iONOMIC OF;;T UNITED STA^fj» SAMUEL J. RE m % ■§. JL pill pbrarg ^fortlj Carolina jltaic College 5H455 "R5 #» NORTH CAROLINA STATE UNIVERSITY LIBRARIES S01 948772 Date Due JMarS'gg iMprl'33 an!934 fab34 !5Feb34 I)lar34 ■of |E! rffc ?c t4May'51 ■27Feb»B , "t|0V 7 ■ee+ "TON" JftW 6 MAR lb 4862- 196fr TI964" w l?IUr34 7W51'v lpiF5 4 APR ^r-t9SB 5Feb3 9 i9Feb35 29Apr'58r JUN , 20 ■ ••- ABM 5 Mar3S ^AN 1 I 1 967 i¥Mar3d 2 , w6 k j!6May3jr "7^- ~~ — ST**' NOV 7 1962 — _ "i i' ^°0^ Hi Quercus alba (white oak) : cross section through one entire growth ring and portions of two others. Note large pores in early wood filled with tyloses and abruptly diminishing in size toward late wood. Small pores thin-walled and in lan-like groups. Note "dipping in" of the outline of the growth ring where it crosses the large ray at the right X 35. Identification OF THE Economic Woods of the United States Including a discussion of the Structural and Physical Properties of Wood BY Samuel J. Record, M.A., M.F. Professor of Forest Products, Yale University SECOND EDITION REVISED AND ENLARGED NEW YORK JOHN WILEY & SONS, Inc. London : CHAPMAN & HALL, Limited 1919 BY THE SAME AUTHOR Mechanical Properties of Wood. viii -f- 167 pages, 6X9, 51 figures, 22 tables Cloth, $2.50net. Copyright, 1912, 1919 By Samuel J. Record Stanbope jpress GILSON COMPANY BOSTON, U.S.A. CONTENTS PAGE Introduction 1 PART I Structural and Physical Properties of Wood: General 5 Pith 7 Bark 8 Primary wood .11 Cambium 12 Secondary wood 12 Vessels 14 Tracheids 16 Wood fibres 18 Wood parenchyma 21 Rays 23 Resin ducts 29 Pits 31 Tyloses 35 Pith flecks or medullary spots ....... 36 Trabecular: Sanio's beams . 38 " Ripple marks " 39 Growth rings 40 Heartwood and sapwood 44 Grain and texture 46 Knots 48 Density and weight 49 Water content of wood 52 IV CONTENTS PAGE Shrinkage, warping, and checking 56 Hygroscopicity 59 Permeability 60 Conductivity 62 Resonance ........... 62 Color 64 Gloss or lustre 66 Scent or odor 67 Taste 69 Additional References 69 PART II Key to the Economic Woods of the United States . . .73 References 109 Bibliography 119 Appendix 127 Index .,..'.......... 147 ILLUSTRATIONS PLATE Cross section of Quercus alba (white oak) .... Frontispiece PLATES Map of the United States showing natural forest regions . . I Photomicrographs of wood sections ....... II-VI TEXT ILLUSTRATIONS Fig. page 1. Cross sections of stem of Quercus prinus (chestnut oak) ... 6 2. Typical wood cells 19 3. Radial sections of heterogeneous rays ...... 24 4. Radial section of ray of Pinus strobus (white pine) . . . .25 5. Radial section of ray of Pinus edulis (pinon pine) . . . .26 6. Radial section of ray of Pinus resinosa (red pine) . . . .27 7. Radial section of ray of Pinus palustris (longleaf pine) . . .28 8. Cross section through portions of two growth rings of Pinus ponderosa (western yellow pine) ........ 30 9. Tangential section of fusiform ray of Pinus ponderosa (western yellow pine) 31 10. Cross section of a wound area of Tsuga canadensis (eastern hemlock) 32 11. Schematic representation of pits 33 12. Bars of Sanio in Pinus murrayana (lodgepole pine) . . . .38 13. Cross section through three entire growth rings of Quercus macrocarpa (bur oak) 42 14. Cross section through one entire growth ring and parts of two others of Quercus macrocarpa (bur oak) . . . . . .42 15. Effects of shrinkage 57 TABLES NO. PAGE I. Length of tracheids in coniferous woods 17 II. Length of wood fibres in dicotyledonous woods . . . .20 III. One hundred and fifty trees of the United States arranged in the order of the average specific gravity of their dry woods . 50 IV. Shrinkage of wood along different dimensions . . . .57 V. Important families and genera of Dicotyledons in the United States 129 VI. Numerical conspectus of the trees of the United States . .129 VII. Indigenous woods with vessel perforations exclusively or predomi- nantly simple 135 VIII. Indigenous woods with vessel perforations exclusively scalariform 136 IX. Indigenous woods with spiral markings in part or all of the vessels 138 X. Nature of pitting of vessel wall where in contact with ray paren- chyma . . . . . 139 XI. Occurrence of tyloses and gum deposits in vessels of indigenous woods 141 XII. Families with indigenous representatives exclusively diffuse-porous 143 XIII. Indigenous ring-porous woods 143 XIV. Nature of pitting in wood fibres of indigenous woods . . .144 XV. Kinds of rays in indigenous dicotyledonous woods . . .145 XVI. Indigenous woods with " ripple marks." ..... 146 PREFACE TO THE SECOND EDITION The chief differences between this edition and the first (1912) are as follows: (1) The Key has been entirely rewritten and re- arranged, several new woods are included and more of the common names are given; (2) the lists of references and the general bibli- ography have been brought up to date; (3) an Appendix has been added which amplifies some of the subject matter of Part I, and also includes considerable new data on wood structure. In grouping the woods in the Key more attention has been given to their general similarity than to special features, thus bringing together for effective contrast the kinds which are most likely to be confused in practice. Attempt has been made to have all of the descriptions comparable and, so far as permissible, to make the gross characters the basis for separation. The micro- scopic features are "printed in smaller type than the others, to avoid confusion and to simplify the use of the Key. It is comparatively easy to make a key for a given lot of wood specimens, but to take into account the range of variation of each wood is an extremely difficult task. Such a key must be the re- sult of growth, of the accumulation of years of investigation and experience, and must always be subject to revision as new data and new material become available. To this end the author would enlist the cooperation of all readers of this book. Samuel J. Record. INTRODUCTION As the available supply of the standard kinds of timber has decreased, woods have appeared on the market which formerly were considered worthless. In some instances the new woods are sold under their own names, but usually they are employed as substitutes for more expensive kinds, or sold in indiscriminate mixture. It thus becomes a matter of great importance that foresters, timber-inspectors, and wood-users be able to distinguish the woods with which they deal. The number of such woods is so large, and their resemblance often so close, that one can no longer depend upon distinguishing them through mere familiarity with their general appearance. To identify woods it is necessary to have a knowledge of the fundamental differences in their structure upon which the points of distinction are based. The literature bearing directly upon this subject is very limited, and such information as exists is for the most part dis- tributed throughout a considerable number of publications and not readily available. Teachers and students of wood technology are seriously handicapped by the lack of suitable text-books or manuals. It is in an attempt to supply in small part this defi- ciency that the writer has prepared for publication a portion of the material given in one of his courses in Forest Products at the Yale Forest School. While it is designed primarily as a manual for forestry students, it is hoped that it will also aid others in the study and identification of wood. Part I deals briefly with the more important structural and physical properties of wood. The structural properties are based upon the character and arrangement of the wood elements. Under this head are considered: (a) the external form of the tree in its various parts; (b) the anatomy of the wood; (c) abnormal developments or formations; (d) relation of these properties to the usefulness of wood; and (e) their importance in classification. The physical properties are based upon the molecular composition of the wood elements. Under this head attention is given to (a) the properties manifest to unaided senses, viz., color, gloss. 1 2 INTRODUCTION odor, taste, and resonance; (b) those determined by measurement,. viz., density, weight, water content, shrinkage, swelling, warping, and hygroscopicity ; (c) relation of these properties to the use- fulness of wood; and (d) their employment to some extent as aids, to identification. In Part II attempt is made to use the details of Part I in the construction of an artificial classification of the economic woods of the United States. Unimportant species have in some cases- been included where it was felt that their presence would not lead to confusion. This classification has been prepared with two objects in view: (1) for use in practice as a key for the identifica- tion of unknown specimens ; (2) for use in the laboratory as a basis for the comparative study of known specimens. As far as considered practicable, the distinctions in the key are based on macroscopic features, those readily visible to the unaided eye or with the aid of a simple lens magnifying 10 to 15 times. Owing to the great variation of wood it is usually unwise to rely upon single diagnostic features, and for this reason the descriptions have been extended to embrace all or most of the important characters so far recognized. This method also permits ready arrangement of the key or the fitting into it of additional woods. In the woods of many genera the structural variations appar- ently are not sufficiently distinct and constant to assure specific identification. Good examples of this are afforded by the woods of Pinus, Quercus, Hicoria, and Populus, where it is usually difficult and very often impossible to do more than separate them into groups. Accurate knowledge of the botanical and com- mercial range of each species will often serve as a basis for further subdivision of a group in which other distinctions are apparently wanting. In preparing a specimen for careful examination either with or without a lens it is highly desirable that a very smoothly cut surface be obtained. If the knife used is not sharp, the cut surface will be rough and the details of structure obscured. Cross sections are, as a rule, the most valuable for comparative study, and in making them it is very important that the plane of section be as nearly as possible at right angles to the vertical axis of the specimen. A compound microscope is necessary for the study of the minute anatomy of wood. Sections for immediate observation INTRODUCTION 3 may be cut free-hand with a sharp pocket-knife or razor and mounted in water. To avoid air bubbles in the sections small pieces of the specimens should be boiled prior to sectioning. It is not important that such sections be of uniform thickness, since a thin edge will usually exhibit the essential details- Much better results can be obtained by the use of a microtome. Penhallow recommends a table microtome and a plane blade mounted in a heavy wooden handle of such a form as to provide a perfectly firm grip. For fine work, however, a sliding microtome specially constructed for sectioning wood is best. Success depends largely upon the sharpness of the knife and the rigidity of the apparatus. Considerable care should be exercised in the selection of material for sectioning. Small blocks of about a quarter-inch cube should be cut from green material, or from the interior of dry pieces. The faces of the blocks should represent sections which are as nearly cross, radial, and tangential as possible. Blocks of the lighter woods can be softened sufficiently by boiling them in water until thoroughly saturated. The process may be hastened by interrupting the boiling by additions of cold water. In the case of the harder woods, however, it is a good plan to place the small blocks, after boiling, in a solution of hydrofluoric acid for a period varying from ten days to three weeks, the strength of solution and the duration of immersion depending upon the hardness of the wood. After removal from the acid the blocks should be thoroughly washed and then placed for several days in glycerine, after which they are ready for sectioning. The sections may either be mounted unstained in glycerine or stained in the usual way and mounted in balsam. For ordinary work unstained glycerine-mounts afford the most satisfactory results, since the natural colors are preserved. (For more detail, see references below.) References Bailey, I. W.: Microtechnique for Woody Structures, Bot. Gaz., Vol. XLIX, Jan. 1910, pp. 57-58. Plowman, A. B.: The Celloiden Method with Hard Tissues, Bot. Gaz., Vol. XXXVII, June 1904, pp. 456-461. Penhallow, D. P. : North American Gymnosperms, Boston, 1907, pp. 16-23. Benedict, H. M.: An Imbedding Medium for Brittle or Woody Tissues, Bot. Gaz., Vol. LII, Sept. 1911, p. 232. Thompson, R. B.: A Modification of a Jung-Thoma Sliding Microtome for Cutting Wood, Bot. Gaz., Vol. L, Aug. 1910, pp. 148-149. 4 INTRODUCTION The best idea of the form and size of the individual cells is gained from study ing macerated material. This is readily obtained by placing small pieces of wood in a test-tube together with a number of crystals of potassium chlorate, and adding enough nitric acid to cover them well. After the wood has turned white the solution should then be poured off and the material washed thoroughly in water. This action may be hastened by warming. It is then easy to remove a small portion of the mass to a slide where it can be dissected with a couple of needles and studied under the microscope. The writer desires to acknowledge his indebtedness to Prof. James W. Tourney for much of the da.ta upon which this work is based; to Mr. Clayton D. Mell for many helpful suggestions and criticisms; and to Mr. Charles J. Heller for the loan of a set of wood sections from which the photo-micrographs were made by the writer at the Forest Products Laboratory, Madison, Wis- PART I STRUCTURAL AND PHYSICAL PROPERTIES OF WOOD Wood of a timber-producing tree may be considered under three general heads, viz., root, stem, and branch. The relative proportion of the three classes of wood in a tree depends on the species, the age, and the environmental conditions of growth. The woody portion of stem and branch has, within certain limits, the same structure. Branches are of less technical value because of their irregular shape and small dimensions. The latter is due to the fact that the number and thickness of the layers of growth are less and the wood elements smaller than in the bole. Wood of roots always differs somewhat from that of the stem in form, structure, and distribution of the elements; the growth rings are narrower, the elements have wider lumina, and the wood is as a rule lighter, softer, and more porous. Roots, with occasional exceptions, are a very subordinate source of wood in America. Stem wood, on account of its more desirable dimensions and shape and its greater uniformity, is of the greatest utility and value. The form and character of the stem are of greater impor- tance than the relative volume; with few exceptions the more nearly straight and cylindrical and the freer from limbs, knots, and defects, the greater are its technical properties and value. These properties are largely determined by the age of the tree and the inherent characteristics of the species, though affected by environment. Straightness and clearness are materially