14 



HARDWOOD RECORD 



Tree Growth and the Vhysics of Wood. 



One of the interesting and important siilv 

 jects that should attract the attention of 

 himbcrmen, and esiieeially hardwood lumber- 

 men, at this period of development of this 

 great industry, is the study of tree growth 

 and the physical qualities with which woods 

 are endowed. 



The Hardwood Eecord deems it wise to 

 interrupt its series of American Forest Trees, 

 which has occupied an important place in 

 every issue since Jan. 1, 1905, to print a 

 number of articles on this subject. In this 

 connection quotations will be made from 

 leading authorities, and this information 

 supplemented by a series of spe- 

 cial articles on various divisions 

 of the general subject, by writers 

 who have given particular atten- 

 tion to the study of tree growth 

 and the physics of wood. 



It is believed that this series 

 of articles will prove timely, in- 

 teresting and instructive. Apro- 

 pos of this study, it may be wise 

 to paraphrase some of the ob- 

 servations of Herbert Stone, F. 

 L. S., who is the author of a 

 work on The Timbers of Com- 

 merce and Their Identification, 

 published by Wm. Eider & Son 

 of London. Mr. Stone says: 



It would be a difficult task to 

 answer the question why some 

 plants possess the property of 

 forming wood, while others, 

 nearly related, do not. Why 

 some plants run their course in 

 the brief period of a year, and 

 perish as soon as they have 

 given birth to another genera- 

 tion, while others persist and 

 augment their bulk year by year 

 for centuries. There is nuu-h 

 food for reflection here. 



Such plants as are endowed 

 with the faculty of secreting a 

 substance which resists decom- 

 position for a long time, and of 

 fortifying their tissues with it, 

 play a verj' different part in the 

 world's economy to that of their 

 herbaceous relatives, which today 

 are, and tomorrow are cast into 

 the oven. They exist long enough ' 



to acquire an individual history. This history 

 may not be written in human records, but it 

 has a record of another kind, which may be 

 read in the structure of the tree itself, which, 

 like the nautilus, adds a chamber to its 

 habitation every year by surrounding itself 

 with a fresh layer of wood. 



These layers are perhaps the most familiar 

 feature with which all those who have used 

 timber, or have noted the cut ends of fallen 

 trees, are acquainted, but it occurs to few 

 that the innermost tiny ring enclosing the 

 pith is the section of a stick that was once 

 the seedling tree. The seedling is a small 

 object, a few inches high at most, and the 

 layers which have been added year by year, 

 were it possible to separate them, woulcl ap- 

 pear as long taper tubes of wood. 



The annual addition to a tree's growth is, 

 in fact, a conical sheath tapering to a point, 

 and capable of accommodating the plant 



within to its topmost bud. A seedling is 

 two years old, but not as a child, who is two 

 years old to his innermost parts, for the 

 tree is only one year old as regards its outer 

 portion. The two layers are not merged in 

 one another ; the second is merely added. In 

 the case of a full-grown oak, a century old, 

 only the pith and first coat of wood bear 

 that age; the next coat is only ninety-nine 

 years old, and the outermost but one. More- 

 over the topmost branches are quite young, 

 and their • innermost parts, scores of feet 

 above the tip of the little seedling from 

 which they Imve grown, are scores of years 

 younger, even to their pith. Of an ancient 

 hollow tree it may be said that perhaps 

 Kobiii Tlood (lined benrath its brandies. The 



WAYS IN WHICH WOOD MAY BE Ct'T : A. CROSS SECTION 

 11. I!A r>IAL SECTION ; C, TANGENTIAL SECTION. 



general impression is correct, but the fact 

 is not precise ; for the tree is no older than 

 its component parts, which, being entirely 

 outcrparts, are. merely the growth of the 

 last fifty years or so, as a section of the 

 wood will jirove. 



A tree, then, is a living organism whose 

 component parts are of various ages; and 

 upon it arise successive generations of leaves, 

 much as a city rears its people or a coral 

 reef its polyps. The living portion is re- 

 newed from time to time, adds something to 

 the tree, and passes away. Time too brings 



all trees, for some exhibit no distinction in 

 this respect and are the so-called sap-wood 

 trees, though even here changes take place 

 which bring the timber to maturity. In a 

 living heart-wood tree there can be dis- 

 tinguished the pith, heart-wood, sap-wood, the 

 iictive living layer or cambium, the bast and 

 tlie bark. The cambium layer is a very deli- 

 cate sheath of thin tissue which is the source 

 of the new wood, and which by the multipli- 

 cation of its elements or cells adds layer 

 upon layer to the wood already formed. Ou 

 its outer side it adds to the bast, but in a 

 much smaller degree. 



The bark, enclosing all in an impervious 

 clothing, serves the purpose of checking the 

 evaporation which . would endanger the exist- 

 ence of the delicate cambium 

 layer within. 



The young wood lying nearest 

 tlie outside jiartakes of the na- 

 ture of the cambium at first, but 

 lapidly becomes altered. The 

 walls of its cells, originally thin, 

 l)ecome thickened and woody, but 

 for some time they retain their 

 ■ apacity for absorbing water, 

 and form the channel by which 

 the water from the roots ascends 

 to the leaves. The further from 

 the bark, the less is this capacity 

 possessed by the wood, and 

 though it is rarely if ever quite 

 lost, yet the difference in the 

 rate of absorption of water by 

 the sap-wood and heart-wood is 

 considerable, as can be seen by 

 moistening the cut surface of a 

 piece of w-ood where both art 

 present. While the water sinks 

 rapidly into the sap-wood it sen- 

 sibly lingers on the surface of 

 the riper part. The vital pro- 

 cesses which constitute the phys- 

 iology of plant life are beyond 

 the scope of this work, which 

 deals solely with their product — 

 the wood, which while living is a 

 tree, but being dead is timber. 



As, then, a tree consists of 

 i-oncentric cones of wood, if it is 

 sawn into planks the outermost 

 plank will be a curved flitch of 

 bark, with some sap-wood on its 

 inner side. The next plank will 

 liave sap-wood down the edge, 

 ;ind a strip of heart-wood down 

 the middle, which strip will in- 

 crease in width, plank by plank, 

 until the center of the tree is 

 reached. Lines which mark oif 

 cone from cone (that is, annual ring from an- 

 nual ring) may be seen parallel at the lower 

 end, but will join as loops at the upper. 

 It is only when the section approaches the 

 horizontal that the annual rings approach 

 the circular, so that oblique cuts show an 

 almost infinite variety of form. In fact, 

 two planks are never alike in every detail 

 of figure except by accident. 



I have referred to the Autumn and Spring 

 zones as though all woods possessed them, 

 and it will be found that the same ex- 

 pressions are generally employed in the 

 literature of forestry. They are of course 



other changes due to other causes than the 



nourLshment afforded by the yearly labor cnly appropriate in connection with those 



of the leaves, and as year by year a new species which grow in temperate climates. 



coat of wood is added, so does an inner 

 layer lose its vitality and become inert, and 

 so does a still deeper layer undergo still 

 further changes which produce the heart- 

 wood. This heart-wood will not be found in 



as the period of greatest vigour in tropical 

 trees is not necessarily that of Spring, while 

 it is possible that there is no resting period 

 like our Winter. Judging from the structure 

 this state of things is by no means unusual, 



