythmic action. The Chihuahua pine, 
 which exhibits growth of the trunk with that of the branches on the 
 dry mountain slopes in the advance of the temperatures in May and 
 June, is brought to rest coincident with the desiccation of the soil in 
 the dry fore-summer. Reawakening ensues consequent upon the sum- 
 mer rains, and enlargement continues until checked by the decreasing 
 temperatures and increased soil desiccation in the autumn. The
 
 6 GROWTH IN TREES. 
 
 Monterey pine (Pinus radiatd) shows beginning growth of the trunks 
 with the advance of temperatures, January to April, and comes to 
 rest in July with the desiccation of the soil. Quercus agrifolia in the 
 same region begins earlier and ceases to grow in June or July. Both 
 may be awakened in July or August by deep irrigation of the soil. 
 
 7. The trunks of all the trees measured show a daily variation in 
 size, by which the maximum is reached shortly after sunrise and the 
 minimum at a time after noon, dependent upon external agencies. 
 These variations appear to depend upon the water-balance in the 
 woody cylinder, are greatest in the seasons in which water-loss from 
 the crown is greatest, are least in the cooler or damper seasons, and 
 are to be detected in the records even in the period of most rapid 
 enlargement of the trunk. 
 
 8. Measurement of variations in the woody cylinder were taken by 
 arranging the contact rods of the dendrograph to bear on the wood 
 formed by the tree two years previously. Thus, in 1920 holes were 
 bored through the wood of that year and of 1919 and contacts made 
 at the bottom of the cavities. 
 
 9. In general the awakening and growth of the terminal buds with 
 resultant elongation of leaders and branches begins in many trees some 
 time before enlargement of the trunk takes place. The period sepa- 
 rating the two may be no more than a week in Quercus agrifolia 
 and has been seen to be as much as 10 or 12 weeks in Pinus radiata. 
 Observations on the Parry spruce and Douglas fir show that the trunks 
 of these trees are enlarging at a time when the buds are in a very 
 early stage of enlargement. 
 
 10. In the single case in which dendrographs were attached to a 
 pine tree 1 meter and 8 meters above the ground, growth began coin- 
 cidentally at the two places in 1920. In the following year, however, 
 the dendrograph at the higher point on the trunk recorded enlargement 
 a few days before any action near the ground was made visible. In 
 February 1921 an auxograph was brought into bearing on the inter- 
 node of a pine tree 5 or 6 years old which had been formed in 1919. 
 The buds had made a growth of 4 or 5 cm., but no action had yet 
 begun in the internode. A second instrument was brought into 
 bearing on the middle of the internode formed in 1920 on another young 
 tree. Steady enlargement was in progress. 
 
 11. The embryonic layer of a tree is in the form of an inclosing sheath 
 terminating in the cones of the growing points. Activation of this 
 tract is generally initiated in the growing points. Swelling in the 
 cambium layer may be practically coincident with this awakening in 
 some trees. Cases are recorded in the present paper in which weeks 
 elapsed between the awakening of the buds and the enlargement 
 of the base of the trunk. Activation of the growing cells may be taken 
 to depend upon the localized food-supply, temperature, moisture, or 
 other factors.
 
 GROWTH IN TREES. 7 
 
 12. Estimates of the range of daily equalizing variations in a Mon- 
 terey pine taken from bearings on a thin layer of cork external to the 
 bast of a trunk which had ceased to grow for the season show that the 
 diameter might vary 1 part in 1,750. That a large share of this varia- 
 tion is due to changes in the hydration of the living cells is proved by 
 the fact that when bearings are taken on the woody cylinder of the 
 trunk internal to the growing layer the variation drops to 1 part in 
 8,750 of the diameter. The actual change in volume, in the first 
 instance calculated on the basis of a conical trunk 18 meters high and 
 35 cm. in diameter at the base, would amount to about 400 cu. cm., 
 of which not more than one-fifth, or 80 cu. cm., is attributable to varia- 
 tions in the wood. It is to be noted, however, that the change in the 
 volume of the wood may by no means be taken to represent the water 
 deficit in the wood. The woody mass is made up of box-like cells, 
 which may include a bubble of gas, the water forming no more than a 
 thin film on the wall of the cell and inclosing the gas bubble in the 
 condition of extreme water deficit. The withdrawal of water through 
 the walls of the cells, which are semi-rigid, increases the surface ten- 
 sion of the gas bubble, which results in a slight lessening of volume of 
 the whole mass, but in an amount that would constitute no more than 
 a small fraction of the total of the water loss. 
 
 13. Of 15 trees which were under dendrographic measurement in 
 1920, one each of Pinus scopulorum, Citrus aurantica, and Parkinsonia 
 microphylla made no enlargement during the year. Such occurrences 
 are to be taken into account in estimations of the ages of trees from 
 the annual layers. 
 
 14. The greatest daily equalizing variations were shown by Frax- 
 inus, Pinus, Picea, Pseudotsuga, and Juglans, and lesser variations 
 were displayed by Populus, Platanus, Fagus, Quercus, and Citrus. 
 No available facts furnish the basis of an adequate explanation of such 
 differences. 
 
 15. The final effect of rainfall shown within a few hours is to accel- 
 erate growth, but it has been repeatedly observed that actual shrink- 
 age may take place while the rain is falling. This action can not be 
 traced to any instrumental error. 
 
 16. Irrigation of the soil which had a moisture content of less than 
 6 per cent around the roots of a Monterey pine was followed within 
 24 hours by progressive enlargement constituting growth at the base 
 of the tree, and at a point 8 meters higher. The distance from the 
 absorbing surfaces of the roots through which the added water supply 
 must enter could not be less than 3 meters from the lower instrument, 
 and the influence of the added supply was within the day felt at the 
 upper instrument, 11 meters from the absorbing surfaces. It does not 
 seem possible that water could have been conducted through the 
 tracheids this distance within the given length of time.
 
 8 GROWTH IN TREES. 
 
 17. An irrigation test similar to the above was made with a small 
 California live oak (Quercus agrifolia). The results were even more 
 startling than those described for the pine. Within two hours the 
 dendrograph, which had its contacts with the tree at least 3 meters 
 from the absorbing surfaces, showed some enlargement, an action 
 which may be directly connected with the fact that the vessels in this 
 oak are numerous and large. 
 
 18. The irrigation experiments might be held to simulate the effects 
 of stream overflow which, if due to melting snows, would not be accom- 
 panied by any marked higher humidity. It is seen to result in the 
 formation of a tapering shell of wood which was as thick as the seasonal 
 formation at the base of the trunk, but which had but half this thick- 
 ness 8 meters higher up on the trunk. The layer of normal formation 
 was of practically identical thickness at the two places. 
 
 HISTORICAL. 
 
 The rate and course of growth in length of seedlings and plantlets 
 of various trees have been the basis of many measurements, and the 
 forester developed approximate methods for estimating the yearly or 
 seasonal increase in the height or diameter of trunks. An interesting 
 series of monthly measurements of a number of trees was made at 
 San Jorge, Uruguay, in 1885-1890. Evergreen trees, including 
 conifers, eucalyptus, and acacia, showed greatest increases in October, 
 a spring month, and least in July (midwinter), while deciduous trees 
 increase most in midsummer (December) and actually decrease in 
 girth in autumn (May). 1 Recently, also, some calibrations of the 
 variations in volume of trunks correlated with temperatures have 
 been made in New York. 2 The available data, however, did not re- 
 cord the daily and seasonal changes or include information by the aid 
 of which the activities of growing tips and branches might be correlated 
 with changes in volume of trunks and stems. 
 
 The most notable attempt to follow accurately the variations in tree 
 trunks previous to the instrumentation described in the present paper 
 was that of Mallock in 1917. He used an apparatus consisting essen- 
 tially of two plates of glass superposed, or an arrangement of prisms 
 in connection with a tape of invar passed around the tree. Vaiiations 
 in girth caused displacement of interference bands of light. Obser- 
 vations on such displacements, at frequent intervals, showed that 
 growth was greatest hi the early part of the day, that actual contraction 
 occurred in the afternoon, and that increases were closely related to 
 temperature and rainfall. 3 
 
 1 Hall, C. E. Notes on tree measurements made monthly at San Jorge, Uruguay, from Jan. 
 12, 1885, to Jan. 12, 1890. Trans. Bot. Soc. Edinburg, 18:456. 1891. 
 
 2 Trowbridge and Weil. The coefficient of expansion of living tree trunks. Science, 48 : 348-350. 
 1918. 
 
 * Mallock. A. Growth of trees, with a note on interference bands formed by rays at email 
 angles. Proc. Roy. Soc., 90, B, 186-191. 1919. Submitted Dec. 1, 1917.
 
 GROWTH IN TREES. 9 
 
 This ingenious method would enable the observer to detect changes 
 of 0.00005 inch in circumference, but as no recording devices are 
 provided the constant attendance of the observer was necessary. 
 Meanwhile my own results show that an actual amplification of 8 to 
 15 times the changes in diameter of the trunk is adequate for direct 
 observation and analysis. 
 
 Friedrich had previously used a device for recording increments to 
 the thickness of trees as early as 1905. 1 The tree was encircled 
 with a steel band on roller bearings, and the ends were attached to 
 both registering and recording arms. No cognizance was taken of 
 errors due to changes in temperature, and no results obtained with 
 this apparatus have been seen. 
 
 Some success having been attained in the measurement of the varia- 
 tions in stems such as those of the sunflower (Hehanthus) and in the 
 variations in volume of succulent stems such as those of Opuntia, 
 by the use of mechanical levers, it was found desirable to extend the 
 observations to trees. It was thought that accurate measurements of 
 the changes in volume of these massive structures might not only 
 give information of value on the subject of hydration and growth, but 
 that some light might be thrown on the problem of ascent of sap. 
 
 The attempt to measure the variations in large trunks, begun in 
 1918, raised many difficult mechanical problems. First it was obvious 
 that it would be practically impossible to hold the stem of any but 
 small trees rigidly in any position. This made it necessary to devise 
 means whereby the tree would support the instruments and carry 
 them with it as it swayed and leaned. It soon became evident that 
 such an appliance should consist of two parts; a base which would 
 remain firmly in whatever position near the horizontal it might be 
 placed about the trunk, and which would carry the more delicately 
 arranged members of the second part which would register variations in 
 diameter at some little distance from this base. 
 
 Two forms of base or support were devised and tested. One form 
 consisted of a rectangular frame built up of bands of wrought-iron 
 2 by ^ inches and of oak wood 2 by 2> inches, which could be 
 clamped about the tree tightly by means of an iron rod, including a 
 heavy turnbuckle. A heavy block of seasoned oiled wood at one end 
 formed a base for the levers and recorders and a wooden screw 30 cm. 
 long, working in a smaller threaded block hinged to the outer end of 
 the larger base block, extended to a point on the trunk several centi- 
 meters below and formed a brace which kept the block rigid in its posi- 
 tion with respect to the tree. Flexible supports carried a floating 
 frame which served to register variations in thickness. This form of 
 base was heavy, unwieldy, and by reason of the metal was subject to 
 temperature variations which might influence the record. 
 