influenced by density of stand. A woody stem, branch, or root is composed of three unlike parts (Fig. 1). Through the central portion runs a narrow cylinder of soft tissue, the pith. On the outside is bark. Between these two and making up the bulk of the structure is the wood or xylem. The wood, particularly in old sections, usually shows a central 5 6 ECONOMIC WOODS OF THE UNITED STATES colored portion, the heartwood, and a nearly colorless outer border, the sapwood. In fresh-cut green sections the sapwood is further differentiated by its greater moisture content. Indigenous arborescent plants are readily separable in o two Fig. 1. — Cross section of stem of Quercus prinus (chestnut oak); b, bark showing outer and inner portions; s. w., sapwood; the darker inner portion is heartwood; a. r., annual or growth ring; p. r., (pith) ray, a large number of which can be seen crossing the growth rings at right angles. Note season checks. Natural size. (From Bui. 102, U. S. Forest Service.) great natural classes: I, Gymnosperms, and II, Angiosperms. Class I is further divided into two unequal groups: Coniferce (13 genera), and Taxacece (2 genera). Class II embraces (according to ECONOMIC WOODS OF THE UNITED STATES 7 Sargent's " Manual of the Trees of North America"), Mono- cotyledons (2 families and 8 genera), and Dicotyledons (62 fam- ilies and 162 genera) . The Monocotyledons are of comparatively slight importance as sources of wood, and for that reason, as well as on account of their peculiar structure,* are omitted from the general discussion of wood and from the key. The woods of the Gymnosperms are commonly referred to as ''coniferous woods," "softwoods," and " needle-leaved woods." These terms are inexact since (1) the Taxacece do not bear cones; (2) many of the so-called "softwoods" (e.g., Pinus palustris, Pseudotsuga, Taxus) are harder than many of the so-called "hard woods" {e.g., Populus, Salix, JEsculus, Tilia); and (3) the con- trast in the leaves is by no means always as great as the terms "needle" and "broad" would indicate. Common usage, how- ever, has given these names sufficient definiteness for ordinary purposes, though they should be avoided where scientific exact- ness is desired. PITH The central portion of the young shoot, branch, and root is composed of loosely aggregated, mostly thin-walled, isodiametric, parenchymatous cells — the pith. It is usually of small diameter, does not increase in size after the first year, in fact, may even in some instances be compressed, and appears to be of only temporary utility to the tree. In some cases, according to Gris (loc. tit.), the cells remain active for several years, and alternately store and give up products of assimilation, especially starch and tannin, according to the periods of vegetation. In such instances the walls of the active cells are thickened and densely pitted. The pith in woody stems of Gymnosperms is fairly uniform in shape, size, color, and structure; in Dicotyledons there is great variation. As to outline in cross section: it is star-shaped in Quercus, triangular in Fagus, Betula, and Alnus; ovoid in Tilia, Fraxinus, and Acer; circular in Juglans, Ulmus, and Cornus. In Juglans the color is black; in Gymnocladus it is red; in many others it is brown or gray. In Rhus, Sambucus, and Ailanthus the * In adult steins of Monocotyledons the fibro-vascular bundles are scat- tered throughout the central cylinder instead of being disposed in a circle, as in the Dicotyledons. The bundles are closed and the tracheary tissue surrounds the phloem. 8 ECONOMIC WOODS OF THE UNITED STATES pith is comparatively large and conspicuous, often deeply colored. In Magnolia, Liriodendron, Nyssa, Asimina, and Anona there is often a more or less distinct septation of the continuous pith by plates of stone cells, while in Juglans there is decided septation but the diaphragms are not sclerotic, and the pith is not con- tinuous between the disks. On account of these and other pecu- liarities the pith when present in a specimen of wood is frequently an aid to identification. References DeBary, A.: Comparative Anatomy, Oxford, 1884, pp. 402-403; 533-534. Foxworthy, J. W.: Discoid Pith in Woody Plants, Proc. Indiana Academy of Science for 1903, Indianapolis, 1904, pp. 191-194. Solereder, Hans: Systematic Anatomy of the Dicotyledons, Oxford, 1908, pp. 133-134. Gris, A.: Sur la Moelle des Plantes Ligneuses, Amer. Sci. Nat., Ser. 5, Tome XIV, 1872. Bark is the name commonly applied to that portion of a stem lying outside the cambium layer. Used in this broad sense, it is customary to distinguish an outer (dry) portion and an inner (living) portion. The structure of bark is highly complex and widely variable. When shoots are first formed they are covered by a very thin layer of tissue, the epidermis. Beneath this is the primary cortex and the pericycle. The latter is commonly composed of two kinds of tissues, thin-walled parenchyma and bast-fibres. The bast- fibres may occur in isolated groups or form a continuous band around the stem. When in groups they are often closely associated with, but not really part of, the phloem of the vascular bundles. Bast-fibres are attenuated sclerenchymatous elements, with sharp ends simple or branched. Their function is to give strength to the stem and to protect the delicate tissues of the phloem. It is to them that many barks owe their great tough- ness and pliability. Phloem, which is the outer portion of a vascular bundle, is in typical cases composed of sieve tubes, companion cells, and phloem parenchyma. In structure sieve tubes resemble vessels, but their walls are mostly delicate, non-lignified, colorless, cellulose mem- ECONOMIC WOODS OF THE UNITED STATES 9 branes. Between the ends of the sieve-tube segments (and some- times between adjacent side walls as well) are thin plates dotted with pits, resembling a sieve. The pit membranes are finally absorbed, allowing free communication from one cell to another. Unlike vessels, the segments of the sieve tubes remain alive for a year or more, though they lose their nuclei. This unusual phe- nomenon may be due to some influence of the companion-cells or to associated parenchyma cells. The function of the sieve tubes is the vertical (especially downward) distribution of elab- orated food materials. After the first year the cells usually be- come crushed by the pressure of the surrounding tissues, their places being taken by new cells generated by the cambium. In addition to the structure just mentioned, many other elements and structures may enter the composition of the bark. Among these may be mentioned resin ducts, latex tubes, stone cells, crystals, mucilage sacs, and tannin sacs. Bast rays are also present, being continuous with the rays of the xylem. They increase in width uniformly and gradually as they recede from the cambium. In practically all cases of growth in thickness the epidermis is destroyed at an early period and is replaced by cork. Cork is suberised tissue formed by a special meristem called cork cambium or phellogen, which originates in the epidermis or in the cells just beneath the epidermis. All parenchymatous cells, however, wherever located, appear to possess the ability to form cork. Wound surfaces are closed and healed by it, and diseased and dead parts are isolated from those in living condition. The formation of cork cambium in the bark usually occurs during the first year's growth of the stem. As a result of its activity a layer of cork cells is generated on the outside, and fre- quently a layer of thin-walled parenchyma cells — the phelloderm — on the inside. Collectively these new tissues, including the cork cambium, are called the periderm. The effect of the development of cork is to cut off from the interior mass of tissue portions of the cortex, which dry up and are eventually thrown off as outer bark. This action may occur only once, as in Fagus and Carpinus, but usually is repeated, and successively deeper layers of the cortex and eventually of the pericycle and phloem are cut off. In some species the successive formations of cork extend more or less uniformly around the stem, cutting off in each case an annular layer of cortex — sometimes called ring bark. In other species the successive internal layers are very irregular, and cut 10 ECONOMIC WOODS OF THE UNITED STATES off scale-like portions of the cortex — scale-bark. The results are subject to very wide variation. In Platanus and Taxus the outer bark is shed annually in the form of comparatively large, irregular, thin flakes which, falling away, leave the surface smooth. In species of Betula thin, exfoli- ating layers are produced, marked with horizontal lines of lenticels. In many species of Pinus, the outer bark of mature trees is made up of small, irregular scales in very intricate pattern. In Hicoria ovata and H . laciniosa the outer bark peels off in long, flat, reddish- brown strips, while several other species of the same genus have bark that is not flaky. In a great many woody plants the layers of bark persist for many years, and, as the stem increases in size, become more and more cracked and furrowed. Such is the case in Quercus, Robinia, Liriodendron, etc. In Sequoia, Juniperus, Taxodium, and others of the Cedar group, the bark is character- istically fibrous. These examples are sufficient to indicate the wide variation in the bark and its importance as an aid to the identi- fication of a specimen upon which any portion of bark remains. The bark of many trees is of high technical value. A very great number are used for medicinal purposes. Tsuga and species of Quercus possess barks which contribute very largely to our tannin supply, upon which the leather industry is dependent. Some barks contain coloring principles; others (e.g., Hicoria ovata) are highly valuable for fuel. Birch bark was formerly used for canoes. The inner barks of some woods (e.g., Tilia) are sometimes used in manufacturing fibre cloth. The highly-developed corky layers of Quercus suber furnish the cork of commerce. References Stevens, W. C: Plant Anatomy, Philadelphia, 1907, pp. 37-39; 56-58; 72-82. DeBary, A.: Comparative Anatomy, pp. 108-114; 519-566. Sachs, Julius: Text-Book of Botany, Oxford, 1875, pp. 90-92. Gregory, E. L.: Elements of Plant Anatomy, Boston, 1895, pp. 133-142. Henkel, Alice: American Medicinal Barks, Bui. 139, U. S. Bu. Plant Industry, 1909, p. 59. Hill, Arthur W. : Sieve-Tubes of Gymnosperms, Annals of Botany, Vol. XV, Dec. 1901. : Notes on the Histology of the Sieve-tubes of Certain Angiosperms, Annals of Botany, Vol. XVII, Jan. 1903, pp. 265-267. Moeller, Joseph: Anatomie der Baumrinden; Vergleichende Studien, Ber- lin, 1882, p. 447. ECONOMIC WOODS OF THE UNITED STATES 11 PRIMARY WOOD At the growing apex of a stem is an undifferentiated tissue composed of very thin-walled cells essentially all alike. This tissue is known as the 'primordial meristem. Below the apex the primordial meristem becomes differentiated into three distinct parts, viz., (1) the protoderm at the outside, (2) the procambium strands, and (3) the fundamental or ground meristem. These three regions or tissues are themselves subject to further differentiation and are called primary meristems. The protoderm changes into the epidermis; the ground meristem into pith, primary rays, pericycle, and primary cortex; the pro- cambium strands into vascular bundles, which are disposed in a circle around the pith and separated from each other by the primary rays. The vascular bundles are composed of three parts, an inner called the xylem, an outer called the phloem, and, separ- ating the two, a thin layer of generative tissue, the cambium. These tissues, being the direct development of the cells of the procambium, are termed primary (primary wood — proto- xylem and metaxylem — and primary phloem), in contradistinction to the tissues generated by the cambium, which are termed secondary. Primary wood is relatively unimportant, though of scientific interest because of its peculiar structure, which in many ways differs from the other wood of the stem. Thus in Angiosperms, wood fibres are usually wanting and tracheids are not common in the primary wood, while in the secondary wood fibres are always present and tracheids commonly so. In Gymnosperms the vascular elements of the primary wood are indeterminate in length, marked with spirals and for the most part devoid of pits in their walls, while the corresponding elements in the secondary wood are of determinate length, rarely marked with spirals and always pitted. References Stevens, William C: Plant Anatomy, pp. 25-45. Penhallow, D. P. : North American Gymnosperms, pp. 38, 40. DeBary, A.: Comparative Anatomy, p. 321. Sachs, J.: Text-Book of Botany, p. 574. 12 ECONOMIC WOODS OF THE UNITED STATES CAMBIUM As previously stated, that portion of a pro-cambium strand which remains capable of division and generation is known as fascicular (i.e., bundle) cambium, since it produces on the inner side wood or xylem, and on the outer phloem — collectively a fibro- vascular bundle. The cambia of the several bundles are later united into a continuous sheath, and the portion between the original bundles is termed the inter-fascicular cambium. The cambial layer sheathes the entire woody cylinder from root to branch and separates it from the cortex or bark. It is composed of a thin layer of delicate, thin-walled, vertically elongated cells filled with protoplasm and plant food. It is this layer that is torn when bark is stripped from a living tree. During vigorous growth, "when the sap is up," the cells of the cambium are par- ticularly delicate, a fact taken advantage of in peeling poles, logs, and basket-willow rods. The division and development of the cambial cells give rise to (a) a layer of new wood on the outside of that last produced; (6) a layer of new phloem on the inside of that last produced ; (c) continuation of the medullary rays of both xylem and phloem; and (d) new cambium. / References DeBary, A.: Comparative Anatomy, pp. 454-475. Bailey, I. W.: Relation of Leaf -Trace to Compound Rays in Lower Dicoty- ledons, Annals of Botany, Vol. XXV, No. 97, June 1911. Rubner, Konrad: Das Hungern des Cambiums und das Aussetzen der Jahfringe, Naturw. Zeitschrift fur Forst- und Landwirtschaft, 8. Jahr- gang, 1910, pp. 212-262. Von Mohl, Hugo: Ueber die Cambiumschicht des Stammes der Phanero- gamen und ihr Verhaltniss zum Dickenwachsthum desselben, Bot. Zeitung, Vol. XVI, 1858, pp. 183-198. SECONDARY WOOD Tissues formed from cambium are termed secondary. Almost all of the wood of a stem is secondary wood, the small amount of primary wood being wholly negligible from a technological point of ^iew. The principal functions of secondary wood are (a) to provide ECONOMIC WOODS OF THE UNITED STATES 13 mechanical support for the tree; (6) to afford means for the ascent of sap from the roots to the foliage; (c) alternately to store up and to give back products of assimilation, particularly starch. While the elements of secondary wood are subject to wide variation, they may for convenience be referred to three principal types, viz., (1) vascular, (2) fibrous, (3) parenchymatous. Between these groups are transitional and specialized forms whose reference to one or the other of these groups is often purely arbitrary. The classification may be extended as follows: Vascular elements True vessels Tracheids (wood) tracheids ray tracheids Fibrous elements Wood fibres Septate wood fibres Parenchymatous elements Wood parenchyma Ray parenchyma In the following table are shown side by side the important differences in the distribution of the elements in typical secondary wood of Gymnosperms and Dicotyledons. (See Appendix, p. 131.) Gymnosperms True vessels absent. Wood tracheids present and forming bulk of wood. Ray tracheids present or absent. Wood fibres absent. Wood parenchyma present (except in Taxacece), but usually subordinate. Ray parenchyma present. Dicotyledons True vessels present. Tracheids present or absent; always subordinate. Ray tracheids absent. Wood fibres present. Wood parenchyma present, and very often conspicuous. Ray parenchyma present. From the above it is apparent that the wood of Dicotyledons is more heterogeneous in its nature than that of Gymnosperms, which is composed almost wholly of tracheids and ray parenchyma. References Solereder, H.: Anatomy of the Dicotyledons, Vol. II, pp. 1133-1168. DeBary, A.: Comparative Anatomy, pp. 458-500. Boulger, G. S.: Wood, London, 1908, pp. 1-54. Stevens, W. C: Plant Anatomy, pp. 48-56; 72-112. Sachs, J.: Text-Book of Botany, pp. 92-102. Mell, CD.: A Confusion of Technical Terms in the Study of Wood Struc- ture, For. Quarterly, Vol. IX, No. 4, 1911, pp. 574-576. : Classification of Woods by Structural Characters, Am. Forestry, Vol. XIV, April 1910, pp. 241-243. 14 ECONOMIC WOODS OF THE UNITED STATES Stone, H. : The Use of Anatomical Characters in the Identification of Wood, 'Nature, Vol. LXV, No. 1686, 1902, pp. 379-380. Gayer, K.: Schlich's Manual of Forestry, Vol. V, 1908, pp. 7-19. Metzger, K.: Ueber der Konstructionsprinzip des secundaren Holzkorpers, Naturw. Zeitschrift fur Forst- und Landwirtschaft, 6. Jahrgang, 1908, pp. 249-273. Wieler, A. : Ueber die Beziehung zwischen Wurzel- und Staumholz, Forstw. Jahrbuch, Tharand, Vol. XLI, 1891, pp. 143-171. Hartig, Robert: Untersuchungen iiber die Entstehung und die Eigenschaf- ten des Eichenholzes, Forstlich-naturw. Zeitschrift, Vol. Ill, 1894, pp. 1-13; 49-68; 172-191; 193-203. Hartig, Robert, and Weber, Rudolph: Das Holz der Rothbuche in Ana- tomisch-physiologischer, Chemischer und Forstlicher Richtung, Berlin, 1888, pp. 20-28. Sanio, Carl: Vergleichende Untersuchungen uber die Elementarorgane des Holzkorpers, Botanische Zeitung, Vol. XXI, 1863, pp. 85-128. : Verg. Unt. u. d. Zusammensetzung des Holzkorpers, Ibid., Vol. XXI, 1863, pp. 358-412. Wiesner, Julius: Die Rohstoffe des Pflanzen Reiches, Vol. II, Leipzig, 1903, pp. 1-35. vessels (see Appendix, p. 132) Vessels are indeterminate, tube-like cell-fusions found in the wood of all indigenous dicotyledonous plants. In fact the absence of xylem vessels in woody Dicotyledons is a very rare phenomenon which, according to Solereder (loc. cit., p. 1136), has been recorded only in the exotic genera Drimys and Zygogynum of the Mag- noliacece, and Tetracentron and Trochodendron of the Trochoden- dracece. Vessels arise from cambial cells which increase in size and, through the partial or complete absorption of their end-walls at the close of the process of thickening, become continuous in a longitudinal row. There is always a constriction at the place of fusion of the cells, thus plainly demarking the vessel segments (Plate VI, Nos. 3, 4, 6). The walls of contact of the segments of a ves- sel are sometimes (a) horizontal, but more often (b) oblique, and fit together exactly; or, again, they may be (c) oblique with a por- tion of the opposed faces united, the pointed and blind ends extend- ing beyond the division wall, as in Liquidambar and Quercus. In (a) the perforation from one segment to another is simple, i.e., with one round opening. In (6) and (c) the perforations are sometimes ECONOMIC WOODS OP THE UNITED STATES 15 simple and sometimes, especially in strongly inclined division walls, scalariform, that is, the opening is crossed with few to many bars in ladder-like arrangement. The bars are usually transverse to the longitudinal axis of the vessel. Both simple and scalari- form perforations may occur side by side in the same wood, but usually one form prevails. These features have considerable diagnostic value. For example, the perforations are simple in Acer, but scalariform in Betula and Cornus; in Msculus and Tilia they are mostly simple, but in Liriodendron and Magnolia scalari- form, except in Magnolia acuminata. Other characteristics of the vessels are the markings on their walls. In most cases they are abundantly pitted with bordered pits, except in contact with parenchymatous cells where the pitting may be either simple or bordered. (See Pits.) It is very common for vessels, particularly the small ones, to be marked with spirals on their interior walls {e.g., Acer, Ilex, Tilia, Ostrya, JZs- culus). In Liquidambar only the pointed ends of the vessel seg- ments are marked with spirals. The function of vessels is to facilitate the ascent of water in the stem. Vessels lose their protoplasmic contents by the time their perforations are complete and become filled with air and water, or air alone. When their activity as water-carriers lessens they frequently become plugged with outgrowths from adjoining parenchymatous cells. (See Tyloses.) In the heartwood of certain species (e.g., Gymnocladus, Gleditsia, Guaiacum, Prosopis) they become wholly or partly filled with gums or resins; in others, with carbonate of lime. The length of vessels is usually very great, and doubtless often equals that of the whole plant. In width vessels exhibit great variation not only in different species, but also in different portions of the same growth ring. In some woods all of the vessels are small (e.g., Tilia, JEsculus [Plate VI, Fig. 5], Populus, Salix); in others they are mostly large (e.g., Juglans); very often, as in Quercus (Plate II, Figs. 5, 6), they vary from large (0.6 mm.*) and conspicuous to very small (0.1 mm.). Vessels in cross section are called pores, and when this term is employed it will be understood to apply to cross sections exclusively. Pores are usually readily distinguishable from the adjoining elements by their larger size, though it is not always * One millimetre is equal to about one twenty-fifth of an inch. 16 ECONOMIC WOODS OF THE UNITED STATES possible to tell small pores from cross sections of tracheids. In outline pores may be round, elliptical, or angular. The first two cases are the rule where the vessel walls are thick enough to resist the pressure of the surrounding elements. This is the case, for example, in the small pores of the red and live oaks (Plate II, Fig. 6), while in the white oaks (Frontispiece; Plate II, Fig. 5) the walls are thin and the pores angular in outline. Sometimes pores are disposed in rings or zones in the early wood of the growth ring, producing ring-porous woods (Plate III) ; in other cases they are scattered singly or in groups throughout the ring or arranged in radial or tangential rows, producing diffuse- porous woods (Plate VI). (See Growth Rings.) In any case the largest pores are almost invariably in the first formed wood of the season. The distribution, size, form, and arrangement of the pores are characters of great importance in classifying woods. References Socereder, H.: Anatomy of the Dicotyledons, Vol. II, p. 1136. Mell, C. D.: History of the Investigations of Vessels in Wood, Proc. Soc. Am. Foresters, Vol. VI, No. 1, 1911, pp. 78-91. DeBary, A.: Comparative Anatomy, pp. 155-171; 503. Mayr, H.: Schlich's Manual of Forestry, Vol. V, 1908, pp. 9-10. Sanio, Carl: Bot. Zeitung, Vol. XXI, No. 15, 1863, pp. 121-128. Hartig, R.: Lehrbuch der Anatomie und Physiologie der Pflanzen, Berlin, 1891, pp. 79-93. TRACHEIDS Tracheids are elongated, spindle-shaped, fibre-like elements, determinate in length and characterized by bordered pits in their side-walls. In the wood of Gymnosperms the tracheid is the dominant element, performing the dual function of conducting water and providing mechanical support for the tree. Bordered pits are mostly confined to the radial walls, except in late wood, and are most abundant near the ends of the tracheids and in one or two rows (Fig. 2, D) . Seen in cross section, the tracheids are polygonal in outline, arranged in radial rows, and, near the periphery of growth ring, with very appreciable increase in thickness of the wall, reduction of the lumen, and tangential flattening (Fig. 8; Plate II, Figs. 1, 2, 4). In a few species, particularly Pseudotsuga, ECONOMIC WOODS OF THE UNITED STATES 17 Taxus, and Tumion, the tracheids are characterized by spiral thickenings on the inner wall. TABLE I LENGTH OF TRACHEIDS IN CONIFEROUS WOODS Botanical Name Abies balsamea " concolor " grandis Chamaecyparis lawsoniana " thyoides . . Larix occiden talis Libocedrus decurrens .... Picea engelmanni " rubens " sitchensis Pinus echinata " edulis " lambertiana " monticola " murrayana " palustris " ponderosa " resinosa " strobus " taeda " virginiana Pseudotsuga taxif olia Sequoia sempervirens " washingtoniana . . Taxodium distichum Thuya occidentalis " plicata Tsuga canadensis " heterophylla Average Maximum Minimum mm. mm. mm. 3.10 4.65 4.15 3.60 2.10 2.60 4.00 5.70 2.95 2.85 5.90 1.95 4.45 4.40 2.65 5.55 3.30 4.05 3.55 3.10 2.75 2.70 7.00 4.80 4.70 2.00 3.85 4.00 3.05 4.20 6.00 5.70 4.35 2.80 3.80 4.70 6.95 3.65 3.70 7.20 2.55 5.85 5.45 3.70 6.70 4.00 4.80 4.55 3.90 3.95 3.30 9.25 5.95 5.80 2.40 4.55 5.05 3.65 2.00 2.75 2.90 2.55 1.45 1.75 3.00 3.05 2.50 2.30 4.40 1.50 2.75 2.75 1.80 3.00 2.50 3.20 3.20 2.55 1.75 1.80 4.05 3.45 3.65 1.40 3.15 2.80 1.75 In certain conifers, particularly Pinus, specialized forms of tracheids of a parenchymatous type are found associated with resin ducts and cysts. They resemble wood-parenchyma cells in form and function, but have bordered pits in their side and end walls. "Resinous tracheids" are ordinary tracheids with deposits of resin usually in the form of thin transverse plates. The tracheids of broadleaf woods (Fig. 2, E) are subordinate 18 ECONOMIC WOODS OF THE UNITED STATES elements often entirely wanting. They are much smaller and less uniform in size and shape than in conifers, and are of most common occurrence in the immediate vicinity of vessels. Their ends are often curved, especially when they terminate just above or below a ray. The walls are usually comparatively thin and bear numer- ous bordered pits very irregularly distributed. Intermediate forms of tracheids are sometimes found which show distinct transition to the vessels in the detailed structure of their walls and in the occasional presence of perforations at the ends of the cells. References Penhallow, D. P.: North American Gymnosperms, pp. 33-58. DeBary, A. : Comparative Anatomy, pp. 164-165. Thompson, W. P. : On the Origin of Ray Tracheids in the Coniferse, Bot. Gazette, Vol. L, 1910, pp. 101-116. Kxy, L.: Ein Beitrag zur Entwickelungsgeschichte der "Tracheiden," Ber. d. deutschen Bot. GeseUschaft, Vol. IV, 1886, pp. 267-276. Sanio, Carl: Botanische Zeitung, Vol. XXI, No. 14, 1863, pp. 113-118. WOOD FIBRES Typical wood fibres (Fig. 2, A, B) are slender, spindle-shaped, sharp-pointed cells with thick walls and narrow cavities. They are further characterized by usually oblique and slit-like simple pits, or less frequently by small, indistinctly bordered pits. Wood fibres are not found in Gymnosperms, but are nearly always present in the wood of Dicotyledons. Wood fibres are of two types, septate and ordinary {non- septate). The septate forms are divided by cross-partitions formed after thickening of the walls has begun. They are of limited occurrence and of relatively small importance. They are characteristic of Swietenia mahagoni and serve as one means of distinguishing the wood from that of certain others closely resembling it. The ordinary forms are very common and are the principal source of strength, hardness, and toughness of broadleaf woods. While their function is largely mechanical, it is probable that they, especially those with bordered pits, play some part, as yet undetermined, in water transportation. Wood fibres exhibit transitional forms from the typical to tracheids on one hand, and to wood-parenchyma strands on the ECONOMIC WOODS OP THE UNITED STATES 19 other. In structure and arrangement they exhibit variations of considerable taxonomic value. For example, in Ilex the fibres are rather thin-walled and marked with spirals and bordered pits, and closely resembling tracheids except for their greater size. In Liquidambar (Plate VI, Fig. 1) the fibres are mostly square in cross section and in rather definite radial arrangement. In * B Fig. 2. — Typical Wood Cells. A, Wood fibre with very narrow lumen; B, wood fibre with larger lumen and showing oblique, slit-like simple pits (s. p.) ; C, end of wood fibre showing saw edge; C, end of wood fibre showing forked .structure; D, ends of two tracheids from Pinus showing numerous bordered pita (b. p.) ; E, Tracheid from Quercus; F, wood-parenchyma strand, showing individual cells and simple pits (s. p.) ; G, chambered wood-parenchyma strand from Juglans, showing crystals of calcium oxalate; H, conjugate parenchyma cells; K, portion of a vessel segment showing simple perforation (p) ; L, portion of a vessel segment showing scalariform perforation (Sc. p.). Greatly enlarged. Robinia (Plate III, Fig. 3) and Toxylon they are in rather large, compact masses in the late wood, separated by groups or bands of pores and parenchyma. In any wood in which they occur they are most abundant in the median portion of the growth ring, and material decrease in the width of a ring is usually at their expense. The ends of most wood fibres are smooth and uniformly 20 ECONOMIC WOODS OF THE UNITED STATES tapering, but sometimes they are flattened, or forked, or with a saw edge (Fig. 2, C, C), adding to the toughness of the wood. Fibres usually run parallel to one another, but in some woods they exhibit a decided interweaving which produces an irregularly grained wood very difficult to split. TABLE II Length of Wood Fibres in Dicotyledonous Woods Botanical Name Acer rubrum Betula nigra Castanea dentata Celtis occidentalis Fagus americana Hicoria alba Ilex opaca Juglans nigra Liquidambar styraciflua Liriodendron tulipifera . Magnolia acuminata . . . Nyssa sylvatica Platanus occidentalis. . . Populus deltoides " grandidentata . " heterophylla. . . " trichocarpa Quercus alba " coccinea " michauxii " rubra " virginiana Salix nigra Tilia americana Ulmus americana Average Maximum mm. mm. .75 1.00 1.80 2.20 1.15 1.45 1.25 1.70 1.20 1.70 1.35 1.70 1.45 2.00 1.10 1.65 1.60 2.00 1.90 2.50 1.75 2.30 1.70 2.35 1.90 2.30 1.40 2.20 1.00 1.35 1.35 1.80 1.15 1.90 1.25 1.50 1.50 2.10 1.55 1.80 1.20 1.45 1.40 1.80 .85 .95 1.15 1.45 1.50 1.90 .50 1.50 .80 1.05 .75 .90 1.15 .65 1.25 1.40 1.00 1.05 1.30 .50 .65 1.00 .50 1.00 1.00 1.10 .70 .85 .45 .85 1.15 References DeBary, A.: Comparative Anatomy, pp. 481-483. Solereder, H.: Anatomy of the Dicotyledons, Vol. II, pp. 1141-1143. Gregory, E. L.: Pores of the Libriform Tissue, Bull Torrey Bot. Club,. Vol. XIII, 1886, pp. 197-204; 233-244. Anonymous: Length of Wood Fibers in Broadleaf Woods, Sc. American Sup., Sept. 30, 1911, p. 211. Sanio, Carl: Bot. Zeitung, Vol. XXI, No. 13, 1863, pp. 89-111. ECONOMIC WOODS OF THE UNITED STATES 21 WOOD PARENCHYMA Parenchyma occurs in the secondary