 1 Friedrich, J. Zuwachsautograph. Centralb. fQr das gesammte Forstwesen. 31, pp. 456- 
 461. Nov. 1905.
 
 10 
 
 GROWTH IN TREES. 
 
 as a 
 
 The second and preferable form of base may be described in a phrase 
 belt of wooden blocks hinged together. Seasoned and oiled 
 
 blocks of redwood (Sequoia sempervirens) , 15 by 7 by 7 cm., were 
 bound together in a belt by pairs of galvanized strips of iron. Small 
 bolts passed through the ends of these strips and through holes near 
 
 FIG. 1. Earlier form of dendrograph with which all records previous to September 1920 were 
 made. This instrument takes a bearing from a prepared area on the bark of the tree by one end 
 of a email lever, the other end of which is connected with the short arm of a recording lever. Th 
 improved instrument includes a lever set, in which the bearing on the tree is made by a hor 
 zontally moving quartz rod, as shown in fig. 2. An encircling belt of wooden blocks serves as 
 base and support. Flexible wire standards, with a base of thin sheet metal, are clamped i 
 position on the wooden blocks, and screw clamps which slide up and down on the wire standarc 
 serve to hold the floating frame in a horizontal position. The entire apparatus is so adjusted tha 
 a contact rod on the opposite side of the tree ie held witfr gentle pressure against the tree and any 
 variation in diameter is then expressed by movements in the lever set.
 
 GROWTH IN TREES. 11 
 
 the end of the blocks were easily put in place or removed, so that any 
 number of blocks might be joined to form a support which would en- 
 circle a tree of any size. From 4 to 9 blocks were used in most of the 
 instruments. A wooden block of larger size, carrying an upright rod 
 10 cm. long as a support for the recorder, was used to close the support 
 or form the buckle of the belt. The actual fastening, however, con- 
 sisted of a pair of threaded rods extending from the large block and 
 resting in the slots of angle irons on the small end block. Nuts of 
 suitable form could be turned on these threaded rods until a suitable 
 tension had been put on the belt (see fig. 1). A long wooden screw, 
 working in a small block hinged to the outer end of the instrument base, 
 forms a supporting brace as in the other form of support. When such a 
 belt base is drawn tightly about a tree of the sizes measured, the eight 
 or nine blocks used adjust themselves to the irregularities of the trunk, 
 but in general assume a tangential position and press tightly on the 
 bark and cambium internal to it, but the total disturbance by such pres- 
 sure is small and does not affect the changes in the volume of the por- 
 tions of the trunk actually measured, a few centimeters higher. 
 
 The essential feature of the apparatus is the floating frame which 
 makes two contacts with the trunk. One such contact is made by a 
 set screw, carried by this frame, which may be turned to a point 
 where it makes a slight but firm contact on the trunk. The second 
 contact is made by the quartz-bearing rod of the lever-set carried on 
 the floating frame at a point diametrically opposite to the contact 
 screw. Any change of the trunk affecting the distance between the 
 end of the contact screw, which is immovable on the floating frame, 
 and of the sliding quartz rod of the lever system or set would be ex- 
 pressed in the movement of the pen lever which traces a line on the 
 graduated paper sheet carried by the revolving cylinder. 
 
 The first instruments were constructed at a time, during the Great 
 War, when it was impossible to procure the alloys which have a low 
 temperature coefficient. Floating frames of wood and iron were con- 
 structed in a U -shape. The curved ends of the U consisted of a bar 
 of wrought iron, 1 by ^ inches, fastened by bolts to the sides of the U, 
 which were of seasoned oak boiled in paraffin. The oak bars used for 
 the frames of the carriage tops were found suitable for this purpose and 
 (as they were 3 by 2 mm. in cross-section) are sufficiently rigid. The 
 instrument bar was a strap of iron with the ends turned at right angles 
 to be parallel to the wooden bars. These short arms are slotted so 
 that the instrument bar may be fixed in position at a suitable distance 
 from the trunk. Cold would cause the curved iron member of the 
 frame to be drawn toward the tree, and as the turned ends of the 
 instrument bars run from the tree their contraction by cold would 
 cause a movement which would tend to maintain an equal distance 
 between the two and leave uncompensated only the temperature varia-
 
 12 GROWTH IN TREES. 
 
 tion of the wooden side arms. As the temperature coefficient of such 
 wood is about 0.000054, or 3 times as great as that of brass, extensive 
 and difficult corrections were necessary. 
 
 The U-shaped floating frame was retained during the earlier stages 
 of development of the dendrograph, and this form has some desirable 
 features, especially when the record of a slowly growing tree is to be 
 obtained for a long period. Such frames have now been used in 
 securing records of growth of Pinus radiata No. 1 for two seasons; 
 however, the enlargement is at such a rapid seasonal rate that the 
 frames must soon be replaced. 
 
 The final form of the floating frame is that of a polygon constructed of 
 strips or bars of invar or bario, 15 to 30 cm. in length, 3 to 5 mm. in 
 thickness, and 12 to 15 mm. in width. These pieces have slots near 
 each end, about 5 to 8 cm. long, through which short bolts are passed. 
 When five to eight such strips are joined to form a suitable frame about 
 a tree, the nuts on these bolts are tightened and the joined parts are 
 held as rigidly as of one piece. One of the members of the floating 
 frame carries a block of metal welded to it and bored to receive the 
 contact screw which is provided with a set nut. The member of the 
 floating frame which is nearest the instrument block carrying the 
 recorder is bored to receive the small bolts which carry the lever set 
 designed especially for this instrument. 
 
 The essential feature of this lever set is a quartz rod, 3 or 4 mm. in 
 diameter, 7 or 8 cm. in length-, which slides in holes of the vertical 
 arms of the adjustable frame of the set. The outer end of this rod 
 is fitted with a slotted cap or guide by which its rounded end is kept 
 in place against the short arm of an L-shaped lever. The long arm 
 of this lever carries a pen of the type used on thermographs. The 
 dropped arms of the frame which carry the sliding quartz rod have 
 three pairs of holes, so that the rod placed in the lowermost holes en- 
 gages the short arm of the lever near its end, thus causing the least 
 amplification of its movement in the record, which is ordinarily about 
 10 times. The rod when placed in the middle pair of holes causes the 
 pen to move through an arc 15 tunes as great as the motion of the 
 rod, and when placed in the uppermost holes the bearing against the 
 short arm of the lever is so near the pivot that an amplification of 22 
 is made in the record. The actual amplification is of course tested for 
 each instrument. The metal parts of the lever set are of monel, since 
 this avoids corrosion and the construction (as shown in fig. 2) is such 
 that all of the necessary adjustments are made possible by sliding the 
 parts of the frame upon each other 
 
 The recorder is also of a design perfected for use with this instru- 
 ment. A strong clockwork is inclosed in a heavy case. The upwardly 
 projecting end of the msin arbor of the clock is fitted with a cap over- 
 jutting in such manner that, when in place, water coming down as
 
 GROWTH IN TREES. 
 
 13 
 
 rain does not enter the case. A circular table or base is fitted to the 
 cap, and a drum made of a pection of large brass pipe sits directly on 
 this fitting inside its raised rim, so that it may be removed without dis- 
 turbance of the clockwork. 
 
 The new feature of importance of this cylinder is the manner in 
 which the record paper is attached. The paper is 80 mm. in width and 
 
 FIG. 2. Improved dendrograph lever set. A, inner end of quarts rod in contact with prepared 
 surface on the bark of the tree. The outer end of the quartz rod is fitted with a metal guide which 
 engages the short arm of the recording lever at B. The long arm of the recording lever, D. 
 carries a pen which makes a tracing on ruled paper on a revolving drum. The horizontal member 
 of the frame C, which carries the recording lever, may be toward or away from the tree to adjust 
 the pen at any point on the paper record sheet. 
 
 ruled to millimeters. When placed on the drum the ends are thrust 
 through a slot 1 mm. in width and the free ends are creased on the 
 inside without further fastening. When the drum with the paper so 
 attached is set on its circular base the paper is properly in position 
 when its lower edge is hi contact with the rim of the base. A covering 
 as described below is placed over the recorder, but in any case actual 
 rain falling on it would mar only the record and could not damage the 
 instrument. 
 
 The floating frame, how r ever, is exposed to all features of the weather 
 and to the effects of sunlight which might cause its temperature to 
 vary from about C. to 25 C. during the growing season of the trees
 
 14 GROWTH IN TREES. 
 
 measured, and if the variations were to be recorded during the entire 
 year the range would be even greater. The change in dimensions of a 
 floating frame of invar arranged in the form of a polygon with a total 
 perimeter of 60 cm. may be estimated from the following data. The 
 temperature coefficient of this metal is 0.00000015 per degree, and the 
 daily range of ah 1 temperature does not vary beyond 25 C., usually 
 much less. The daily rise in temperature of this yoke, which would 
 tend to increase its radius and to make the daily shrinkage of the tree 
 appear to be greater than it really is, would therefore be found by 
 the following formula: 
 
 ., V (0.7 X 10 c) 600 
 
 in which E equals expansion and V the range of variation. E there- 
 fore is equivalent to 25 X 0.0000007 X 600 divided by 3.1416. The 
 possible enlargement of the diameter of the yoke, if the temperature 
 rose from 10 to 35 C., which would be a maximum, would be no more 
 than 0.0036 mm. Part of this is practically compensated by the 
 radially arranged contact screw of invar which projects inwardly 
 30 mm. It is to be seen that when this error is amplified 12 tunes it 
 could amount to no more than about 0.04 mm., which would not be a 
 discernible interval on the record. The use of invar or bario may be 
 taken to furnish a floating frame, the variation of which would be 
 negligible in measurements of variations in the trunks of trees. 
 
 One additional feature of the instrument yet remains to be described, 
 this being the devices by which the floating frame is kept in its hori- 
 zontal position around the trunk. This is accomplished by a series 
 of clamps and upright flexible wire supports. Sections of bronze wire 
 or bronze-coated steel wire, about 10 cm. in length, are fastened to a 
 foot or base of brass 3 by 5 cm. Such supports are placed in suitable 
 positions on the upper surfaces of the wooden blocks of the encircling 
 belt and fastened in place by clamps of proper size. Each upright 
 wire carries a small brass clamp which may be moved up and down and 
 fastened at any point. The free end of this clamp is slotted to receive 
 the flat members of the floating frame which are fixed firmly in place 
 by set screws. Adjustments of positions of the wire supports and of 
 the clamps on the members of the floating frame are made until the 
 last named is held in such position that the contact screw exerts a 
 small amount of pressure on the trunk, so that any variation will be 
 expressed by movements of the quartz rod of the lever set on the oppo- 
 site side of the tree. 
 
 The adjustment of the contacts is a matter of some nicety. A 
 broad chisel may be used to slice away the bark until a thickness of 
 not more than a millimeter remains outside of the living tissue, over an 
 area about equal to that which might be pressed lightly by a finger tip.
 
 GROWTH IN TREES. 15 
 
 Actual adjustment of an instrument in this manner is a work of about 
 an hour. During all of this time the recording lever has been kept 
 in a vertical position. It is now lowered until the short arm engages 
 the guide on the quartz rod and is in good contact. The recorder is 
 now swung around until the paper on the drum is brought against the 
 pen, being rotated to begin tracing on the proper day and hour. With 
 pens properly inked, a complete record- for a week may be obtained 
 without further attention. 
 
 Not all of the results cited were obtained with the instrument de- 
 scribed above, which has been in use only since September 1920, but 
 the earlier records have not been used in any manner in which their 
 faults might vitiate the general discussions and conclusions founded 
 on them. 
 
 THE DENDROMETER. 
 
 The records made by the dendrograph show the volume or diameter 
 of the tree at any moment and the variations which have taken place 
 in reaching these dimensions. Such observations are indispensable 
 to any searching study of the course and physical basis of the growth 
 procedure. It is also important to determine the total amount of 
 growth which may have taken place in a trunk during a season or a 
 period of years. Such an instrument would serve to check the detailed 
 records of the dendrograph and would have direct usefulness in the de- 
 termination of the increment in trees grown for timber. 
 
 An instrument of this kind, which might be read only at the be- 
 ginning or end of a season, could be constructed of common materials 
 without regard to the temperature coefficient of the members. Such 
 an instrument, known as a dendrometer, was designed in 1920 and a 
 number of models have been in attachment to trees since May of that 
 year. 1 
 
 The principle of an encircling wire carried by a number of plungers, 
 originally tested for the dendrograph in 1918, was utilized in the 
 construction of the dendrometer. Such a device was unsuitable for 
 the recording instrument, as it was impossible to secure a wire of 
 sufficient flexibility with a low temperature coefficient. As noted, how- 
 ever, this objection had no weight in the simpler instrument, which 
 was to be read at long intervals. The first assembly of this instru- 
 ment, consisting of a belt of blocks linked with strips of galvanized 
 iron 125 mm. long, 40 mm. wide, and 0.8 mm. in thickness, bearing 
 guides for five radially arranged plungers, was fastened to a Quercus 
 
 1 It is to be noted that the term dendrometer has been applied to instruments used by th 
 forester by which the diameter of trunks is taken by direct observation, the observer sighting at 
 the part of the trunk to be measured. See D. Bruce: A new dendrometer, Univ. of Calif. Pub., 
 3, No. 4, pp. 55-61, 1917.
 
 16 GROWTH IN TREES. 
 
 agrifolia, 75 cm. in circumference, on May 28, 1920. Spliced banjo 
 wires of silvered steel were run through the outer ends of these plungers 
 or contact rods, one end being anchored in such manner that slack 
 could be taken up and tension adjusted; the other end was taken around 
 a small pulley, one radius of which was prolonged by a pointer 15 cm. 
 long. The radius of the pulley was 0.5 mm. Five contact points 
 were arranged on the tree which would allow this instrument to show 
 variations in as many radii. Six months later the tip of the pointer 
 had moved through 110 cm. and as the amplification was 30, the actual 
 enlargement of the perimeter of the polygon made by the wire was 
 
 -5- cm., which was due to the action of the tree in 5 radii. This elon- 
 o 
 
 gation being of the circumference, the average elongation of a radius 
 would be represented by 
 
 iix^X 
 3 X 5 X 
 
 This would imply an enlargement of a millimeter in thickness. It 
 is to be noted that the observation was begun at a time when the tree 
 had made the greater part of its growth for the season. 
 
 After a series of trials of a wide variety of devices, a final design was 
 adopted in which the support was a narrow band of galvanized iron 
 or a belt of heavy wire bent in undulating folds, the ends being securely 
 brought together by slender threaded rods working in slotted angle- 
 irons attached to the ends of the belt. Sections of copper tubing or 
 copper rods, 15 cm., long, are bent into the form of an L. One arm, 
 10 cm. long, is flattended and perforated for attachment to the belt or 
 support. The other arm is in a position radial to the tree and the 
 spring-like action of the long arm presses its end gently against a pre- 
 pared spot in the bark. A pointer and dial are attached to the support 
 at the point where the ends are brought together. One end of a piece 
 of nickel wire, about 28 or 30 gage, is anchored to a post on the dial, 
 and the wire is led around the tree, passing through suitably smoothed 
 holes in the short arms of the copper arms or plungers, and the free 
 end is attached to the short arm of the pointer (fig. 3). 
 
 Adjustment of either end of the wire is made so that a delicate but 
 positive pressure is exerted by each plunger on the surface of the trunk 
 and the pointer is at zero, or at some datum point duly noted. Such 
 instruments are inexpensive, so that they might be used in large num- 
 bers in any serious attempt to measure increments of timber trees, and 
 would need very little attention. It is to be noted, of course, that they 
 may be subject to accidents from falling branches or large animals; or,
 
 GROWTH IN TREES. 
 
 17 
 
 if the wire has been kinked in adjustment, breaks may occur after 
 a few days at ordinary tensions. 
 
 FIG. 3. One form of the dendrometer. An encircling band of galvanized steel strip is brought 
 together at B and rests upon wooden blocks bearing on the bark at F, F, F, F, etc. An encircling 
 wire pasbes through suitable holes in flexible arms attached to the supporting steel strip. This 
 wire is anchored to a post on the inner side of the dial, the other end being attached to the short 
 arm of the indicator at A. The enlargement which has taken place has pressed the flexible arms 
 outward, pulling on the wire to such extent as to cause the indicator point to move from zero at 
 the bottom of the scale to "4." 
 
 MEASUREMENTS OF PINE TREES. 
 
 The Monterey pine (Pinus radiata) is native to the maritime climate 
 of the fog belt of the Monterey peninsula and the slopes of the Santa 
 Lucia mountains to the southward ; and, as numerous trees of all ages 
 were available on the grounds of the Coastal Laboratory at Carmel, it 
 was selected for an intensive study of the growth of the pines. 
 
 This tree is characterized by extremely rapid growth, both in length 
 and thickness, and does not survive to an age of more than about 80 
 years. The staminate and pistillate flowers are matured late in 
 January and the pollen is scattered in February. Elongation of the
 
 18 GROWTH IN TREES. 
 
 tips of the branches, especially of young trees, begins about this time 
 and such growth may continue until September, according to Dr. 
 Forrest Shreve, 1 who reports that records of elongation of as much as 
 10 feet of the leaders of young trees are in existence. Dr. Shreve has 
 also described the features of the trunk, but an example examined by 
 the author will serve to illustrate the structure of such trunks. This 
 tree was about 12.5 meters in height, 15 cm. in diameter a meter above 
 the ground, and had 12 layers of wood in the heart and 18 in the lighter- 
 colored sapwood. The heaviest increments to the trunk, according 
 to Dr. Shreve, occur in the period of development between 10 and 20 
 years of age, at which time very heavy layers of wood may be formed. 
 
 Dendrographic measurements of the variations and growth of jthe 
 trunks of nine trees in the grounds of the Coastal Laboratory have 
 been made since September 1918. A continuous record of the ba^al 
 section of the large tree upon which the observations were begun has 
 been kept since that time, and a second instrument was attached to 
 this tree 9 meters above the ground in March 1920, so that a double 
 record for an entire season is now available. 
 
 The seasons in the region in which the Monterey pine grows are 
 indeterminate as to frost and temperature features, but the rainfall 
 occurs in the winter and growth is seen to depend upon the soil supply 
 of water and the rising temperatures, with the result that enlargement 
 of the trunks continues until the soil moisture around the absorbing 
 roots is depleted until it forms no more than 6 to 10 per cent of the total 
 weight. 
 
 The present studies have been devoted chiefly to changes in volume 
 of trunks and so many technical problems have been encountered that 
 no attention has been paid to the features of development of the cam- 
 bium inclusive of the periods of cell-division, of xylem formation, of 
 phloem formation and collapse, of rifts and stresses in bark, or seasons 
 of activity of roots. Important contributions on these subjects have 
 been made recently by L. Knudson, 2 H. P. Brown, 3 and I. W. Bailey. 4 
 
 It was thought advisable, however, to make some measurements of 
 the changes in length and thickness of leaders and young stems and 
 this was done both in the early part of the season and in the autumn. 
 
 1 Shreve, Forrest. Stem analysis and elongation of shoots in the Monterey pine. Carnegie 
 Inst. Wash. Year Book for 1919, pp. 88 and 89. 
 
 2 Knudson, L. Observations on the inception, season, and duration of cambium development 
 in the American larch (Larix laricina Du Roi Koch). Bull. Torr. Bot. Club, 40: 271-293, June 
 1913. 
 
 3 Brown, H. P. Growth studies in forest trees. I. Pinus rigida Mill. Bot. Gaz., 54: 386-402, 
 1912. II. Pinus strobus L. same journal, 59: 198-240, 1915. 
 
 4 Bailey, I. W. Phenomena of cell-division in the cambium of arborescent gymnooperms and 
 their cytological significance. Proc. Nat. Acad. Sci., 5: 283-285, 1919. 
 
 . The cambium and its derivative tissues. II. Size variations of cambium initials in 
 
 gymnosperms and angiosperms. Amer. Jour. Bot., 7:355-367, 1920. III. A reconnaissance 
 of cytological phenomena. Amer. Jour. Bot., 7:417-434, 1920.
 
 GROWTH IN TREES. 19 
 
 The daily procedure in elongation during September may well be 
 illustrated by the following excerpts from the notes: 
 
 The temperature of the air varied between 13 and 22 C. during the greater 
 part of the time, this equable feature of the climate being accompanied by 
 fogs and high humidity. 
 
 The record of the first day was made on a 24-hour clock cylinder to give 
 opportunity for minute analysis. This showed that the stem contracted as 
 much as 0.3 mm. in the forenoon period, which in this case was clear and sunny, 
 and in the periods ending the next morning an increase of 12 mm., or a net 
 total of 8 mm., was made. This behavior was duplicated in the following 10 
 days, during which time the period of elongation of the stem came to a close. 
 Greater activity being displayed by the laterals, attachment was transferred 
 to one of these and a similar procedure was recorded for 7 days, at which time 
 it also came to a state approaching quiescence on September 8. 
 