xylem of all woody plants, and, with few exceptions, is disposed in two systems: (1) the vertical, composed of more or less scattered rows of cells forming the wood parenchyma; and (2) the horizontal, made up of plates of cells extending radially and at right angles to the axis — the medullary rays or pith rays. Its chief function is the distribu- tion and storage of elaborated food materials. Typical wood-parenchyma strands (Fig. 2, F; Plate IV, Figs. 5, 6) of Dicotyledons resemble septate wood fibres, but have (1) thinner walls, (2) simple, rounded or lenticular pits instead of oblique, slit-like simple or bordered pits, and (3) cross walls equal in thickness to the lateral walls. The individual cells of a wood- parenchyma strand are mostly short and prismatic, pitted with simple pits and (with the exception of the terminal ones, which are pointed) with transverse or oblique end walls. Between wood fibres and wood-parenchyma strands are intermediate forms without septa — substitute fibres or intermediate wood fibres. Where wood parenchyma borders on large vessels it is usually much flattened as a result of the pressure of the expanding vessel segments. In such locations also are sometimes special forms termed conjugate cells because of flatly tubular processes extending from one to another slightly distant, thus uniting them (Fig. 2, H). There are special forms of wood parenchyma in which the individual cells are divided by cross walls into small chambers of approximately even size which contain solitary crystals, usually of calcium oxalate (Fig. 2, G; Plate IV, Fig. 6). Such crystals are only slightly soluble even in the strongest acids, and are very plainly visible under high magnification in both cross and longi- tudinal sections. Crystals occur in all species of Quercus, though they are commonly more abundant in the five oaks than in decid- uous species. In Juglans (Plate IV, Fig. 6), Hicoria (Plate IV, Fig. 3), and Diospyros, crystals are often quite conspicuous. Calcium-oxalate crystals are also common in ray-parenchyma cells. The distribution and arrangement of wood-parenchyma strands in different species are subject to considerable variation. As seen on cross sections of woody Dicotyledons the cells may be (a) scattered irregularly throughout the growth ring (Plate V, Figs. 3, 5), (6) arranged in tangential lines or bands (Frontispiece, 22 ECONOMIC WOODS OF THE UNITED STATES Plate IV, Figs. 1, 2), (c) terminal, i.e., comprising the outer limit of the growth ring (Plate III, Fig. 6; Plate V, Fig. 2; Plate VI, Fig. 2), (d) surrounding pores (Plate III, Figs. 3, 5), (e) ar- ranged in radial rows. These features are quite important in classifying woods. For example, in Fraxinus americana the pores in the late wood are usually joined tangentially by narrow bands of wood parenchyma, while in F. nigra (Plate V, Fig. 2) the pores are rarely so united. In Hicoria (Plate IV, Fig. 1) wood paren- chyma is in numerous, fine, concentric lines as distinct as the rays, while in Diospyros (Plate IV, Fig. 2) the lines are finer than the rays and very indistinct. In Tilia wood parenchyma is in tangential lines, but is not so disposed in Liriodendron, Magnolia, and Msculus. In Liriodendron (Plate VI, Fig. 2) and Magnolia the outer limit of the growth ring consists of 2-4 rows of tan- gentially flattened wood-parenchyma cells with very thick, copi- ously pitted radial walls. Wood parenchyma is present in the wood of all Gymnosperms except the Taxacece. The cells are invariably associated with resin formation and are usually referred to as resin cells or epithelial cells, according as they are more or less scattered or surrounding resin ducts. Resin cells are usually cylindrical or prismatic, thin-walled, with transverse terminations more or less strongly marked with simple pits. The pits in the side walls are often few and invariably simple. Resin cells can usually be distinguished on cross sections under the microscope by their thin walls, simple pits, or better by the deep color of their contents. If the section passes near enough to an end wall the simple pits therein give the appearance of a sieve plate (Fig. 10). While in most cases resin cells are invisible without the microscope, and often not readily found with it, yet in Juniperus, Taxodium, and Sequoia they are usually conspicuous, not infrequently giving rise in the first two species to wavy tangential lines in the growth ring, visible to the unaided eye. The distribution of the resin cells is variable. In some cases (e.g., Thuya) they are scattering; in others (e.g., Taxodium [Plate II, Fig. 1], Juniperus [Plate II, Figs. 3, 4], Libocedrus) they are disposed in well-defined zones concentric with the growth ring, being most abundant as a rule in the transition zone between early and late wood. In still other cases (e.g., Tsuga) there is often a tendency of some of the resin cells to aggregation, and in ECONOMIC WOODS OF THE UNITED STATES 23 some cases the formation of imperfect resin ducts or resin cysts (Fig. 10). (See Resin Ducts.) In Pinus (Fig. 8) wood parenchyma is found only in association with resin ducts, isolated resin cells being absent; while in Larix and Pseudotsuga resin cells are occasionally found on the extreme outer face of the late wood. In Abies resin cells are remote and inconspicuous; in Thuya plicata they are present, though often zonate in widely separated growth rings, thus often apparently absent. In Sequoia (particularly S. sempervirens) the resin cells are partially filled with dark resin masses which appear on longi- tudinal surface as fine dotted lines, or under lens as rows of black or amber beads. References DeBary, A.: Comparative Anatomy, pp. 4S5-4S6. Penhallow, D. P.: North American Gymnosperms, pp. 109-122. Boulger, G. S.: Wood, pp. 28-29. Sanio, Carl: Bot. Zeitung, Vol. XXI, No. 12, pp. 93-98. Kny, L.: Ueber Krystallbildung beim Kalkoxolat, Berichte der deutschen Bot. Gesellschaft, Vol. V, 1887, pp. 387-395. RAYS Medullary or pith rays, for brevity termed simply rays, appear on the cross section of a stem as radial lines crossing the growth rings at right angles and extending into the bark (Fig. 1). A few of them originate at the pith and are commonly known as primary rays. Successively, as the stem increases in size, addi- tional or secondary rays arise between those already formed. A ray may arise in the cambium layer at any point, and once formed its growth is continuous.* Under the microscope the line formed by the ray becomes a radial series of mostly elongated cells usually with transverse end walls (Plates II-IV). Viewed radially a ray appears as a muriform structure composed of from one to many tiers of brick- shaped cells (Plate IV, Figs. 5, 6). In tangential section the ends of the rays are visible, showing to advantage their height, shape, * When on cross or radial sections a ray appears to be discontinuous, it is probable that it has merely been missed by the plane of section. This empha- sizes the importance of making cross sections exactly at right angles to the axis of growth, and radial sections as nearly as possible parallel with the rays. jlvvmh aimjohj 24 ECONOMIC WOODS OF THE UNITED STATES width, and distribution, and also the outline in cross section of the component cells (Plate III, Fig. 1; Plate IV, Figs, 3, 4; Plate VI, Figs. 3, 4, 6). Ray cells are usually elongated in the radial direction. This is normally the case in Gymnosperms and usually so in the woody Dicotyledons. Not infrequently in the latter, however, part or all of the cells are upright, i.e., with their greatest diameter vertical, or are square. The marginal cells are sometimes upright and the interior cells radially elongated or procumbent (Fig. 3). The upright cells are often very irregular, especially the outermost marginal rows; sometimes they are nearly square; again they are in pali- sade arrangement. When these upright or square cells are in Fig. 3. — Radial sections of heterogeneous rays. A, Sassafras sassafras (sassa- fras) ; B, Nyssa sylvatica (black gum); C, AZsculus octandra (buckeye), showing large pits (I. p.) in upright cells (up. a), where they adjoin vessels; and small pita (s. p.), in procumbent cells (pr. c). No pits are shown in A and B. Magnified about 150 diameters. contact with large vessels the separating walls are characteristically marked with very large pits whose polygonal or oval outlines present the appearance of lattice work (Fig. 3, C). The lateral walls of similarly located procumbent cells usually contain few small pits. Moreover, in proximity to large vessels the walls between all ray cells are usually thicker and much more abun- dantly pitted than elsewhere. Upright cells are not always easy to distinguish from the cells of wood-parenchyma fibres, especially where they cross the latter, on account of the similar direction of their longitudinal diameters. ECONOMIC WOODS OF THE UNITED STATES 25 Rays consisting wholly of procumbent cells may be said to be homogeneous; those which contain both upright and procumbent cells, heterogeneous (Fig. 3) . Heterogeneous rays are characteristic of many dicotyledonous woods, and are features of importance in classification. For example, Celtis has heterogeneous rays, while those of Ulmus are homogeneous. The same distinction obtains between Salix and Populus, Sassafras and Fraxinus. The rays of Sassafras are peculiar in having a few of the marginal cells abnor- mally large and rounded or ovate (Fig. 3, A). The rays in the wood of Gymnosperms are for the most part one cell wide, i.e., uniseriate, and from 1 to 20 cells high. It is not r.tr. r.p._ r.tr. Fig. 4. — Radial section of ray of Pinus strobus (white pine) ; showing the smooth upper and lower walls of the ray tracheids (r. ir.), and the presence in the lateral walls of the ray-parenchyma cells (r. p.) of large simple pits (s. p.), com- municating with the wood tracheids (w. tr.) adjacent; b. p., bordered pits. Magni- fied about 250 diameters. uncommon to find biseriate rays, and those which contain resin ducts (Pinus, Picea, Larix, Pseudotsuga) are multiseriate. The latter, because of their shape as seen on tangential section, are called fusiform rays (Fig. 9) . In woody Dicotyledons there is more variation in the rays. In some instances {e.g., Msculus [Plate VI, Fig. 6], Salix, Populus) low uniseriate rays only are present. At the other extreme is Quercus (Plate III, Fig. 1), where the largest rays are from 25 to 26 ECONOMIC WOODS OF THE UNITED STATES 75 cells wide and several hundred high. These large rays give rise to the handsome figure of quarter-sawed {i.e., radially cut) oak lumber. Besides the large rays in Quercus there are numerous intermediate ones, mostly uniseriate and 1-20 cells high (Plate III, Fig. 1). In Platanus the rays are uniformly broad (10-15 cells), while in Fagus only a portion of the rays are broad (15-25 cells), the intermediate ones being uniseriate. In some of the evergreen oaks, Carpinus and species of Alnus (Plate V, Figs. 3, 4), the large rays appear to be composed of numerous small ones r.tr Fig. 5. — Radial section of a ray of Pinus edulis (piflon pine), showing the smooth upper and lower walls of the ray tracheids (r. tr.), and the presence in the lateral walls of the ray-parenchyma cells (r. p.) of small semi-bordered pits (s. b. p.), communicating with the wood tracheids (w. tr.) adjacent; s. p., simple pit; b. p., bordered pit. Magnified about 250 diameters. separated by wood fibres. Such rays are termed aggregate or compound rays; sometimes also false rays. Every ray, regardless of its width at the middle, tapers to an edge so that the upper and lower margins are a single cell wide.* The comparative distinctness which rays on cross section present to the unaided eye is important in separating certain woods which bear superficial resemblance. For instance, the For this reason cross sections often do not afford a correct idea of ray width. ECONOMIC WOODS OF THE UNITED STATES 27 rays in Sassafras are much more distinct than in Fraxinus; like- wise in Celtis and Ulmus, Tilia and JZsculus, Acer and Betula. In white oaks the height of the large rays averages considerably greater than in the red or live oaks. In dicotyledonous species the rays are composed wholly of parenchyma. In certain Gymnosperms (Pinus, Larix, Picea, Pseudotsuga, Tsuga, and occasionally in others) ray tracheids are present (Figs. 4-7). They are usually marginal, but often inter- spersed and sometimes they compose entire rays, particularly Fig. 6. — Radial section of a ray of Pinus resinosa (red or Norway pine), showing the dentations (d) or reticulations on the upper and lower walls of the ray tracheids (r. tr.), and the presence in the lateral walls of the ray-parenchyma cells (r. p.), of large simple pits (s. p.) communicating with the wood tracheids {w. tr.) adjacent; b. p., bordered pit. Magnified about 250 diameters. low ones. They can be distinguished from the ray-parenchyma cells by the presence of bordered pits in the lateral and especially the end walls. They are often irregular in outline and are devoid of visible contents. They have their counterparts in the paren- chymatous tracheids surrounding the epithelial cells of resin cysts and ducts. In the young root, and sometimes in the young stem as well, special upright or oblique forms occur which may be considered as transitional from wood tracheids to ray tracheids. The character of the upper and lower walls of the ray tracheids, whether smooth, as in soft pines, or dentate or reticulate, as in 28 ECONOMIC WOODS OF THE UNITED STATES pitch pines, affords a constant diagnostic feature of much im- portance in separating the two great groups of Pinus (Figs. 4-7). Ray-parenchyma cells in general communicate with each other, with the ray tracheids, and with the adjacent wood elements by means of pits always simple in the wall of the parenchyma cell, r.tr Ir^f- Fig. 7. — Radial section of a ray of Pinus palustris (longleaf pine), showing the dentations (d) or reticulations on the upper and lower walls of the ray tracheids (r. tr.J, and the presence in the lateral walls of the ray-parenchyma cells (r. p.) of small simple pits (s. p.), communicating with the wood tracheids (w. tr.) adjacent; b. p., bordered pit. Magnified about 250 diameters. but commonly more or less bordered in the other. Often certain cells of a ray have thicker vvalls and more numerous pits than the others. References Penhallow, D. P.: North American Gymnosperms, pp. 78-108. Bailey, I. W.: On the Origin of the Broad Ray in Quercus, Bot. Gaz., Vol. XLIX, No. 3, March 1910, pp. 161-167. : Notes on the Wood Structure of the Betulacese and Fagaceae, Forestry Quarterly, Vol. VIII, No. 2, 1910, pp. 178-185. : The Relation of Leaf -Trace to Compound Rays in Lower Dicotyledons, Annals of Botany, Vol. XXV, No. 97, January 1911, pp. 225-241. Groom, Percy: The Evolution of the Annual Ring and Medullary Rays of Quercus, Annals of Botany, Vol. XXV, No. 100, October 1911, pp. 983-1004. ECONOMIC WOODS OF THE UNITED STATES 29 Thompson, W. P. : On the Origin of the Multiseriate Ray of the Dicotyledons, Annals of Botany, Vol. XXV, No. 100, October 1911, pp. 1005-1014. : The Origin of Ray Tracheids in the Coniferse, Bot. Gaz., Vol. L, No. 2, 1910, pp. 101-116. Kny, L.: Beitrag zur Kenntnis der Markstrahlen dicotyler Holzgewachse, Berichte d. deutschen