 On October 15 the instrument was attached to the lateral of another plant 
 continuously in the shade and the record for the succeeding 20 days shows 
 daily variation, including shortening at midday, but with little total growth 
 except on days on which the temperature of a large trunk rose to 17 or 18 C., 
 or the air was humid by the effect of fog or rain. Such a case was produced by 
 fog on October 21 and 22, which were followed by a period of a week of clear 
 days with trunk and air temperatures not widely different in a range from 15 
 to 22 C. during which time the daily variations did not result in any actual 
 increase. 
 
 The influence of humidity and water supply is illustrated still more strikingly 
 by the behavior of No. 5, an unbranched plantlet 40 cm. high, probably about 
 16 months old. Attachment was made to the tip of this plant on September 
 8 and on the two succeeding days a midday decrease and a following larger 
 increase of 0.5 mm. or less were displayed. Beginning at midday on the 
 llth, rain fell continuously for 50 hours and an enormous acceleration ensued. 
 The temperature during this time was 19 to 20 C. The total increase during 
 this two-day period was over 10 mm., which was 5 or 6 times the previous rate, 
 in cool, dry days and cooler nights. On the day following the rain the increase 
 fell to 2.5 mm., after which the daily program of elongation and shrinkage 
 followed, with a net increase, however, of 2.5 mm. in 13 days, the rate diminish- 
 ing on September 28, at the end of this period, which probably soon passed 
 into the condition already described for No. 3. This record illustrates 
 markedly the accelerating effect of humidity on growth and suggests that 
 warm rainy periods of even a few day's duration may have a permanent effect 
 on the structure of the trunk. 
 
 These features are in accordance with a procedure which has been studied 
 and described in great detail in a large number of morphological types of 
 plants. Excessive or maximum water-loss during the daylight period lessens 
 the rate and amount of enlargement in growing stems and causes fluctuations 
 in volume of quiescent ones. 
 
 It is to be noted that the imbibitional conditions in stems a year old are 
 much different from those of large trunks. Thus, in such a stem the epidermis 
 is still unbroken, the cortex is chlorophyllose, over a millimeter in thickness, 
 and the numerous long leaves, which still are present, may withdraw a large 
 amount of water. The growing layer is nearly as thick as the cortex, while 
 the central pith is 3 or 4 mm. in diameter, the rays through the wood being 
 much in evidence. One-third of the diameter of a stem 24 mm. in thickness is 
 thus made up of thin-walled cells in a high state of hydration and in a condition 
 in which the water balance of the system may be quickly modified by evapora- 
 tion or temperature changes.
 
 20 GROWTH IN TREES. 
 
 The measurements in the first series were made by bringing a modified 
 auxograph lever in contact with the upright leader of a young pine which had 
 been surrounded by a platform and held rigidly in position. The net gain of 
 the daily fluctuations during the whole of August amounted to nearly a milli- 
 meter in thickness. .Now ensued a period of high fogs which during 3 days 
 equalized temperatures and humidity, reducing the daily variation, but 
 resulting in no increase. Finally, on September 5, rising temperatures and 
 humidity had the effect of producing a net gain which amounted to about 0.5 
 mm. before a rain came disarranging the clock-work of the recording cylinder. 
 Two days after this rain the instrument was again put in order and during 
 the following 2 weeks a daily increase in diameter was recorded which, on 
 September 27, had produced a net thickening of about 2 mm. The regis- 
 tration was discontinued for 2 weeks, but was resumed on October 15. The 
 increase had evidently continued during the interval, but was now coming 
 down to a minimum, as the net thickening in the following 2 weeks, termi- 
 nating October 29, was about 0.5 mm. 1 
 
 Further observations on the variations of young stems were made in 
 the autumn of 1920. A small tree, No. 8, 8 or 9 years old, about 
 3.5 meters in height, was bent over so that the terminal leader which had 
 been formed by the growth beginning in February was held rigidly 
 on a block of wood, in such manner that the vertical swinging aim of 
 an auxograph might rest directly upon it. Another tree, No. 9, 5 years 
 old, about 2.7 meters in height, was similarly arranged but with the 
 internode formed during the previous year under measurement. 
 
 The record of No. 8 shows that enlargement in diameter had ceased 
 on September 17 and that progressive shrinkage was recorded during 
 the following 10 days. Irrigation was followed by some increase. 
 The daily variation was not so great in the older internode of No. 9, 
 and irrigation was followed by a more pronounced and long-continued 
 enlargement. 
 
 The auxographs were again brought into bearing at the same places 
 on the internodes of these two young trees for 10 days beginning 
 February 24, 1921. The terminal internode of No. 8 was now nearly a 
 year old and the buds at its tip had made an elongation to about 5 to 
 10 cm. during the previous month. The internode of No. 9, upon 
 which measurements were made, was now nearly 2 years old. The 
 buds at the tip of the terminal internode above it had made an elonga- 
 tion of 3 to 5 cm. It was soon seen that the two-year-old internode of 
 No, 9 had not awakened, as the pen traced a straight line, the soil 
 water supply being sufficient to maintain the water balance in the wood. 
 The one-year-old leader of No. 8 was already in course of growth, and 
 during the 10 days of the record showed an increase of 0.8 mm. in 
 thickness. A slight depression of the rate of growth occurred in the 
 midday period, especially on days of highest temperature. 
 
 Passing from these measurements to variations in pine trunks, more 
 complex conditions are encountered. In securing dendrographic 
 
 1 The records upon which the above statements are based were interpreted erroneously, 
 as stated in my account of 1919. See Carnegie Inst. Wash. Year Book for 1919, p. 76.
 
 GROWTH IN TREES. 21 
 
 measurements the old, flaking outer cork layers of the bark were cut 
 away and bearings were taken on the thin layer formed in the previous 
 year, which had not yet become heavily browned. Internal to this is 
 the bast, which forms a layer about 2 mm. in thickness, and internal 
 to this is the cambium layer. Growth or permanent enlargement would 
 depend upon the division, enlargement, and differentiation of the 
 elongated, spindle-formed elements of the cambium. 
 
 While new cells are being formed by division, and these are under- 
 going the enlargement constituting one of the main features of growth, 
 these cells form a very thin layer external to the woody cylinder. 
 This woody cylinder, with its closed systems of tracheids or wood- 
 cells, is the conducting system by which solutions pars from the roots 
 to the transpiring surfaces of the leaves. 
 
 The rate of water-loss from the leafy surfaces may vary widely 
 during the course of the day as a result of changing temperatures of 
 the air, while the temperature at which water passes into the trunk at 
 its base changes but slowly, and chiefly in response to eoil-moisture 
 proportions. It is obvious that such relations between absorption and 
 loss of water may result in more water being given off during any 
 period than is taken in. Such excessive transpiration can, of course, 
 occur only from a balance or surplus, and this accumulated reserve, 
 occupying the entire trunk of the tree, may be very great. Any 
 lessening of its volume, however, would cause variations in the dimen- 
 sions of the trunk to an extent determined by a set of conditions which 
 need not be elaborated here. 
 
 The most valuable dendrographic data, so far available, are those 
 obtained from the Monterey pine. The separate trees, five in number, 
 to which dendrographs have been attached are briefly described as 
 below: 
 
 No. 1 is about 25 meters in height, bearing only short, thin branches, 
 with the trunk 40 to 44 cm. in diameter a meter above the ground. 
 Cores taken out by increment borers show 28 well-defined layers or 
 "annual rings." The radial increment the first year was 14 mm., and 
 varied from 2 to 5 mm. in the succeeding ten layers, which may not 
 safely be taken to represent annual formations. The second series of 
 ten layers has a total thickness of 62 mm., the separate layers varying 
 from 2 to 10 mm., the thinner ones being in all probability formed as 
 the result of autumnal rains, such as occurred in 1918. The total of 
 the 11 outermost layers amounts to 60 mm. of radial thickness, varying 
 from 2 to 9 mm. in the separate layers. Thus, on the basis of experience 
 described below, by which the tree after having formed a layer 5 mm. 
 in thickness in the early part of 1920 was awakened to form a second 
 layer of equal thickness by irrigation, it is assumed that the layer 2 mm. 
 thick interior to the layer of 1919, which is 8 mm. in thickness, resulted 
 from a rainfall of 5 inches early in September 1918. Formation of a
 
 22 GROWTH IN TREES. 
 
 layer 3 mm. in thickness had taken place during the first half of the 
 season in that year. Of the 31 layers or rings of this tree, one 'was 
 added by irrigation in 1920, one has the appearance of resulting from 
 autumnal rains in 1918, one very thin one was probably formed under 
 such circumstances in 1907, and another in 1904. The tree may 
 therefore be considered as being 27 years old at the beginning of the 
 season of 1921. 
 
 During 1920 a second instrument was placed on the trunk, 8 meters 
 above the ground. Tree No. 2 of this species was about 18 meters in 
 height and 40 cm. in diameter near the base, with heavier branches 
 than No. 1, and stood on a sandy slope facing northward. A wide 
 variety of devices was tested on the instruments attached to this tree, 
 so that no continuous record, such as that which has been obtained 
 from No. 1, was obtained. 
 
 Monterey pine No. 6 was the smallest tree of this species to which the 
 dendrograph with floating frame was applied. It was about 10 meters 
 in height, 16 cm. in diameter near the ground, and stood on a north- 
 facing slope in position where the direct sunlight did not strike the 
 ground, which therefore remained at a lower temperature and with a 
 higher moisture content than the other trees. The presence of 20 
 rings or layers indicated an age of 17 years. The layer formed in 1920 
 had a thickness of 3 mm., which was equivalent to that of 1919, and 
 the secondary layers of 1907 and 1904 were plainly apparent. 
 
 No. 7 was about 14 meters in height and 35 cm. in diameter near the 
 base. Observations on this tree were confined to dendrographic 
 measurements of the woody cylinder from bearings made at the bottom 
 of borings extending through the wood of the previous year. Tem- 
 peratures of the outer layer of the trunk and of the heart were also 
 taken by mercurial thermometers. This tree stood on a north-facing 
 slope of a "fog channel" near No. 6, which was exposed to similar 
 conditions. 
 
 The most obvious points of interest in the growth program of each 
 year are those which concern the dates of awakening and cessation of 
 growth of terminals and of the trunk. 
 
 Elongation of terminals of No. 1 began early in February 1919, but 
 no enlargment of the trunk was measurable until March 30. A 
 period of low relative humidity and high temperature resulted in no 
 increase in diameter of the trunk between May 29 and June 6, after 
 which enlargement took place at a low rate for a few days, alternating 
 with periods in which only reversible variations were discernible. 
 This later phase of growth might be identifiable with an after develop- 
 ment of phloem, such as has been described by Brown 1 in Pinus 
 strobus. The total net accretion on the diameter measured by the den- 
 
 1 Brown, H. P. Growth studies of forest trees. Bot. Gaz., 59:237. 1915.
 
 GEOWTH IN TREES. 23 
 
 drograph was 9 mm. and the thickness of this layer (laid down in 1919) 
 taken from a boring on another diameter, in January 1921, was about 
 8 mm. 
 
 Heavy rains beginning on November 26, 1919, were followed by an 
 increase beginning on November 29, which continued until De- 
 cember 14. A similar slight increase following rain took place early 
 in January and late in January. 
 
 The instrument was reset on February 9, 1920, and a second one 
 reached by a scaffolding attached at a point 8 meters above it, both 
 making a record in which the variations in diameter were amplified 
 8 times (see fig. 4). The circumference of the trunk at the upper in- 
 strument was 100 cm. as compared with 130 cm. at the lower one. 
 The levers of both instruments were set to give an amplification of 
 8 times, so that it was possible to make direct comparisons of the ac- 
 tion of the trunk in the two places. The bark in both cases was thinned 
 so that the contacts were made on layers of cork not more than a 
 millimeter in thickness. The bark at the base of the tree was heavy 
 and was coming away in flakes, while that at the upper instrument 
 had begun to show only shallow rifts and was not more than 3 or 
 4 mm. thick at any place. Thermometers thrust under the bark on 
 the north side of the trunk showed temperatures as low as 6 C. on the 
 date mentioned and as low as 8 C. on March 30. 
 
 Some enlargement of the same type followed rain March 18 to 22, 
 but this was followed by a period of reversing variations, and not until 
 April 7 did a continuing enlargement begin which showed an initial 
 rate slightly greater than that at the uppermost instrument, which 
 began on the same day (fig. 5). 
 
 As this manuscript is being completed, the records for the early 
 part of 1921 are available. They show that the tips of the branches 
 on young and old trees began to grow about mid-January, and that the 
 enlargement of the upper part of the trunk of this tree showed en- 
 largement on the 27th of January, 2 days earlier than any increase 
 of the lower part of the trunk. Action in the two places was syn- 
 chronous in 1920, but did not begin until 2 months later than the 
 awakening of the tips of the branches. No attempt has yet been 
 made to correlate these facts with the activities of the roots, but the 
 observations of W. B. McDougall are to the effect that growth of the 
 roots begins quite early in the season and that it depends largely upon 
 moisture and temperature. 1 
 
 As in the previous year, a period of reversible variations began late 
 in May 1920, which continued until July 2, at which time the soil 
 moisture content had come down to 5 to 7 per cent. The total accre- 
 tion at the base of the tree was slightly less than 3 mm., slightly 
 
 1 McDougall, W. B. The growth of forest tree roots. Amer. Jour. Bot., 3:385-392. 1910.
 
 GROWTH IN TREES. 
 
 FIG. 4. Monterey pine No. 1, with dendrographs attached near the ground and at 
 a height of 9 meters.
 
 GROWTH IN TREES. 
 
 25 
 
 greater than 2 mm. at the upper instrument, differences which might 
 be seen in comparison of different diameters at any part of the trunk. 
 This layer showed a thickness of 4 mm. in the boring on a different 
 radius, on the lower and upper part of the trunk. 
 
 A number of tile pipes were now sunk in the soil in an area around the 
 tree, so that water might be conducted to the absorbing roots and 3,000 
 gallons of water were poured into these holes on July 1, 1920, with the 
 result that an enlargement was visible a day later, which was slightly 
 
 MAY 3 1920 
 
 FIG. 5. Dendrographic records of the changes in the trunk of a Monterey pine made by the two 
 instruments attached to No. 1, as in fig. 4. Record A is from Ihe lower part of the trunk and B 
 from the higher point, for the week beginning May 3, 1920. The sheet is marked into 6-hour 
 periods and the spaces represent 10 mm.; the actual changes in the trunk being X 8. Enlarge- 
 ment and partially equalizing daily variations are displayed. 
 
 28 1320 
 
 JUNE 28 1920 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 _ 
 
 ~ - 
 
 - 
 
 ' 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ^ 
 
 gois 
 
 wule 
 ive 
 
 Xo S 
 
 A m 
 
 jrmr 
 
 ft 
 
 
 
 
 
 FIG. 6. Equalizing daily variations of trunk of Monterey pine No. 1 for week beginning June 
 28, 1920. Application of water to soil around roots after 6 p. m. on July 2 was followed by upward 
 course of record lines from both instruments. Variations X 8 on 10 mm. scale. 
 
 greater at the lower instrument (fig. 6). Additional water was given 
 on each of the 2 days following, and enlargement continued at the upper 
 instrument until about August 16. During this period of 16 days an 
 enlargement of 2 mm. in diameter had taken place at the upper 
 instrument, 9 meters above the ground, and of 4 mm. at the lower 
 instrument, 1 meter above the ground (fig. 7). Enlargement at the 
 base continued until September 15, at which time a further thick- 
 ening of 2 mm. had taken place, making a total thickening of 9 mm. 
 at the base. Both measurements were in agreement with borings 
 taken in January and February 1921. Then followed a month of
 
 26 
 
 GROWTH IN TREES. 
 
 reversible variations with some slight increases on both places on the 
 trunk following a rain on October 14. Again some increases occurred, 
 beginning on November 16. Similar period of increase occurred in 
 December. No actual seasonal or winter shrinkages of the stem at 
 either point could be detected. 
 
 Very interesting occurrences of this sort, however, were observed in 
 connection with rains. On April 15-16, December 21-23, 30-31, 
 a continuous enlargement of the trunk took place which would be 
 wholly or almost wholly lost on the sunny day following. 
 
 AUG. 16 1920 
 
 
 8) 
 
 
 H 
 
 
 B 
 
 M 
 
 g 
 
 M. 
 
 tiA 
 
 M 
 
 
 
 
 
 
 
 f 
 
 - 
 
 ~~^ 
 
 . *-" 
 
 ^ 
 
 s, 
 
 
 
 
 "~N, 
 
 
 
 . 
 
 
 
 f 
 
 n 
 
 
 v 
 
 X^x 
 
 ""* 
 
 
 s 
 
 
 
 s^ 
 
 
 
 ' " 
 
 
 
 
 
 
 
 
 
 
 
 
 ^_ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 FIG. 7. Dendrographic record of the variations of lower and upper parts of trunk of Monterey 
 pine No. 1 at end of period affected by irrigation. 
 
 The present record is closed on January 27, 1921, at which time the 
 staminate flowers were nearly mature and the terminal buds were 
 beginning to swell, and some actual enlargement of the trunk had 
 begun and was still in progress on January 31. 
 
 During 1920 the basal part of the trunk had shown a total enlarge- 
 ment of nearly 9 mm. in diameter, and the section 8 meters from the 
 ground about 6 mm. The accretion of 1920 appeared in borings at the 
 base of the tree as two layers in two cores 5 and 4 mm. in thickness, 
 when measured at the end of January 1921. The outer layer may be 
 taken as representing accretion following irrigation, which, it may be 
 suggested, may have been largely in the phloem. The borings at the 
 higher point snowed two layers, 4 and 2 mm. in thickness. 
 
 Awakening of buds took place several weeks before enlargement of 
 the trunk began in 1919 and 1920, but in 1921 growth of both kinds 
 was apparent the last week in January, nearly two months earlier than 
 the observed dates of enlargement of trunks in previous years. 
 
 The variations of a younger tree were sought by the attachment of 
 an instrument to Monterey pine No. 6 on February 12, 1920. This 
 tree may be identified as beginning in 1904, as it made a second layer 
 of wood in its first year and shows the extra formations in 1907 and 
 1918. The floating frame of the instrument was of invar, the levers 
 being set at first to amplify 5 and later to 15 times. The trunk had a 
 diameter of 18 cm. and the first discernible enlargement was on
 
 GROWTH IN TREES. 
 
 27 
 
 March 16, after which acceleration carried growth to a maximum rate 
 in the last 10 days of April. The rate now slackened and growth 
 ceased about June 1, with a total increase of 4.5 mm. in diameter. 
 
 A rain on June 14 was followed by some growth in the following 
 week, after a period of reversible alterations ensued. Not until late 
 in July did a slight enlargement recur and a similar impulse was re- 
 corded at the end of August (fig. 8). No further increase could be 
 detected, but a shrinkage began on October 11 which continued until 
 
 FIG. 8. Dendrographic records of Monterey pine No. 6, with no growth in week of March 1, 
 1920, beginning growth in week of March 22-29, vigorous enlargement in week April 12-19 daily 
 equalizing variations of wide amplitude in week of June 28-July 5, and reduced variations late in 
 September. Variations X 5 on scale of 10 mm. intervals. 
 
 the instrument was dismounted a week later. A total increase of 
 5 mm. had been recorded. It is to be noted that the terminals and 
 tips of the branches had made a growth of several centimeters when 
 the observations were begun, and that such elongation must have 
 started about two months prior to the increase in the trunk. 
 
 Measurement of another pine (Pinus chihuahuana) , on the slopes 
 of the Santa Catalina mountains, an isolated range near the Desert 
 Laboratory, gave a set of results under conditions different from those 
 afforded by the indeterminate seasons of the coastal climate. A tree 
 40 cm. in diameter, in the lower edge of the pine belt at about 2,000 
 meters, was selected for observation. This location is characterized 
 by a coarse granitic soil, winter and mid-summer rainfall; minimum 
 air temperatures of 8 C. and summer maxima of 40 C. are of record.
 
 28 
 
 GROWTH IN TREES. 
 
 This tree stood about 4 miles from the base of the mountain and the 
 instrument was transported this distance by pack animals and put in 
 action on April 4, 1918, being visited weekly until the end of October. 
 The record showed some enlargement, beginning April 14, with a 
 cambium temperature of 13 C., with readings as high as 28 C. in the 
 following 10 days. When observations were taken on April 23, the 
 temperature of the cambium was 10 C. and enlargement had ceased. 
 A slight swelling occurred May 13-20. On May 22 a shrinkage began 
 
 13 1919 
 
 MAY 28 1919 
 
 FIG. 9. Dendrographic records of Chihuahua pine, with variations X 5 on 10 mm. intervals. 
 Some enlargement shown in week beginning April 15, 1919; shrinkage during week beginning 
 May 20; enlargement in week beginning May 28; daily equalizing variations of wide amplitude 
 in week beginning June 13 ; reduced variations and shrinkage in week beginning July 11 ; increased 
 variations and actual increases in diameter in week beginning August 16, and reduced daily 
 variations in late October. 
 
 which in 6 days amounted to 1 nun., or half the total increase during 
 the previous two months. Increase began on May 28, which amounted 
 to about 2 mm. on June 14, at which time equalizing variations began 
 at tree temperatures of 23 to 27 C., which continued until June 28. 
 Now, in the extreme hot mid-summer, shrinkage began which con- 
 tinued until July 20, or until about 3 weeks after the summer rains 
 began. During this time a shrinkage of about 2 mm. had ensued, 
 which was equivalent to about three-fourths of the gain up to this 
 date. A period of increase, ending August 23, resulted in a gain of
 
 GROWTH IN TREES. 29 
 
 5 mm., of which nearly one-half was lost in the last week of August. 
 Another slight swelling began September 14, terminating October 5, 
 after which equalizing daily variations occurred until the instrument 
 was dismounted October 22 1 (fig. 9). 
 