Bot. Gesellschaft, Vol. VIII, Berlin, 1890, pp. 176-188. Essner, Benno: Ueber den diagnostischen Werth der Anzahl und Hohe der Markstrahlen bei den Coniferen, Halle A. S., 1882. See also Bot. Centralblatt, Vol. XII, No. 12, 1882, pp. 407-408. Zijlstra, K. : Die Gestalt der Markstrahlen in sekundaren Holze, Rec. Trav. bot. neerl., V, 1908, pp. 17-20. RESIN DUCTS Resin ducts are long, narrow, intercellular channels surrounded by parenchyma cells and rilled with resin (Fig. 8). Unlike vessels, they have no walls of their own, but are limited by a layer of cells called epithelium. The epithelial cells are thin-walled in Pinus and mostly thick-walled in Larix, Picea, and Pseudotsuga. When thick-walled the cells are rounded and show clearly in cross sec- tion, while those with thin walls are compressed and very likely to be torn in sectioning. Resin cysts are very short, duct-like, intercellular spaces very common in Sequoia, Tsuga, and Abies. Not infrequently they are in longitudinal series, but differ from a true duct in having numerous constrictions. Resin ducts are largest and most abundant in Pinus, where they are fairly well distribut :d throughout the growth ring, though usually more numerous in the transition zone between early and late wood. They are comparatively large in most species, averag- ing about 0.25 mm., and are readily visible to the unaided eye. On longitudinal surface they appear as long, delicate lines like pin scratches, filled with resin. In Larix, Picea, and Pseudotsuga the ducts are smaller, sometimes invisible without lens, fewer in number, and irregularly distributed, often more or less grouped. In addition to the ducts extending in a vertical direction, there are horizontal ducts in the fusiform rays (Fig. 9) . The two series are united at infrequent intervals. Resin ducts very commonly develop as a result of injury, not only in genera in which they occur normally, but also in others 30 ECONOMIC WOODS OF THE UNITED STATES (e.g., Tsuga, Abies, Sequoia) where normally absent. The formation of these traumatic resin ducts, as they are called, following wound- ing by chipping of the outer layers of the sapwood of Pinus palustris, is the source of most of our turpentine and other naval stores. Traumatic ducts can be distinguished from normal ones l.w. Fig. 8. — Cross section through a portion of two growth rings of Pinus ponderosa (western yellow pine); r. d., resin duct; e., epithelial cells; r., ray; e. w., early wood; I. w., late wood; b. p., bordered pit. Magnified about 200 diameters. by their peculiar localization, usually, as seen on cross section, forming one or more compact rows concentric with the growth ring (Fig. 10). Gum ducts occur sporadically in the woods of certain indigenous Dicotyledons, viz., Liquiolambar, Swietenia and Prunus. ECONOMIC WOODS OF THE UNITED STATES 31 In Leitneria floridana numerous resin ducts are found at the margin of the pith, but are not in the wood. The epithelial cells are thick-walled and in a single layer. Resin ducts are features of great system- atic importance. Their presence in Pinus, Picea, Larix, and Pseudotsuga serves as an ade- quate basis for separating the woods of these four genera from other Gymnosperms. Their relative size, distribution, and occurrence, and the character of the epithelium, whether thick or thin-walled, are features made use of in specific diagnoses. References Penhallow, D. P.: North American Gymnosperms, pp. 109-153. Kirsch, Simon : The Origin and Development of Resin Canals in the Coniferse with Special Reference to the Development of Tyloses and their Co- relation with the Thylosal Strands of the Pteri- dophytes, Proc. Royal Soc. of Canada, 1911. Foxworthy, Fred W.: Philippine Dipterocarpacese. Phil. Journal of Science, C. Botany, Vol. VI, No. 4, Sept. 1911, pp. 231-287. Solereder, H. : Anatomy of the Dicotyledons, Vol. II, pp. 1101-1102. Tschirch, A.: Die Harze und die Harzbehalter, Vol. II. n \r.t. All wood elements when first formed are limited by a very thin cellulose membrane, the primary wall. Subsequent development involves an internal thickening which is com- posed very largely of lignin, the secondary wall. This thickening may proceed uniformly, or, as is usually the case, small gaps, called pits, occur. A pit is merely an unthickened portion of the cell wall. Pits are of two principal types, simple and bordered (Fig. 11). Fig. 9. — Tangen- tial section of a fusi- form ray from Pinus ponderosa (western yellow pine); r. d., horizontal resin duct; e., epithelial cells; r. t., ray tra- cheids; the remain- der of the cells are ray-parenchyma cells. Magnified about 200 diameters. 32 ECONOMIC WOODS OF THE UNITED STATES Intermediate forms exist whose reference to either group is . arbitrary. A simple pit is one in which the thickening about a spot on the primary wall forms a canal which is equally wide throughout its length, or narrowing outward (Fig. 11, H). The length of the canal is determined by the thickness of the secondary wall. When simple pits occur in very thick-walled cells, there is often a tend- ency to a slight funnel-formed enlargement of the canal toward cocoon Fig. 10. — Cross section of a wound area in Tsuga canadensis (eastern hemlock) showing five traumatic resin ducts (tr. r. d.), in tangential row. Note thick-walled epithelial cells (e), and occasional resin cells (r. c), showing sieve-like end walls. Magnified about 150 diameters. the primary wall. Often the canal widens sufficiently to present the appearance of a narrow border (Fig. 11, G). Seen in profile, as in section, the pit canal of such a pit is narrow at the end toward the centre of the cell, but widens gradually outward. A bordered pit is one in which the canal widens suddenly, that is, with a distinct angle, toward the primary wall (Fig. 11, A). In surface view a bordered pit appears as a bright spot or slit within a circle or ellipse (Fig. 11, B). This outer circle marks the limit of the unthickened area; the bright spot is the inner opening or aperture of the canal; the zone between the two is called the border. Pits, especially bordered ones, usually are paired on opposite sides of the primary-cell walls. Pits between vascular elements are invariably bordered; between parenchymatous elements, invariably simple; between vascular and parenchymatous, they may be simple, but more frequently are semi-bordered, that is, ECONOMIC WOODS OF THE UNITED STATES 33 bordered in the vessel or tracheid, and simple in the adjacent parenchyma cells (Fig. 11, F). Pits in typical wood fibres are simple and slit-like, and usually in oblique position (Figs. 11, K; 2, B). In many cases, however, where the fibres resemble tracheids their pits are more or less bordered. The fibres of the bast have only simple pits. The shape of the border is commonly circular, but may be •oval, lenticular, oblong, or, in the case of dense aggregation, polyg- onal. Scalariform markings found on the vessel walls in certain Fig. 11. — Schematic representation of pits, greatly enlarged. A, section of "bordered pit showing cell walls (c. w.), primary cell wall (p. c. w.), pit canal (c), torus (J) ; A', the same with torus (0 shoved to one side and lying lid-like against the aperture of the pit canal; B, surface view of bordered pit shown in A or A', showing aperture (a) and border (6) ; C, surface view of bordered pit with lentic- ular aperture (a) , the crossed appearance being due to the fact that the apertures on opposite sides of the pit are shown; D, surface view of a bordered pit with slit-like aperture (a) , common in thick-walled tracheids of late wood in gymnosper- mous woods; E, surface view of scalariform bordered pit with narrow, elongated aperture (a) and border (b) ; F, section of a semi-bordered pit showing border on one side only; G, simple pit with funnel-formed canal and appearing slightly bordered in surface view; H, ordinary simple pit with canal (c) uniform or narrow- ing outward (i.e., toward primary cell wall); K, surface view of slit-like pit com- mon in wood fibres. woods (i.e., Magnolia [Plate VI, Fig. 3], Hamamelis and Liquid- ambar in part) are merely much-elongated bordered pits which appear as horizontal clefts with only narrow portions of the wall between them (Fig. 11, E). The pit cavities of two adjacent pits are separated by the primary wall which persists as a limiting membrane (Fig. 11, p.m.). 34 ECONOMIC WOODS OF THE UNITED STATES This membrane, which is really made up of two membranes of contiguous cells which have become united in development, is very thin toward the border of the pit, but usually thickened near the centre. This thickened portion is called the torus (Fig. 11, t). The pit membrane very frequently increases in size and bulges out so that the torus lies lid-like against the aperture of the pit canal (Fig. 11, A'). A sieve-like structure of the pit membranes has been observed in the bordered pits of the vessels in certain species.* Between the bordered pits on the radial walls of the tracheids of Gymnosperms it is very common to find folds of cellulose, which, when properly stained, are quite conspicuous under the compound microscope. These folds, which appear as horizontal or more or less semi-circular markings, sometimes doubled, are most abundant in the thin-walled tracheids of the early wood. They are without diagnostic value. The apparent function of pits is to facilitate the passage of some part of the cell contents from one cell to another. Bordered pits are mostly associated with water transfer, and simple pits with the distribution of elaborated food. Pits are of considerable value for systematic purposes. For example, in the white pines and Pinus resihosa, the radial wall of each ray-parenchyma cell shows one or two large simple pits communicating with each adjacent wood tracheid, while in the foxtail and nut pines and in the hard pines there are three to six rather small pits so communicating (Figs. 4-7) . The presence of pits in the tangential walls of the tracheids of the late wood in soft pines, and their absence in similar location in the pitch pines, serve as an additional point of distinction between these two great groups. While the pits in the radial walls of the tracheids of Gymno- sperms are usually in a single row, they may occur in biseriate or triseriate arrangement. In the larger tracheids of Tsuga they are mostly biseriate. In Taxodium distichum they are characteris- tically crowded, flattened, and often irregularly arranged. In dicotyledonous woods as a whole, pits are much smaller and less regular in their distribution than in Gymnosperms. The * Jonsson, Bengt. : Siebahnliche Poren in den trachealen Xylemele- menten der Phanerogamen, hauptsachlich der Leguminosen, Berichte d. deutschen Botanischen Gesellschaft, Vol. X, 1892, pp. 494-513. ECONOMIC WOODS OF THE UNITED STATES 35 nature of the pits, whether simple or distinctly bordered, in the walls of the wood fibres, and the character of pitting where vessels are in contact with wood parenchyma or the rays, are often helpful in classification. Scalariform bordered pits in the walls of the vessels of Magnolia (Plate VI, Fig. 3) serve to distinguish this genus from Liriodendron (Plate VI, Fig. 4), in which they are absent or very sparingly developed. References DeBary, A.: Comparative Anatomy, pp. 158-164. Gregory, E. L.: The Pores [Pits] of the Libriform Tissue, Bui. Torrey Bot. Club, N. Y., Vol. XIII, 1886, pp. 197-204; 233-244. Penhallow, D. P.: North American Gymnosperms, pp. 59-77. Solereder, H. : Anatomy of the Dicotyledons, Vol. II, pp. 1139-41. Gerry, Eloise: The Distribution of the "Bars of Sanio" in the Coniferales, Annals of Botany, Vol. XXIV, No. 93, January 1910, pp. 119-123. Kreuz, J. : Die gehoften Tiipfel des Xylems der Laub- und Nadelholzer, Sitzb. d. Akad. Wiss., Wien, Vol. LXXVI, Part. 1, 1878, pp. 353-384. Russow, E. : Zur Kenntnis des Holzes, insonderheit des Coniferenholzes, Bot. Centralblatt, Vol. XIII, Nos. 1-5, 1883. It is not uncommon to find the vessels of many Dicotyledons (Plate III, Figs. 3, 4) and the resin ducts of certain Gymnosperms more or less completely filled with pith-like cells called tyloses. Usually the walls of the tyloses are very thin, but exceptions occur (e.g., Robinia and Toxylon) where they may be considerably thickened, sometimes becoming sclerotic. Tyloses in large vessels are plainly visible to the unaided eye, their high lustre giving them the appearance of froth. Tyloses are cells which have developed from protrusions of the wood or ray parenchyma into the lumen of a vessel or the canal of a duct or an intercellular space. Their formation is apparently due to differences in pressure within the parenchyma cells and the vessels or ducts they adjoin. After vessels lose their sap they are no longer turgid, in fact the air within them becomes rarefied. In consequence of this reduction of pressure the neighboring paren- chyma cells rupture or disorganize the limiting membranes of the pits, thereby rendering the lumen of the vessel available for their further extension and development. This explains why tyloses do not occur in vessels which are in a state of activity, but as a 36 ECONOMIC WOODS OF THE UNITED STATES general rule arise in the inner region of the sapwood, i.e., in the wood where the vessels are losing their power of conduction. Once inside the vessel, the intruding cells rapidly divide and grow until the space is filled or their food-supply is exhausted, and thus form a parenchymatous tissue in which carbohydrates may be stored. The effect of the formation of tyloses is to block up the vessels and render the heartwood impervious, or nearly so, to the entrance of fluids. Tyloses are especially abundant in the vessels of white oaks (Frontispiece), thus adding to the technical value of the wood for cooperage. This feature is also of some value in sepa- rating the white from the black oaks, since in the latter group tyloses are rather scarce or wanting (Plate II, Fig. 6) . In Quercus marilandica, however, tyloses are abundant. Tyloses also occur occasionally in the tracheids of the wood of Gymnosperms, particularly in the wood of the roots. Tyloses in resin ducts are characteristic of Pinus and (in less degree) Picea, but are sparingly developed or absent in Larix and Pseudotsuga. References Kirsch, Simon: On the Development and Function of Certain Structures in the Stipe and Rhizome of Pteris aquilina and Other Pteridophytes, Trans. Royal Soc. of Canada, 3d Series, Vol. I, sec. iv, Ottawa, 1908, pp. 403-8. DeBary, A.: Comparative Anatomy, p. 170. Sachs, Julius: Lectures on the Physiology of Plants (trans, by H. Marshal Ward), p. 581. Chrysler, M. A.: Tyloses in Tracheids of Conifers, New Phytologist, No. 7, 1908, pp. 198-204. Golden, K. E.: Tyloses in Brosimum aubletii, Proc. Ind. Acad. Sci., 1904, pp. 227-232. von Alten, H. : Kritische Bemerkungen und neue Ansichten iiber die Thyllen, Bot. Zeitung, Vol. LXVII, 1909, pp. 1-23. Raatz, Wilhelm : Ueber Thyllenbildungen in den Tracheiden der Conif eren- holzer, Ber. d. deutschen Bot. Gesellschaft, Vol. X, 1892, pp. 183-192. PITH FLECKS OR MEDULLARY SPOTS Pith flecks or medullary spots are small, brown or grayish, half-moon-shaped patches appearing so commonly on the cross sections of many diffuse-porous woods, especially of the four families Salicacem, Betulacece, Rosacece, and Aceracece. On longi- ECONOMIC WOODS OF THE UNITED STATES 37 tudinal sections of a stem the pith flecks appear as flattened strands running up and down the stem, and often into the root. Examined microscopically, pith flecks are seen to be made up of irregularly shaped, polyhedral, parenchymatous cells with thick, dark- colored walls copiously pitted with simple pits. At certain seasons the cells are filled with starch grains. Pith flecks have a pathological origin. They are due to the work of cambium miners whose tunnels are filled by the tylosal development of adjacent uninjured parenchyma cells, especially of the cortex. The dissolved cell fragments and larval excrement are pressed into a narrow border by the rapid growth and division of the "filling cells." This feature has frequently been used for purposes of classifi- cation, principally because of the failure to understand its exact nature. It has been noted in a large number of woods, but is by no means constant in its occurrence. Some stems, for example, contain numerous pith flecks, while other individuals of the same species in the vicinity, or even from the same root stock, do not show them. Furthermore, in stems with pith flecks certain growth rings may be free of them, while others of the same section are thickly dotted, or the lower portion of the stem may contain them and the upper be entirely free. Taken in connection with other features, however, the presence of pith flecks in abundance may serve to indicate the species. For example, they are usually very numerous in Betula populifolia and B. papyrifera, and infrequent in B. lenta, B. lutea, and B. nigra, numerous in Acer rubrum and A. saccharinum, but usually want- ing in A. saccharum. References Record, S. J.: Pith Flecks or Medullary Spots in Wood, Forestry Quarterly, Vol. IX, No. 3, 1911, pp. 244-252. Grossenbacher, J. G.: Medullary Spots: A Contribution to the Life History of Cambium Miners, Tech. Bui. No. 15, N. Y. Agri. Exp. Sta., Geneva, N. Y., 1910. Von Tubeuf, Karl F.: Die Zellgiinge der Birke und anderer Laubholzer, Forstlich-naturw. Zeitschrift, VI. Jahrgang, 1897, pp. 314-319. Also Naturw. Zeitschrift f. Forst- und Landwirtschaft, 6. Jahrgang, 1908, pp. 235-241. Kienitz, M.: Die Entstehung der " Markflecke," Bot. Centralblatt, Vol. XIV, 1883, pp. 21-26; 56-61. 