 The total enlargements amounted to about 10 mm. and the total 
 shrinkage during the season to about- 5 mm. It is obvious that the 
 woody layers formed in such an interrupted cycle of growth must be 
 difficult of interpretation by the observers who seek to obtain the 
 history of the tree from its "annual rings." Dr. Shreve has found 
 that individuals of this species form two such rings in locations at 
 slightly greater altitude but similar climatic conditions. 2 
 
 A dendrograph was attached to a yellow-pine tree (Pinus scopulorwri) 
 at the Fort Valley Forest Experiment Station near Flagstaff, Arizona, 
 late in April 1920. This tree was about 45 cm. in diameter and had 
 apparently ceased growth or was quiescent during this season. No 
 permanent change in diameter amounting to as much as a millimeter 
 occurred during the summer. Equalizing variations were marked, 
 however, during the latter half of July, after which the record showed 
 but little variation. Mr. G. A. Pearson, in charge of the Experiment 
 Station, reports that this tree showed some growth of branches and 
 terminals in 192 1. 3 
 
 A dendrograph was installed on the basal section of a yellow pine 
 (Pinus ponderosa) at the Alpine Laboratory, which made a record 
 from June 5 to September 15, 1920. Mr. Loftfield, who was in charge 
 of the instrument, reports that this tree was nearly 36 cm. in diameter 
 and that it stood on an east-southeast slope near the Douglas fir which 
 was also measured. Thermographic and hygrographic records were 
 obtained which pertain to both trees. As the instrument was set to 
 amplify 15 times, the daily equalizing variations appeared very marked 
 at the beginning, amounting to as much as 0.5 mm. in diameter daily. 
 An increase in diameter was noticeable on June 14, on which date an 
 inch of rainfall was noted, but this was only a temporary increase, as 
 equalization followed. A week later the buds awoke and disturbances 
 of the daily variation ensued. The branches reached full length early 
 in July and the leaves full size by the middle of the month, but not 
 until a month later (August 12), in a period of heavy rains, did an 
 increase take place. This continued until September 4, and during 
 this period of 23 days a net enlargement of nearly 2 mm. in diameter had 
 taken place, after which some shrinkage accompanied the daily 
 
 1 The above statements are to be taken in correction of the preliminary notice on the growth of 
 the Chihuahua pine in Carnegie Inst. Wash. Year Book for 1918, p. 75. 
 
 2 Shreve, F. The density of stand and rate of growth of Arizona yellow pine as influenced by 
 climatic conditions. Jour. Forestry, 15:695-707. Oct. 1917. 
 
 3 Pearson, G. A. The relation between spring precipitation and height-growth of western 
 yellow pine saplings in Arizona. Jour. Forestry, 16: 677-689. 1918. Boerker, R. H. Rela- 
 tion between height-growth of larch seedlings and weather conditions. Jour. Forestry, 16:861- 
 870. Dec. 1918.
 
 30 GROWTH IN TREES. 
 
 variations. The effects of humidity and temperature will be presented 
 in a later section. A core, taken from this tree by Dr. A. E. Douglass, 
 showed 74 layers or rings which varied from 1 to 5 mm. in thickness, 
 that for 1918 and for 1919 being about the same thickness as the 
 measurement for 1920 just given. 
 
 MEASUREMENTS OF A SPRUCE AND A FIR. 
 
 The Douglas fir (Pseudotsuga taxifolid), at the Alpine Labora- 
 tory on the slopes of Pikes Peak to which the dendrograph was 
 attached, was nearly 36 cm. in diameter and the instrument had 
 an amplification of nearly 16 times. The buds were developing 
 rapidly when observations were begun on June 17, at which time in- 
 crease of the diameter of the trunk was visible in the daily variations. 
 Growth was already in progress. The increase continued at a low 
 rate until July 21, at which time a total gain of 2 mm. in diameter 
 had been made. After some days of equalizing variations, with 
 temporary swellings consequent upon rains, an increase began August 
 11, which continued until the 22d, making the total accretion for the 
 season 2.6 mm. The shrinkage which ensued during the first half of 
 September reduced this total to 2 mm. 
 
 The only continuous record of the growth of this tree which had been 
 made previously is that by Mr. A. Mallock, who measured variations 
 in the girth of a tree which had a circumference of 33^ inches, by 
 means of an invar tape connected with glass prisms arranged to observe 
 movements of interference bands. These observations were made 
 July 5 to July 16, 1917, in England. It is not known whether any 
 growth had taken place earlier in the season, but a shrinkage was in 
 progress during the first 3 days of the observations, after which en- 
 largement began, and continued at a varying rate during the next 8 
 days. Slackening in the rate of growth occurred during the midday 
 period, and the increase was most rapid at night and following rains. 1 
 
 The actual beginning of growth of the trunk was not observed, but 
 probably not much had taken place before the record began, as the 
 buds were just opening. The record of this fir is to be compared with 
 that of a blue spruce (Picea pungens), which was measured by an 
 instrument in the hands of Mr. C. F. Korstian. This tree is on the 
 Cottonwood nursery grounds, 25 miles southeast of Salt Lake City, at 
 an elevation of about 2,250 meters. This tree was 38 cm. in diameter 
 and enlargement was in progress and the buds were opening on June 7. 
 The course of growth was similar to that of the Douglas fir, and as it is 
 being described in an article by Mr. Korstian, in the Botanical 
 Gazette for June 1921, it will not be repeated here. 
 
 1 Mallock, A. Growth of trees, with a note on interference bands formed by rays at small 
 angles. Proc. Roy. Soc., 96 B (see especially p. 193), 1919.
 
 GROWTH IN TREES. 31 
 
 GROWTH OF THE CALIFORNIA LIVE OAK. 
 
 The California live oak (Quercus agrifolia'), which is* one of the 
 commonest of the oaks of the Pacific slope and in the region of the 
 Coastal Laboratory, is a small tree with trunks 25 to 50 cm. in diameter. 
 The leaves of one season remain on the tree until those of the next 
 season are unfolding, which in this region begins early in February. 
 The first indication of awakening activity is the elongation of the 
 leafy branches which may occur in some individuals 2 or 3 weeks earlier 
 than in others a short distance away. As will be seen from the records 
 discussed below, enlargement of the trunk began in March, somewhat 
 earlier than in the Monterey pine in the same locality. 
 
 Measurement of this species includes one feature widely different 
 from the pines, in that the bark remains alive and turgid until it 
 reaches a thickness as much as 5 cm., and it is upon the surface of this 
 structure that dendrographic bearings must be taken. The bark 
 finally becomes deeply and irregularly furrowed, so that any single 
 line around a tree may cross not more than three or four of such 
 rifts, which appear to go nearly to the wood, a condition which was 
 found in the first tree measured. 
 
 A dendrograph with a floating frame of bario in the shape of a large 
 U was mounted on a rectangular frame support and put in place on 
 No. 1 of this tree on February 17, 1919. On March 1 a slight increase 
 was recorded, but not until March 11 did positive growth begin and 
 this continued until the end of May. Temperatures (1 cm. interior to 
 the surface of the bark) of 7 to 9 C. were recorded during February 
 and March, rising to 14 C. during the growing period. Later in the 
 summer records of 18 C. were taken. 
 
 Continuous records were kept and on February 10, 1920, the instru- 
 ment was changed to one using a belt of blocks as a support for the 
 floating frame of bario. No growth of the tips of the branches had 
 yet taken place and temperatures as low as 6 C. were noted on several 
 mornings. One record of 9 C. was taken as late as March 30 in the 
 growing season. 
 
 The daily variations in this type of tree are very slight, so that the 
 record did not vary widely from a level line until March 10, when it 
 began to take an upward course which was not slackened until after 
 May 5. Growth was again actively in progress by the 18th, to slow 
 down again by the 28th, a shrinkage of marked character taking place 
 during the following week, followed by quiescence. 
 
 Growth was resumed on June 18, but soon ceased. Another impulse 
 between June 22-28, another September 25-28, were observable. A 
 decided shrinkage began on September 30, which continued for 7 days. 
 An increase took place during the last 10 days in October, and a very 
 marked shrinkage began December 1, which continued, with some
 
 32 
 
 GROWTH IN TREES. 
 
 interruptions, until about January 18, 1920. The total accretions 
 amounted to about 5 mm. in diameter, of which some was lost by the 
 shrinkage described. 1 
 
 Changes in size consequent upon rains followed until the instrument 
 was replaced on February 9, 1920, by a model using the belts of blocks 
 for a base, but retaining the U-shaped floating frame of bario. New 
 shoots 5 to 8 cm. long and leaves one-third full size were noted on 
 March 15, but no enlargement of the trunk had yet occurred. Actual 
 enlargement did not begin until April 9, one month later than in the 
 previous year. 
 
 The instrument was jammed for 2 weeks, but when set in order 
 showed continued action, justifying an estimate of the accretion not 
 recorded. Growth at a decreasing rate continued until August 1, at 
 which time a total increase of 4.6 mm. had ensued. After this time 
 the record varied but little from a level line and the instrument was 
 dismounted on September 24, 1920, the record being continuous since 
 February 24, 1919, a period of 19 months and including two entire 
 seasons. 
 
 
 ULY 
 
 II 
 
 I9Z( 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 fi- 
 
 M 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 5 
 
 n 
 
 
 
 
 
 
 
 
 
 
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 1- 
 
 ^^ 
 
 - 
 
 
 
 
 
 
 ;== 
 
 
 
 
 >- 
 
 t 
 
 fl 
 
 
 - 
 
 r^Z 
 
 
 - 
 
 
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 __- 
 
 
 MARCH 
 
 5 1920 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 __ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 FIG. 10. Dendrographic records of California live oak (Quercus agrifolid) No. 2. Beginning 
 growth, denoted by upward course of the tracing, is shown in the week beginning March 15, 1920, 
 and vigorous growth in week beginning May 31. Quiescence with small daily variations are seen 
 in week beginning July 11. Variations are X 15 on a scale of 10 mm. intervals. 
 
 The measurements of a second oak were taken for 1920 by an instru- 
 ment in w r hich the floating frame was make up of three bars of invar 
 and one bar of bario. The bark was intact and turgid, the trunk 
 having a circumference of 54 cm. at the place of measurement, 1.3 
 meters above the ground. The levers were set to amplify 16 times and 
 a thermometer was set in the bark to take temperatures of the north 
 side at about a centimeter below the surface. No growth was to be 
 seen in the tips of the branches of this tree on February 11, 1920, 
 
 1 The above statements are in part corrections of the preliminary report on this tree : The growth 
 of an oak trunk. Carnegie Inst. Wash. Year Book for 1919, see p. 77.
 
 GROWTH IN TREES. 
 
 33 
 
 although others in more exposed localities had made elongations of 
 2 to 4 cm. of the leafy shoots. A temperature of 8 C. was taken on 
 March 30, and not until April 1 was an upward movement of the pen 
 to be seen, the record for the previous 6 weeks being a level line with 
 but little daily variation. 
 
 Steady and continuous enlargement of the trunk continued until 
 June 20. After a period of quiescence, enlargement again began on 
 July 3, continuing until July 25. A total increase of 4.5 mm. in 
 diameter had taken place (fig. 10). 
 
 After a period of quiescence, with no indication of further seasonal 
 enlargement, five drain tiles, 75 cm. long, were set vertically in the 
 loose sandy soil around the tree within a radius of 2 meters from the 
 trunk, and water was turned into these openings so that 2,000 gallons 
 were taken in without overflow between 5 h 30 m p. m. of August 1 and 
 
 AUG 30 1920 
 
 AUG. 16 920 
 
 FIG. 11. Dendrographic records of California live oak No. 2 illustrated in fig. 10. A condition 
 of quiescence had been reached when irrigation was begun before 6 p. m. on August 16, with a 
 quick response in increase in diameter which continued through the week and until the middle 
 of the following week, as shown in the record in the middle of the figure. Quiescence with but 
 little daily variation is indicated in the record of the week beginning August 30. Some shrinkage 
 ensued in the week beginning September 6, 1920. Variations are X 15 on a scale with 10 mm. 
 intervals. 
 
 7 h 30 m a. m. the next morning, and 1,000 gallons were added on the 
 second night. The soil previous to irrigation had become so dry that 
 it had a moisture content of less than 6 per cent. The consequences 
 of the irrigation were extremely startling. Within 2 hours an enlarge- 
 ment was recorded by the dendrograph, which continued so that during 
 this week an actual increase of about 0.5 mm. had taken place in the 
 diameter of the trunk, including the bark. The rate soon slackened, 
 however, and no growth was visible on August 27, at which time a 
 total accretion of 1 mm. had been made to the diameter (fig. 11).
 
 34 
 
 GROWTH IN TREES. 
 
 The experiment was repeated by giving the soil around the tree 
 2,000 gallons at 9 p. m. on September 15. Again a swelling 
 was noticeable within 4 hours after the water was laid on, and not 
 more than 800 gallons had been given the soil. Enlargement con- 
 tinued for 3 days, with a total addition of 0.3 mm. to the thickness of 
 the trunk. In the ensuing quiescent period no shrinkage occurred, 
 and no swelling resulted from the rains of October 6 and 8. The 
 instrument was now dismounted. 
 
 The readiness of reaction of the live oak to increased soil-water 
 supply and the shorter period of enlargement and small relative total 
 are in contrast with the reactions of the pine grow r ing in similar soil 
 a few meters distant. The root system has been described by Cannon 
 as including a well-developed superficial portion consisting of numerous 
 short, slender roots which lie within a meter of the surface. 1 The 
 method of irrigation was calculated to wet the absorbing surfaces of 
 these roots The actual path to be traversed from the absorbing surfaces 
 
 MARCH KH7 
 
 
 
 I. fip 
 
 IB 
 
 v r, 
 
 M ! 
 
 ft. 6p.Jll2P-M.6AM. 
 
 H 6PM.12 
 
 -M.6AK M. 6PIC.12PJf.8AJl M. 6PH.12P.M6A.M. M. 6P.M. 12PM 6A.M. M. 6P.M. 12 P* 6A.M. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 ./- 
 
 - ^ 
 
 -**^_ 
 
 
 
 .. 
 
 
 
 
 
 
 2 
 
 
 
 
 
 
 
 
 "^ 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ^-*-^_ 
 
 - 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 FIQ. 12. Dendrographic record of growth and variations in Arizona ash (Fraxinut ortzontco) 
 for the week beginning March 10, 1919. Temperature of cambium region ranged from 6 to 24 C 
 A period of temperatures from 6 to 9 C. on the 15th and 16th was characterized by little, 
 shrinkage. Variations are X 10 on a scale of k !0 mm. intervals. 
 
 to the part of the trunk in which swelling was measured was not less 
 than 2 meters, and this was traversed by the water supply in such 
 quantity as to be measurable in less than 4 hours. 
 
 GROWTH OF THE ARIZONA ASH. 
 
 The Arizona ash (Fraxinus arizonica), a rapidly growing species 
 which forms a trunk 25 to 50 cm. in diameter, occurs along streamways 
 in Arizona and New Mexico. It is planted around dwellings and the 
 size attained appears to bear a direct relation to the available water 
 supply. 
 
 A dendrograph, with a floating frame of bario having two bearing 
 points opposite the lever, was attached to a tree near the residence 
 of Dr. H. W. Fenner, in Tucson, Arizona, on March 8, 1919, and a 
 thermometer was thrust under the bark. The instrument was set 
 to amplify the variations ten tunes in the record. The trunk was 
 almost exactly 1 meter in circumference and was compressed in one 
 diameter. Irrigation practice had begun for the season and the 
 
 Cannon, W. A. Tree distribution in central California. Pop. Sci. Monthly, 86:417:424. 
 Nov. 1914. See pp. 420-421 and fig. 3.
 
 GROWTH IN TREES. 
 
 35 
 
 ground was already saturated about the tree. The flower buds were 
 beginning to move, but were not so far advanced as some that were 
 seen on unirrigated land in the vicinity. The conditions were, in fact, 
 as if the plant were growing along a water-course in its natural 
 habitat (fig. 12). 
 
 Enlargement began on March 10 and continued at such rate that 
 an enlargement of 4 mm. had taken place by April 7, a period of 
 28 days (fig. 13). A period of depression and shrinkage, for 5 days 
 during a cold storm, was followed by a resumption of growth which 
 continued until August 25. Another period of depression ensued, 
 but 6 days afterwards enlargement was again noticeable which lasted 
 for a week, and other such impulses were displayed in September and 
 
 MAY 5-IZ IS 
 
 13 
 
 U.6A.M M BPJI 12pu6AJt 
 
 lit 6PM 12 
 
 .M 6. M M. 6P-M 12PJL 6A.M 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 _ 
 
 ~\ 
 
 
 
 X 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ^ 
 
 ~\ 
 
 
 
 /- 
 
 \ 
 
 
 '/ 
 
 
 ^ 
 
 
 / 
 
 
 
 
 
 
 
 
 
 
 
 
 
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 / = " 
 
 \ 
 
 
 / 
 
 
 V 
 
 / 
 
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 - 
 
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 Fio. 13. Dendrographic record of growth for the week beginning May 5, 1919, at a time when 
 the daily variations were at a maximum. Relative humidity was low and transpiration was high 
 during the midday period, at which time great shrinkage look place. Variations X 10 on a scale 
 of 10 mm. 
 
 OCT. 13-20 1919 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 
 
 
 
 
 
 v^_ 
 
 _ 
 
 
 
 *-x. 
 
 
 
 , 
 
 ^_ 
 
 X" 
 
 
 
 ^X_ 
 
 ~- 
 
 
 
 >. 
 
 - 
 
 
 
 
 
 , 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 FIQ. 14. Variations in Arizona ash during a final period of slow enlargement near the close of 
 the season, October 13 to 20, 1919. Variations X 10 on a scale of 10 mm. intervals. 
 
 October (fig. 14) ; after this equalizing variations of diminishing ampli- 
 tude only were seen until leaf -fall occurred about November 17 to 24, 
 after which the record was nearly a level line until January. 
 
 The total increase in the diameter of the tree during the season 
 amounted to about 26 mm., and a core taken from the trunk below the 
 bearings on April 20, 1921, showed a layer of 12 mm. 
 
 This instrument was replaced by a new setting on January 10, 1920, 
 with an amplification of 5 times, and the record was a continued level 
 line until April, when some equalizing daily variations began which 
 were the only changes until June 10. An enlargement now began 
 which continued until about July 20 with a depression of the rate in 
 the last week in June, which may be coupled with the high temperatures 
 and insufficient water supply of that period. Then followed only
 
 36 GROWTH IN TREES. 
 
 equalizing variations, which decreased in amplitude with the advance 
 of the season, until the record was but little away from a level line 
 until January 1921, when the instrument was dismounted to be re- 
 placed by one of improved pattern. The total increase during 1920 
 amounted to 12 mm., or about one-half that of the previous year. 
 The reduction of the measurements given was in fair agreement with 
 measurements of cores taken from the tree in February 1921. The 
 wood formed at the beginning of the season is characterized by ex- 
 tremely large vessels, which serve to denote the part of the layer formed 
 earliest in the spring. 1 
 
 Vines has described the annual rings of Fraxinus excelsior as being 
 2 to 3 mm. in thickness and as consisting of an internal spring zone 
 of wide vessels with wood-parenchyma and rather thin-walled woody 
 fibers, external to which, later in the season, thick-walled woody 
 fibers form with scattered, smaller vessels surrounded by wood paren- 
 chyma. The wood formed at the close of the season consists chiefly 
 of wood parenchyma and small, very thick-walled vessels. He notes 
 that young trees of this species in a damp soil may form a layer of 
 wood 15 mm. in thickness in a season, which is practically equivalent 
 to that of the Arizona ash under conditions of irrigation. 2 
 
 The daily variation in 1919 was greater than that seen at any other 
 time or in any other tree. Thus the daily shrinkage in March might 
 be as much as 0.4 mm., with an over-compensating increase of 0.6 mm. 
 by the following morning; in April these measurements were 1.1 mm. 
 and 1.4 mm. In May the variations rose to 1.6 and 2.1 mm. Cor- 
 related variations are displayed by elongating seedlings of the ash 
 during the same months. 
 
 The materials of which the floating frames were constructed were 
 tested to determine whether or not some of this apparent variation 
 might be due to shortening and lengthening of the metal bars and rods 
 under changing temperatures. 
 
 Calibrations of a bar of bario, such as was used in this instrument, 
 showed that its variation was 0.0000065 per unit part with 1 C. The 
 length of the axis of the yoke was 14.5 inches or 363 mm., and its 
 variation would therefore be 0.000025 mm. for 1, and 0.0005 mm. 
 for 20, which would represent the possible total in any one day. This 
 amplified 10 times by the levers would amount to about 1/200 of one 
 space on the record sheet. This would be wholly compensated by the 
 expansion and contraction of the short contact screws and by the varia- 
 tion in the instrument, so that for the purposes of this research the 
 instrumental error may be neglected. 
 
 1 The above calculations are to be used in correction of the statements in the Carnegie lust. 
 Wash. Year Book for 1919, p. 74. 
 * Vines, 8. H. Text Book of Botany, p. 198. 1895.
 