38 ECONOMIC WOODS OF THE UNITED STATES trabecule: sanio s beams In radial and cross sections of the wood of all Gymnosperms it is not uncommon to find small bars stretched across the lumina of the tracheids from one tangential wall to another. Occasionally they appear in isolated tracheids, but usually traverse in the same direction the entire length of a long radial series (Fig. 12). While the most common form of bar is a simple cylinder slightly enlarged at the points of contact with the cell wall, they may occur as Iff™ ® 1 © n® rliyirill B Fig. 12. — Trabecule in Pinus murrayana (lodgepole pine). A, cross section showing tracheids with beams (tr.) crossing the middle row in tangential series; B, radial section showing beams (tr.) which become wider in late wood. Magnified about 150 diameters. double bars or as constricted plates. These bars, which were first described by Sanio (loc. cit.), originate in the cambium and result from the partial resorption of folds in the cell wall. Their function is unknown. Owing to their general distribution through- out all species of Gymnosperms they are without taxonomic value. References Sanio, Carl: Botanische Zeitung, Vol. XXI, No. 14, 1863, p. 117. Muller, Carl: Ueber die Balken in den Holzelementen der Coniferen, Bericht ii. d. Verhandlungen d. achten General-Versammlungen d. deutsehen Botanischen Gesellschaft, 1890, pp. (17) to (46). Raatz, Wilhelm: Die Stabbildungen in secundaren Holzkorper der Baume und die Initialentheorie, Jahrb. fur Wissenschaftliche Botanik, Vol. XXIII, 1892, pp. 567-636. ECONOMIC WOODS OF THE UNITED STATES 39 RIPPLE MARKS There are numerous woods which present on longitudinal sec- tion (particularly the tangential) fine, delicate cross lines or stripes sometimes called "ripple marks." The distance between these markings varies from 0.11 to 0.50 mm., and is fairly constant for a species. On some woods (e.g., /Esculus octandra, Swietenia mahagoni, and Diospyros virginiana [Plate IV, Figs. 4, 5]), these lines are very clear and distinct to the unaided eye; on others {e.g., Tilia americana, T. pubescens, and T. heterophylla) they are near the limit of vision, or again, they are invisible without the lens. In most species showing these markings the feature is con- stant and of considerable importance for diagnostic purposes, though in a few species (e.g., Swietenia mahagoni) the same piece of wood may show the markings in one place and not in another. This cross-striping of a wood is due (1) to the arrangement of the rays in horizontal series, or (2) to the tier-like ranking of the wood fibres, vessel segments, or other elements, or (3) to a combination of (1) and (2) (Plate IV, Figs. 4, 5). The lines resulting from the horizontal seriation of the rays is usually more conspicuous and of more common occurrence than those in (2). In the combination of the two forms, which is very common, the junction of the vessel segments or of the fibres is usually between the rays (Plate IV, Fig. 5). This peculiar arrangement of wood elements is also evidenced on cross section. Where the rays are in perfect horizontal seriation a section between two tiers shows an entire absence of rays. In most instances, however, it results in gaps of irregular width, depending upon the regularity of the stories. Where the rays are much wider near the middle than at the margin, their apparent width when viewed transversely will show considerable variation, according to the relative location of the plane of sec- tion. Where the fibres are arranged in tiers, their apparent size is affected in a similar manner. References Record, S. J.: Tier-like Arrangement of the Elements of Certain Woods, Science, January 12, 1912, pp. 75-77. Von Hohnel, Franz Ritter: Ueber stockwerkartig aufgebaute Holzkorper. Sitzb. d. Math. Naturw. Classe d. kaiserlichen Akademie d. Wissen- schaften, Vol. LXXXIX, Part 1, Wien, 1884, pp. 30-47. 40 ECONOMIC WOODS OF THE UNITED STATES Von Hohnel, Franz Ritter: Ueber den etagenformigen Aufbau einiger Holzkorper, Berichte d. deutschen Bot. Gesellschaft, Vol. II, Berlin, 1884, pp. 2-5. GROWTH RINGS A tree increases in diameter by the formation between the old wood and the inner bark of new woody layers which envelop the entire stem and living branches. In cross section, as on the end of a log, these layers appear as concentric zones or rings (Fig. 1). The distinction between contiguous rings is due to structural peculiarities, augmented in some instances by local deposit of resin or pigment. Each ring consists of two more or less readily distinguishable parts, the inner, called early wood (spring wood), and the outer, or late wood (summer or autumn wood). In ring-porous woods (Frontispiece; Plate III), such as Quercus, Castanea, Fraxinus, and Robinia, the larger vessels become local- ized in the early wood, thus forming a region of more or less open and porous tissue, while the wood fibres preponderate in the late wood, thereby producing a much denser layer. In other instances, as in Acer, Magnolia, JEsculus, and Liquidambar (Plate VI), where the vessels are fairly uniformly distributed — diffuse-porous — the occurrence of growth rings may be due to one or more of the following conditions: (1) a gradual diminution in size of the vessels toward the periphery of the ring; (2) a decided reduction in number of the vessels in the late wood; (3) a change in kind of the wood elements, e.g., where the outer layer of late wood consists wholly or chiefly of wood parenchyma or of tracheids; (4) increase in thickness of the wall of the wood elements near the limit of the late wood. In Gymnosperms where vessels are wholly absent growth rings are due to variations in the tracheids. Viewed in cross section the cells of early wood are relatively large, thin-walled, and more loosely aggregated; while those of the late wood are smaller, thicker-walled, closely packed together and very often radially flattened, presumably as a result of cortical pressure (Fig. 8; Plate II, Figs. 1, 2, 4). This transition from open to dense structure may be gradual, as in the soft pines, or very abrupt, as in many hard pines. Not infrequently the dense aggregation of cells involves a deepening of the color peculiar to the tissue as a whole. In any wood it is almost invariably the apposition of the more open ECONOMIC WOODS OF THE UNITED STATES 41 early wood to the face of the more compact late wood that serves to define the zones of growth. The origin of growth rings is physiological. Plants, like animals, seem incapable of indefinitely sustained activity, but require periods of recuperation. In latitudes of decided seasonal changes such periods of rest are provided by the alternation of the seasons, in which case the zones of growth correspond very closely with annual periods. This constancy of relation diminishes towards the equator and, although in the tropics growth rings are not uncommon, they provide no reliable index to the age of the tree. In temperate climates trees occasionally produce secondary or false rings, usually attributable to some disturbance of the normal course of growth of the season, such as the action of frost, drought, hail, and insect damages. Such rings, however, can usually be distinguished from annual rings by their less pronounced line of demarcation. Variation in width of different growth rings is common to all trees, and is determined by external conditions of light, heat, moisture, and available food-supply. The cross section of a stem presents in the variable form and size of its rings a history of its growth and nutrition. The breadth of an individual growth ring may not be uniform all round in consequence of unequal acceleration of the growth on different sides, the ring thus becoming undulating or eccentric. The growth centre is accordingly not coincident with the geometric centre. The more nearly erect the stem and the more nearly per- fect the crown, the more closely will the two centres coincide. In some species {e.g., Carpinus caroliniana and Juniperus virginiana) , irregularity of growth causes the trunks to become fluted or even deeply scalloped. The growth rings near the centre of a stem usually exhibit considerable difference in structure from those later formed. The elements are usually thinner-walled, of shorter length, and less densely aggregated, so that the inner core of wood is comparatively soft and weak. In the wood of Dicotyledons, although the elements characteristic of the species are all present, their characteristic ar- rangement does not appear clearly until later. This is particularly evident in the distribution of the vessels and wood parenchyma in many woods. Consequently, in the employment of these features for systematic purposes, it is important to use stems of consid- erable thickness rather than small branches or young shoots. 42 ECONOMIC WOODS OF THE UNITED STATES In ring-porous woods of good growth it is usually the middle portion of the ring in which the thick-walled, strength-giving fibres are most abundant. As the breadth of the ring diminishes, this middle portion is reduced so that very slow growth (fine grain) produces comparatively light, porous wood composed Fig. 13. — Quercus macrocarpa (bur oak) : cross section through three entire growth rings showing very large pores in early wood and general absence of dense- walled wood. fibres. Such wood is light, soft, and not strong. Magnified 20 diameters. (From Bui. 102, U. S. Forest Service.) Fig. 14. — Quercus macrocarpa (bur oak) : cross section through one entire growth ring and parts of two others, showing comparatively small pores (v) in early wood (e. w.), and presence of abundant thick-walled wood fibres in the late wood (I. w.). Such wood is heavy, hard, and strong. Magnified 20 diameters. (From Bui. 102, U. S. Forest Service.) mostly of thin-walled vessels and wood parenchyma (Figs. 13, 14). This explains why "second-growth" (i.e., rapidly grown) hickory, ash, and chestnut are stronger than the slowly grown "virgin" stock of the same species. Moreover, in trees of this type there is less early wood formed at the base of a stem than farther up, ECONOMIC WOODS OF THE UNITED STATES 43 because growth begins considerably later at the base. The strongest, densest, and toughest timber is that grown in the open where conditions are favorable to rapid growth. In diffuse-porous woods, such as Acer, Betula, Liriodendron, and Fagus, there seems to be no definite relation between ring width and density. In Gymnosperms, as a rule, wood of medium to fine grain contains a greater proportion of late wood and con- sequently possesses greater weight and strength than when very fine or very coarse grained. In this connection the following statement of H. Mayr * is interesting: "Assuming identity of soil, the specific weight and hardness of wood decreases with distance from the optimum climate of its production both toward cooler or warmer climates. It is indifferent whether the annual zones consequently increase or decrease in breadth, or whether the wood is broadleaved or coniferous. Within the natural habitat of any tree the centre of its habitat produces the heaviest and hardest wood." Various theories have been advanced to explain the formation of early and late wood. Penhallow (following Sachsf) says that the elements of the early wood are "formed under a minimum tension in consequence of which they rapidly attain to relatively great size, and it is therefore found that the first tissue of the season is always most open. In consequence of the great excess of nutrition supplied during this period of growth, and the very rapid process of construction which follows, secondary growth of the walls is limited, and these structures remain thin, while the lumens are correspondingly large." R. Hartig maintains that the thin-walled early wood is due to poorer nutrition and the necessity of forming conductive tissue, while thick-walled late wood results from better nutriment during the warm and sufficiently moist summer. Wieler, on the other hand, claims that the more unfavorable the conditions of nutri- tion, the slower the development of assimilating organs, hence the more late wood. References Penhallow, D. P.: The Relation of Annual Rings to Age, Can. Records of Sci., Vol. I, p. 162. : North American Gymnosperms, pp. 24-32. DeBary, A.: Comparative Anatomy, pp. 475-478; 500-507. *Schlich's Manual of Forestry, Vol. V, rev. ed., p. 54. t Text-Book of Botany, p. 575, foot-note. 44 ECONOMIC WOODS OF THE UNITED STATES Roth, Filibert: Timber, Bui. 10, U. S. Div. of Forestry, pp. 14-16. Zon, Raphael: Methods of Determining the Time of Year at which Timber was Cut, For. Quarterly, Vol. VIII, 1908. Buckhout, W. A.: The Formation of the Annual Ring of Wood in the Euro- i, pean Larch and the White Pine, For. Quarterly, Vol. V, No. 3, Sept. 1907, pp. 259-267. Dacherowski, A.: Type and Variability in the Annual Wood Increment of Acer rubrum, L. Ohio Nat. 8, pp. 343-349, 1908. Nordlinger, H.: Die Holzringe als Grundlage des Baumkorpers, Stuttgart, 1872. Sanio, Carl: Botanische Zeitung, Vol. XXI, No. 50, 1863, pp. 391-399. Hartig, R.: Lehrbuch der Anatomie und Physiologie der Pflanzen, pp. 261-263. HEARTWOOD AND SAPWOOD The course of development of the various wood elements is fundamentally the same, viz., they are formed in the cambium, they increase in size, their walls thicken more or less, they function as living cells for a time, but eventually lose their protoplasmic contents and die. Their change from a living to a dead condition is ordinarily not followed by immediate decay, and the cells continue to perform the mechanical function of support. The parenchyma cells remain alive for a longer time than the other elements. The outer layers of growth of a tree, especially one of con- siderable thickness, contain the only living elements of the wood and comprise the sapwood. There is usually a sharp line of demarcation between the living elements of the sapwood and the non-living elements of the heartwood, though the vigor of the living cells gradually wanes as their distance from the cambium increases. The thickness of sapwood varies widely in different species, in different individuals, in different portions of a single tree, and often on different radii of any particular section. Thin sapwood is characteristic of certain genera, for example Catalpa, Robinia, Toxylon, Sassafras, Morus, Gymnocladus, Juniperus, and Taxus, while in others such as Hicoria, Acer, Fraxinus, Celtis, and Fagus, thick sapwood is the rule. The fact that sapwood occupies the peripheral layers of the stem causes it to form a considerable proportion of the volume. The percentage of sapwood to total volume of the stem is for certain species approximately as follows: Pinus palustris, 40; ECONOMIC WOODS OF THE UNITED STATES 45 P. heterophylla, 50; P. tceda, 55; P. strobus, 30; Tilia americana, 65; Juniperus virginiana, 25; Liriodendron tulipij 'era, 20; Quercus alba, 20; Robinia pseudacacia, 12. In the same species there generally exists a constant relation between the crown space and the cross-sectional area of the sapwood in the stem. Rapidly growing trees and trees in the open have a larger proportion of sapwood than those of the same species growing in less open stands. In the latter case the number of rings in the sapwood is almost always greater. Heartwood in general is of a darker color than sapwood, due to the presence of gums, resins, and other substances. In some genera, however, there is little difference in appearance between these two portions, for example, in Nyssa, Ilex, Celtis, Populus, Salix, Picea, Abies, and Tsuga. Change from sapwood to heartwood is never accompanied by increased lignification. Deposition of large amounts of gum or resin materially increases the weight of the wood, and on that account in certain tropical species the heartwood averages fully one-third heavier than the sapwood. While physiologically heartwood is that portion of the woody cylinder which does not contain living elements, yet technically only discolored parts are so called, though it of course is without living elements. Branches form heartwood as soon as they cease to grow vigorously, no matter in what part of the crown they are located. In a whorl one branch may be practically all heartwood while none of the others shows any. Usually heartwood is commercially more valuable than sap- wood, partly on account of its color, but more especially because of its greater durability under exposure. In grading lumber sapwood is often considered a defect. Important exceptions are found in the use of paper birch for spools, hickory and ash for handles, spokes, etc., woods for manufacture of pulp, and timber to be impregnated with preservatives, where heartwood is con- sidered undesirable. The average thickness of the sapwood and the character of the demarcation between heartwood and sapwood are features fre- quently made use of in classification. References Roth, F.: Timber, Bui. 10, U. S. Div. of Forestry, p. 13. Boulger, G. S.: Wood, p. 17. 46 ECONOMIC WOODS OF THE UNITED STATES DeBart, A.: Comparative Anatomy, pp. 507-511. Munch, Ernst: Ueber krankhafte Kembildung, Naturw. Zeitschrift fur Forst-und Landwirtschaft, 8. Jahrgang, 1910, pp. 533-547; 553-569. Nordlinger, H.: Die Technischen Eigenschaften der Holzer, Stuttgart, 1860, pp. 28-40. GRAIN AND TEXTURE Grain is a general term used in reference to the arrangement or direction of the wood elements and to the relative width of the growth rings. To have specific meaning it is essential that it be qualified. The kinds of grain commonly described are fine, coarse, even, uneven, rough, smooth, straight, cross, spiral, twisted, wavy, curly, mottled, landscape, bird's-eye, gnarly, and silver. Coarse grain applies to woods of rapid growth, i.e., it denotes wide rings; fine grain, to woods of slow growth. Even and uneven apply respectively to regularity or irregularity of the growth rings; rough and smooth, to the manner in which wood works under tools. Straight grain, as applied to a tree, occurs when the wood ele- ments are parallel to the axis of growth; as applied to a board, when the radial and tangential planes of structure are parallel to its length. Sawn boards or timbers are often cross-grained even when cut from straight-grained logs while straight-grained pieces may be split from spiral-grained trees. The strength of a piece of timber, particularly in bending, rapidly weakens as the plane of its fibres deviates from a direction parallel to its length. On this account split timber is usually stronger than when sawn, a fact made use of in wood-working. For instance, billets for handles and blocks for telegraph-insulator pegs are invariably split. It is not uncommon in any tree, and usual in many cases, for the wood elements to be arranged spirally about the central axis. The spiral may run to the right or left, but the direction is usually fairly constant within a species. Various theories have been advanced to explain the phenomenon of spiral growth or torsion. The one most commonly accepted considers the obliquity of the fibres a method of accommodating the increase in length of the cells after their formation in the cambium. There seems to be ground for suspecting that wind may have an influence on this spiral development. For instance, trees of Larix americana have been observed which, though straight-grained while young, had ECONOMIC WOODS OF THE UNITED STATES 47 developed spirally twisted growth layers after the trees were thirty to forty years old, when, unprotected by associated trees, they were subjected to heavy winds. There is a further possibility that some species have an inherent tendency to develop twisted stems. In any event, when such stems are sawn the lumber is cross-grained and usually unfit for use where strength is required. The extent of the defect depends upon the pitch of the spiral. When the elements interweave and are not constant in one general direction, wood is also said to be cross-grained, though the term spiral grain or interlocked grain is more applicable. Often this condition does not interfere with tangential splitting. Wood with interlocked fibres is tough and not necessarily weakened, but always tends to warp and twist in seasoning. Examples occur in Nyssa, JEsculus, Liquidambar, and Eucalyptus. Wavy grain and curly grain result when the fibres undulate but do not cross each other. When the undulations are large the grain is said to be wavy; when small, curly. Usually the waves are on the radial plane and tangential splitting produces a smooth surface, showing the grain to advantage. Such grain is common in Acer, JEsculus, Fraxinus, Prunus, and Betula. It is most common near the roots and at the insertion of large branches. Silver grain is produced by quarter-sawing timber in which the rays are sufficiently high to show readily on radial surface. The appearance of the rays adds very materially to the value of woods for cabinet work and furniture. Species which exhibit conspicuous silver grain are Quercus (all species, but particularly Q. alba), Platanus occidentalis, Fagus americana, and to a less extent Acer saccharum, Prunus serotina, and Swietenia mahagoni. Texture is a term which refers to the relative size, quality, or fineness of the elements as affecting the structural properties of a wood. Like grain, it requires qualifying adjectives to attain specific meaning. The most common attributes of texture are fineness and coarseness, evenness and unevenness. Coarse texture applies to woods with many large elements, or the average size of which is large, for example, Caslanea, Gymnocladus, Sequoia. In fine texture the opposite condition prevails, as in Juniperus, /Esculus, Salix, Populus. Even texture or uniform texture are terms used to describe woods whose elements exhibit little variation in size, for example, Taxodium (Plate II, Fig. 1), Juniperus (Plate II, Figs. 3, 4), Sequoia, /Esculus (Plate VI, Fig. 5). Uneven texture applies to north r LIBRARY JV. C. State College 48 ECONOMIC WOODS OF THE UNITED STATES the opposite condition, such as is common in all prominently ring-porous woods (Frontispiece; Plate III), (e.g., Quercus, Cas- tanea, Ulmus, Fraxinus), and in other woods with decided differ- ences between early and late wood (e.g., Pinus palustris, P. tceda, and Pseudotsuga). Texture and grain are terms very commonly confused in popular usage. The distinctions as above expressed will obviate the difficulty resulting from the attempt to make the term "grain" too comprehensive. Reference Record, S. J.: Grain and Texture in Wood, Forestry Quarterly, Vol. IX, No. 1, 1911, pp. 22-25 (reprinted in Woodcraft, June 1911). KNOTS Branches originate, as a rule, at the central axis of a stem and, while living, increase in size by the addition from year to year of woody layers which are a continuation of those in the stem. From this it follows that the form of the included portion or knot approaches that of a cone with its apex inward. During the development of a tree most of the limbs, especially the lower ones, die, but persist for a time — often for a great many years. Subsequent layers of growth of the stem are not intimately joined with the fibres of the dead limb, but are laid around its base. Hence dead branches produce loose knots which may drop out after the tree has been cut into lumber. The stubs of dead limbs that have broken off are usually occluded by subsequent growth so that the outer surface of the bole is smooth or clear, especially toward the butt. The interior of all stems is more or less knotty, but in butt logs the knots are fewest and smallest. Sometimes knots enhance the value of timber for cabinet work and interior finish, by giving it a pleasing figure. Material cut near the junction of a large limb or at the base of a crotch usually exhibits very handsome grain. Knots materially affect checking and warping, ease in working, and cleavability of timber. They are defects which weaken timber and depreciate its value for structural purposes where strength is an important consideration. The weakening effect is much more serious where timber is subjected to bending and tension than where under compression. The extent to which a knot affects the strength of a beam depends upon its position, size, direction ECONOMIC WOODS OF THE UNITED STATES 49 of fibre, and condition. A knot on the upper side is compressed, while one on the lower side is subjected to tension. The knot, especially (as is often the case) if there is a season check in it, offers little resistance to tensile stress. Small knots, however, may be so located in a beam as actually to increase its strength by tending to prevent longitudinal shearing. Knots in a board or plank are least injurious when they extend through it at right angles to its broadest surface. Knots apparently have little effect on the stiffness of timber. "At the junction of limb and stem the fibers on the upper and lower sides of the limb behave differently. On the lower side they run from the stem into the limb, forming an uninterrupted strand or tissue and a perfect union. On the upper side the fibers bend aside, are not continuous into the limb, and hence the connection is imperfect. "Owing to the arrangement of the fibers, the cleft made in the splitting never runs into the knot if started on the side above the limb, but is apt to enter the knot if started below, a fact well understood in woodcraft." * Sound knots are as hard as, and usually considerably harder than, the wood surrounding them. In coniferous woods they are commonly highly resinous, and in finished lumber are apt, on that account, to fail to retain paint or varnish. When such trees decay the knots remain sound and are prized for fuel. In grading lumber and structural timber, knots are classified accord- ing to their character (sound, loose, encased), size (pin, standard, large), and direction of fibre (round, spike). References Roth, Filibert: Timber, Bui. 10, U. S. Div. For., 1859, pp. 23, 41, 44 48, 49. Cline, McGarvey, and Knapp, J. B.: Properties and Uses of Douglas Fir, Bui. 88, U. S. Forest Service, 1911, pp. 32-37. DENSITY AND WEIGHT Density of wood varies widely in different species, in different individuals, and even in different portions of the same tree. The specific gravity f of wood substance is about 1.6; hence the * Roth, loc. cit., p. 23. t By specific gravity is meant the ratio of the weight of thoroughly dried 4 50 ECONOMIC WOODS OF THE UNITED STATES reason any wood floats in water is because of the buoyancy of the air imprisoned in its elements and spaces. When this air is dis- placed by water the wood becomes "waterlogged," and will no longer float. The greater the proportion of cell wall the greater the density; consequently late wood is denser and of higher specific gravity than early wood, and the greater the proportion of late wood the denser the wood as a whole. Woods composed largely of thick-walled, narrow-lumined fibres are always dense and heavy. Other things being equal, the weight of wood is a good criterion of its hardness and strength. In practice the weight of wood is calculated from small, sound specimens which have been oven-dried at a temperature of 100° C. (the boiling-point of water) until they reach a constant weight. Since weight is subject to wide variations, the single value usually assigned to a species is really the average of a large number of determinations and is applicable only in a general way. If a wood weighs less than thirty pounds per cubic foot it is con- sidered light; if between thirty and forty pounds, medium light or medium heavy; and if more than forty pounds, heavy. The lightest wood in the United States is that of Leitneria floridana, the specific gravity of which is 0.21 for body wood and 0.15 for root wood. The wood of Condalia ferrea has a specific gravity of 1.3; that of Guaiacum sanctum 1.14. From the inves- tigation of 429 American species, as published in the report of the Tenth Census of the United States, it appears that 242 species, including most of the commercial woods, lie between 0.45 and 0.75 in specific gravity. TABLE III One Hundred and Fifty Trees of the United States Arranged in Order of the Average Specific Gravity of Their Dry Woods (Tenth Census). Species Sp. Gr. Quercus prinoides 86 Quercus chrysolepis 85 Hicoria alba S4 Ostrya virginiana 83 Sp. Gr. Condalia ferrea 1 . 30 Guaiacum sanctum 1 . 