 GROWTH IN TREES. 
 
 37 
 
 GROWTH OF A BEECH TREE. 
 
 An instrument with a floating frame of bario of the U-form was 
 put in place on a beech tree (Fagus grandifolia) on the grounds of 
 Johns Hopkins University at Baltimore on April 16, 1919, about the 
 time development of the leaves was beginning. In addition to the 
 somewhat irregular daily variations swellings were seen as a conse- 
 quence of rains with subsequent shrinkage. Not until May 18, when 
 the tree was in full leafage, did some increase show in the record. 
 This continued until May 30, after which equalizing variations ensued, 
 which continued until mid-July. A week of rains was followed by 
 enlargements which continued for a month and had a net total of 
 about half that of the spring growth in May and June. 
 
 Now followed a period of regular equalizing daily variations, which 
 terminated about September 14. The ensuing enlargement, which 
 lasted for 3 weeks, showed a total increase less than hi the preceding 
 active period. Only equalizing variations were now seen and the in- 
 strument was dismounted early in October. The total accretion to 
 the diameter amounted to about 4.5 mm. (fig. 15). 
 
 EQUALIZING DAILY VARIATIONS IN DIAMETER. 
 
 The equalizing changes in the trunk are such that the diameter is 
 least at midday or in the afternoon, when the temperature of the trunk 
 is highest. The difference between the readings of a thermometer 
 thrust under the bark in early morning and at noontime is never more 
 than 8 C. or at most 10 C., while that in the center of the trunk may 
 be no more than a degree or two. Whatever the temperature might 
 be, a rise would tend to expand the woody column. Dendrographic 
 and other measurements show a decrease at this tune. The trunk is 
 seen to shrink at a time when the temperature is highest. It is obvious, 
 therefore, that we must look to causes other than a direct temperature 
 effect. 
 
 The first possibility to be tested was that of the water relations of the 
 bark, and Monterey pine No. 7 was chosen for this purpose. A small 
 section of bark and bast was removed from the north side of the tree 
 below the instrument, and these two formations were separated and 
 placed under the auxographs in the dark room in which swelling liquids 
 now stood at 12 C. The results are as below: 
 
 Constituents. 
 
 Bast. 
 
 Cork. 
 
 Water 
 
 12.5 p. ct. 
 
 p. ct. 
 
 HC1 .01 N 
 
 5 
 
 20 
 
 NaOH .01 N 
 Glvcocoll 01 M 
 
 7.5 
 10 
 
 15 
 10 
 
 
 
 
 209253
 
 38 
 
 GROWTH IN TREES. 
 
 The bast layer measured about 2 mm. in thickness throughout and 
 seemed fairly moist. The cork layer measured was light in color, pre- 
 sumably had been formed during the current season, and varied from 
 0.8 to 1 mm. in thickness. It was easily separable from the older 
 darker layers outside of it. The swelling of the bast was complete 
 in 2 hours in the acid, 4 hours in the alkali, and about 7 or 8 hours in 
 the glycocoll, while increase in water continued for nearly a day. The 
 swelling of the new cork in the acid went on at a very slow rate for 
 about 2 days, while it continued for 5 days in the alkali. It was com- 
 plete in the glycocoll solution in about 10 or 12 hours. 
 
 FIG. 16. Dendrographic records of American beech (Fopus grandifolia) , showing only slight 
 daily variations in April, increases beginning late in May and continuing until September. 
 
 Separate samples of cork and bast were taken from another place 
 on the trunk and sections were tested with the auxograph to ascertain 
 the water deficit of these tissues after a week in which growth had 
 come to a standstill, presumably on account of the dry, hot days. 
 These sections were swelled at 12 C. and the results are as below: 
 
 Solutions. 
 
 Bast. 
 
 Cork. 
 
 Water 
 HC1.01 N 
 
 7.5 p. ct. 
 10 
 
 6p.ct. 
 g 
 
 NaOH.Ol N 
 Glycocoll .01 M 
 
 22 
 15 
 
 10 
 20
 
 GROWTH IN TREES. 
 
 39 
 
 These swellings were concluded at the end of 3 days, the course of 
 enlargement being much as has been previously described. The 
 record of the variation in size of the trunk during this period showed 
 that the woody trunk made a daily variation practically equivalent to 
 that of the entire tree. 
 
 These results show that the cork in one instance was impervious to 
 water and remarkably so to the other solutions. The bast, of course, 
 takes up water readily and is easily penetrated by other solutions, 
 especially the hydroxid and amino-acid. These results may be taken 
 to indicate the possibility of some transpiration through the bark, 
 although this matter was not tested, directly. On May 22 a dendro- 
 graph was attached to a tree about 35 cm. in diameter, standing on 
 the north-facing slope north of the laboratory, for the purpose of 
 
 FIG. 16. Dendrographic record of Monterey pine No. 7, to show relative amount of variation 
 In outer and inner parts of trunk. The record for the week beginning May 24 ie for the entire 
 trunk, the bearings being taken from an inner thin layer of cork. All other records are from 
 bearings taken from the woody cylinder internal to that of 1918. The range of the daily variation 
 of the inner cylinder is seen to be less in the earlier part of the season and to decrease with the 
 season, as shown in the record for the week beginning August 30. A slight increase was seen in the 
 week beginning October 4. Variations are X 25 on a scale of 10 mm. intervals. 
 
 measuring the relative expansion of the cork and cambium layers and 
 of the wood. The plan was to attach the instrument to the tree entire 
 and to obtain the record of the daily course of change, and then strip 
 off the bark and growing layer and place the contacts of the instrument 
 on the trunk itself. The trunk was seen to be undergoing daily 
 equalizing variations with no growth in progress. Pine No. 6, a few 
 meters distant, was still showing some accretion, but with a steadily 
 lessening rate.
 
 40 GROWTH IN TREES. 
 
 After the corky bark and the softer bast had been removed, leaving 
 the woody surface bare for about 5 sq. cm. in two places, to give bearings 
 for the contact screw and lever arm, the daily equalizing variation in 
 diameter for a week had an amplitude of 0.2 mm. or one part in 1,750 
 equivalent to a change of 400 cu. cm. in volume. At the end of this 
 time the layers of wood formed in 1920 and 1918 were removed, giving 
 a new reduced diameter of 30 cm. After the bearings were adjusted 
 on these sunken surfaces, the daily variation (which at first was prac- 
 tically equivalent to that of the preceding setting of the whole trunk) 
 decreased until August, when the range of variation was about 1 in 
 8,750 parts, a range which was maintained with interruptions until 
 the close of the observations in October. The variation in the volume 
 of the wood amounted to about 80 cu. cm. (fig. 16). 
 
 In comparison with the above, it was noted that the relative range 
 of the daily equalizing variations in Pine No. 6 decreased in the same 
 ratio, both reaching an approximate minimum about September 20. 
 The behavior of the two diverged after this date. The dendrographic 
 record of the entire trunk of No. 6 shows an increase in the range of 
 daily variation, to which was added a positive increase accompanying 
 a rain on October 6, which continued until the 12th, when only the 
 equalizing variations continued, but these were of an amplitude about 
 twice that of the minimum. The woody cylinder of No. 7 ulterior to 
 the layer of 1919 also showed a swelling of the same duration as in 
 Nov 6, but the range of daily variation did not increase. 
 
 Thermometers were inserted in the trunk of No. 7 on June 1, one 
 to take the temperature of the bast and cambium region and a second 
 with its bulb at a distance of 12 cm. from the surface, which would 
 be within less than 8 cm. of the center. The course of the tempera- 
 tures during the day and with the advance of the seasons may be 
 illustrated by the following data: At 8 a. m. the outer thermometer 
 read 12 C. and the inner 13 C., at 6 p. m. the readings were identical. 
 On July 2 the outer temperature at 7 a. m. was 14 C., and the inner 
 15 C.; at 3 p. m. the readings were 17 C. and 15.5 C., and at 6 p. m. 
 identical readings of 16 C. were taken. On August 8 the outer 
 temperature was 12 C. at 7 h 30 m a. m., and the inner 13 C. At 
 l h 30 m p. m. the outer temperature had advanced to 15 C. and the 
 inner to 13.5 C. The range of temperature in the tree taken by the 
 two thermometers was 8 C. during the summer, and the difference 
 between the outer and inner readings reached its maximum of 5 C. 
 in mid-afternoon, or earlier on still hot days, equalization of the two 
 being reached shortly after sunset, with the outer portion of the tree 
 becoming cooler during the night, so that at sunrise as much of a dif- 
 ference as 1.5 C. might be seen. 
 
 The diameter, therefore, had its minimum measurement at the time 
 when the outer layers of the trunk have a maximum temperature.
 
 GROWTH IN TREES. 41 
 
 Such high temperature, with its attendant conditions of low relative 
 humidity and the local maximum of air-flow, would of course heighten 
 the rate of water loss of the entire tree. Such water loss would, of 
 course, take place from the entire surface, and although it may be 
 assumed that the rate per unit area from the trunk would be small, 
 it is yet undetermined. 
 
 Water is entering the tree through the outer membranes of the roots 
 at all times, in accordance with the balance between the soil mois- 
 ture content of the soil and the absorbing capacity of the roots. It 
 passes upward by capillarity through the vessels at a rapid rate and 
 through the system of inclosed wood-cells or tracheids at a slower rate. 
 The mass of these woody cells furnishes a structure, however, upon 
 which may be based an explanation of the shrinkage of the trunk. 
 
 Such an explanation must take into account the fact that the rate 
 of absorption by the roots shows but little daily variation, due espec- 
 ially to the fact that the temperature of the soil may vary but little 
 at the depth at which the roots lie. The rate of transpiration, how- 
 ever, which may come down to a low minimum during the night fogs 
 characteristic of the region, may rise to a high maximum during a 
 warm sunny day with a marked air-flow. The water thus lost is 
 withdrawn from the wood, either by direct outward exit through the 
 bark or upward through the branches and out through the leaves. 
 In both cases the withdrawal lessens the supply or balance in the sys- 
 tem of tracheids. 
 
 The wood of the 1919 layer, when freshly taken from the tree in 
 slips less than 2 mm. in thickness, swelled 1 per cent in water and in 
 NaOH 0.01N, while the increase was greater in HC1 0.01N, being 
 3 per cent of the original thickness. It is thus to be seen that the 
 woody tracts through which water passes upward in the tree may have 
 a water deficit of 1 part in 100 when swelled in water at a time when 
 the actual daily shrinkage amounted to but 1 in 1,700 of the entire 
 diameter. It is highly probable, however, that the deficit is unequally 
 distributed, being greater in the outermost layers. 
 
 These and other important physical problems are dealt with in 
 dendrographic measurements being carried on at the Desert Labora- 
 tory, at the Coastal Laboratory, and at other places by collaborators.
 
 8T 43
 
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