14 Quercus virens 95 Quercus texana 91 wood to an equal volume of water at its greatest density, which occurs at a temperature of 4° C. (39.2° F.). A cubic foot of pure water at this temperature weighs 62.43 pounds. Dividing the weight in pounds of a cubic foot of wood by 62.43 will give the specific gravity of the wood. ECONOMIC WOODS OF THE UNITED STATES 51 TABLE Species Sp. Gr. Quercus agrifolia 83 Hicoria glabra 82 Cornus florida 82 Hicoria laciniosa 81 Quercus michauxii 80 Hicoria myristicseformis 80 Pinus serotina 79 Diospyros virginiana 79 Toxylon pomiferum 77 Quercus laurif olia 77 Prosopis juliflora 77 Betula lenta 76 Quercus imbricaria 75 Pinus heterophylla 75 Quercus prinus 75 Ulmus alata 75 Quercus phellos 75 •Quercus alba 75 Quercus macrocarpa 75 Ilex decidua 74 Hicoria aquatica 74 Larix occidentalis 74 Quercus coccinea 74 Robinia pseudacacia 73 Quercus nigra 73 Celtis occidentalis 73 Carpinus caroliniana 73 Swietenia mahagoni 73 Ulmus racemosa 73 Ulmus crassifolia 72 Quercus aquatica 72 Prunus americana 72 Crataegus crus-galli 72 Fraxinus quadrangulata 72 Hicoria olivaef ormis 72 Juniperus monosperma 71 Fraxinus lanceolata 71 Quercus velutina 70 Pinus palustris 70 Ulmus pubescens 70 Quercus palustris 69 Gymnocladus dioicus 69 Acer saccharum 69 Fagus americana 69 Gleditsia triacanthos 67 Betula lutea 66 Fraxinus americana 65 III — Continued Species Sp. Gr. Quercus rubra 65 Ulmus americana 65 Taxus brevif olia 64 Pinus edulis 64 Magnolia grandiflora 64 Nyssa sylvatica 64 Taxus floridana 63 Cupressus macrocarpa 63 Fraxinus pennsylvanica 63 Larix americana 62 Acer rubrum 62 Juglans nigra 61 Pinus echinata 61 Betula papyrif era 60 Liquidambar styraciflua 59 Morus rubra 59 Castanea pumila 59 Juniperus pachyphlcea 58 Prunus serotina 58 Ilex opaca 53 Juniperus occidentalis 58 Betula nigra 58 Betula populifolia 58 Fraxinus oregona 57 Platanus occidentalis 57 Pinus monophylla 57 Castanopsis chrysophylla 56 Pinus aristata 56 Juniperus utahensis 55 Pyrus americana 55 Pinus taeda 54 Pinus balfouriana 54 Magnolia macrophylla 53 Pinus inops 53 Pinus jeffreyi 53 Pseudotsuga taxifolia 52 Pinus rigida 52 Tumion taxifolium 51 Sassafras sassafras 50 Magnolia glauca 50 iEsculus calif ornica 50 Juniperus virginiana 49 Pinus resinosa 49 Alnus oregona 48 Chamsecyparis nootkatensis ... .48 Tumion californicum 48 Pinus ponderosa 47 52 ECONOMIC WOODS OF THE UNITED STATES TABLE III— Continued Species Sp. Gr. Abies magnifica 47 Magnolia acuminata 47 Populus grandidentata 46 Chamsecyparis lawsoniana 46 Picea nigra 46 Abies nobilis 46 Taxodium distichum 45 ^Esculus glabra 45 Tilia americana 45 Castanea dentata 45 Catalpa catalpa 45 Salix nigra 45 Pinus flexilis 44 Acer negundo 43 Picea sitchensis 43 vEsculus octandra 43 Salix discolor 43 Tilia heterophylla 43 Tsuga canadensis 42 Liriodendron tulipif era 42 Abies amabilis 42 Sequoia sempervirens 42 Catalpa speciosa 42 Pinus albicaulis 42 Species Sp. Gr. Pinus coulteri 41 Pinus murrayana 41 Populus heterophylla 41 Juglans cinerea 41 Tilia pubescens 41 Picea alba 41 Populus tremuloides 40 Libocedrus decurrens 40 Asimina triloba 40 Alnus oblongifolia 40 Pinus glabra -39 Pinus monticola 39 Pinus strobus 38 Abies balsamea 38 Populus trichocarpa 38 Thuya plicata 38 Pinus lambertiana 37 Abies concolor 36 Populus balsamifera 36 Abies grandis 35 Picea engelmanni 34 Thuya occidentalis 32 Sequoia washingtoniana 29 I Leitnena floridana 21 References Roth, F.: Timber, Bui. 10, U. S. Div. Forestry, pp. 25-28. Sargent, C. S.: Forests of North America, Part 9, Tenth Census of the U. S., Washington, 1884, pp. 248-251. Gayer, K: Schlich's Manual of Forestry, Vol. V, 1908, pp. 50-65. Nordlinger, H.: Die Technischen Eigenschaften der Holzer, Stuttgart, 1860, pp. 115-227. WATER CONTENT OF WOOD Water occurs in living sap wood in three states, viz., (1) in the protoplasmic contents of the cells, (2) in the cell walls, and (3) as free water wholly or partially filling the iumina of cells, fibres, and vessels that have lost their contents. In heartwood water normally exists only in condition (2). In the fresh sapwood of Pinus strobus, which may be taken as fairly typical, water com- prises about half of the total weight and is distributed approx- ECONOMIC WOODS OF THE UNITED STATES 53 imately as follows: in contents of living cells, 5 per cent; satu- rating cell walls, 35 per cent; free water, 60 per cent. In a living tree the wood nearest the bark contains the most water. If no heartwood is present the decrease toward the pith is gradual; otherwise the change is quite abrupt at the sapwood limit. In Pinus palustris, for example, the weight of the fresh wood within an inch of the bark may be 50 per cent of water; that between one and two inches, only 35 per cent; that of the heartwood, only 20 per cent. The water content of any par- ticular section of a tree depends upon the amount of sapwood, and is therefore greater for the upper than for the lower portions of the stem; greater for limbs than bole; greatest of all in the roots. The water content of wood can readily be determined in the following manner: saw off a thin section of wood; weigh careful- ly on a delicate balance; dry in an oven at a temperature of 100° C. until a constant weight is obtained; reweigh. The difference between the fresh weight and the dry weight is the amount of moisture contained. Computed on a basis of the fresh weight, fresh weight - dry weight Per cent of moisture = — : r-rr X 1UU. fresh weight Thus if the weight of the original block of wood was twice the final weight, there was as much water as wood; in other words, one-half, or 50 per cent, of the original weight was water. The figures in the preceding paragraph are on this basis. Computed on a basis of dry weight, fresh weight - dry weight Per cent of moisture = ^ r-— X 100. dry weight In the problem cited above the loss of moisture was 100 per cent of the dry weight. This method furnishes a constant basis for comparison, while the other varies with every change in moisture degree. Subsequent references to the per cent of moisture will refer to computation on the basis of dry weight. It is impossible to remove absolutely all the water from wood without destroying the wood. Wood is considered thoroughly dried when it ceases to lose weight in a constant temperature of 100° C, though it still retains 2 to 3 per cent of moisture, and if exposed to higher temperature will continue to give up water. Seasoning, which is essentially drying, adds appreciably to the strength, and, in slightly less proportion, to the stiffness of 54 ECONOMIC WOODS OF THE UNITED STATES wood. A piece of green spruce timber, for example, may become four times stronger when thoroughly dried.* This is an extreme case, however, and does not apply to large timbers where check- ing, which always occurs to some extent, may counterbalance partially or even entirely the gain in strength due to drying. In small forms of hardwood material, as implement and carriage stock, and in coniferous timber in some forms, as cross- arms for telegraph poles, thorough and uniform reduction of the moisture content produces a large increase in strength. In fact a comparatively weak wood may, when perfectly dry, be much stronger than a strong wood in a green condition. Consequently tests to determine the mechanical properties of wood must, to be comparable, take into consideration the moisture content of the specimens. By means of a great many tests the relation of the moisture degree to the mechanical properties can be approx- imated and coefficients or correction factors determined by which the strength value at any given water content can be reduced to a standard (usually 12 per cent) or other desired moisture degree. f Loss of water from cell lumina alone does not affect the mechan- ical properties of wood. It is only when the cell walls begin to give up their water that increase in strength, stiffness, hardness, and resilience occur. Conversely, the absorption of water weakens wood only to the point where the cell walls become completely saturated. This critical point has been termed by Tiemann (loc. cit.) the fibre-saturation point. It varies with different treat- ments of the wood and under different conditions. The water content at this point is greater in wood previously dried and especially in wood which has been subjected to high temperature than it is in green wood. The amount of moisture at the fibre- saturation point in green wood of various species has been found by Tiemann (loc. cit.) to be between 20 and 30 (average about 27) per cent. The water content of wood materially affects durability. Since decay is produced by fungi, and to a less extent by bacteria, both of which require considerable water for their development, * In comparing the strength and stiffness of wood in green and dry condi- tions, the fact should be borne in mind that, owing to shrinkage, dry wood is more compact and contains a greater amount of wood substance per unit of volume than green wood. t Such tables have been prepared for several of the commercial woods of the United States. (See Bui. 70 and Cir. 108, U. S. Forest Service.) ECONOMIC WOODS OF THE UNITED STATES 55 all that is necessary to render even the most perishable wood indefinitely immune from decay is to keep it dry. Wood con- taining not more than 10 per cent of moisture will not decay. Rate of seasoning differs with the kind of wood and with its shape. A thin piece dries more rapidly than a thicker one; sap wood more rapidly than heartwood; a light, open wood more readily than one that is dense and heavy. Large beams or logs are exceedingly slow in drying, requiring from two to several years' seasoning in the open air before reaching an air-dry condi- tion in the interior. Ties require from three months to a year to season, depending on the kind of timber and the climate. Much depends upon the method of piling, since boards in open piles often dry twice as fast as those in solid piles. As a result of numerous experiments by the U. S. Forest Service upon large beams of Pinus palustris and P. toeda, the following conclusions were reached (Bui. 70, p. 123) : " (1) The drying-out process takes place almost wholly through the faces of the beam and not longitudinally, except near the ends. " (2) The ratio of evaporation through a surface is proportional to the rate of growth or density of the wood near the surface, being most rapid in the case of sap wood. " (3) If the whole stick is made up of heartwood or the pro- portion of sapwood is uniform throughout, the longitudinal dis- tribution of moisture is very regular. If the proportion of sap- wood is not uniform, on the other hand, the portion containing the most sap is the most susceptible to moisture influences; i.e., it will dry or will absorb moisture the most rapidly. "The average of two cross-sections of longleaf pine sticks, 12 by 12 inches and 8 by 16 inches and 16 feet long, which were air-dried for two years, showed an average moisture content in the outer portion, cut halfway from surface to centre, of 17.7 per cent, while the inner part contained 25.7 per cent. "From this it is quite evident that where timber of structural sizes is used, the strength ordinarily reckoned upon should not be greater than that of the green condition." References Roth, F.: Timber, Bui. 10, U. S. Div. Forestry, pp. 29-31. Tiemann, H. D.: The Effect of Moisture upon the Strength and Stiffness of Wood, Bui. 70, U. S. Forest Service, 1906, p. 144. 5(5 ECONOMIC WOODS OF THE UNITED STATES Tiemann, H. D.: The Strength of Wood as Influenced by Moisture, Cir cular 108, U. S. Forest Service, 1907, p. 42. Johnson, J. B.: Timber Physics, Part II, Bui. 8, U. S. Div. of Forestry 1893, pp. 22-24. SHRINKAGE, WARPING, AND CHECKING The volume of wood is maximum when the cell walls are saturated with water. When this condition exists the presence or absence of free water in the cell cavities and the intercellular spaces does not affect the volume. When the cell walls begin to dry, they become thinner, but do not contract to an appreciable extent longitudinally. A dry wood cell is therefore of practically the same length as it was in a green or saturated condition, but is smaller in cross section, has thinner walls and a larger lumen. According to Nageli's hypothesis, the cell wall is composed of aggregations in crystalline form of minute parts or micellae,. These micellce are separated by films of water which become thinner as the wall dries and thicker as it swells. This shrinkage is roughly proportional to the thickness of the walls, and in con- sequence the denser woods or the denser portions of a wood shrink more than those less dense. Inasmuch as wood is not a homogeneous substance, but an intricate structure composed of cells exhibiting from moderate to extreme variation in shape, size, thickness of walls, and more, especially in arrangement, it follows that shrinkage cannot be uniform throughout any specimen. Late wood, being denser, shrinks more than early wood. The ray cells, with their longest diameters for the most part at right angles to the direction of the other elements, oppose radial shrinkage and tend to produce longitudinal shrinkage of wood. Only in the tangential direc- tion are these otherwise opposing forces parallel. For this reason as well as the fact that the denser bands of late wood are tangentially continuous, while radially they are separated by alternate zones of less dense early wood, wood usually shrinks more than twice as much tangentially as it does radially. In all cases, however, shrinkage parallel to the vertical axis is very slight, one-tenth to one-third of one per cent, and is maximum in woods with curly or wavy grain or with large or very abundant rays. The following table gives the results of a series of shrinkage- ECONOMIC WOODS OF THE UNITED STATES 57 tests made by Mr. Hugh P. Baker at the Yale Forest School. The figures given represent the average shrinkage resulting from reducing green wood to a kiln-dry condition and are com- puted on the basis of the original measurements. TABLE IV Shrinkage of Wood along Different Dimensions Species. Length % Radius % Diameter Circum- ference % Area of cross section % Volume % Juniperus virginiana Castanea dentata 0.32 .25 .24 .04 .36 .15 .10 2.7 3.0 3.7 7.4 2.9 4.3 6.1 2.5 3.2 3.5 7.5 3.1 4.8 6.2 5.6 4.9 8.2 9.2 6.9 9.3 11.5 6.9 11.2 10.4 19.4 7.3 12.6 17.1 5.9 19.8 7.6 13.7 1S.0 Liriodendron tulipifera. . . Nyssa sylvat ica Irregularities in shrinkage tend to cause wood to become distorted or warped. In woods with straight grain and uniform texture the tendency to warp is minimum unless the distribution of the moisture content is very unequal. Thus the upper surface of a green board exposed to the hot rays of the sun will dry much more rapidly, and therefore becomes shorter than the lower side, causing the board to curl up at the ends. Woods with interlaced fibres or with cross or spiral grain {e.g., Nyssa, Liquidambar, Eucalyptus) always shrink unequally, and consequently require careful handling in drying to prevent serious deformation. Warp- ing clue to unequal distribution of moisture may subsequently be overcome by thorough drying, but the deformation resulting from great irregularity of structure is usually permanent. In Fig. 15 is shown in somewhat exaggerated manner the deformation caused by the greater tangential shrinkage. The flat side of a log cut through the middle becomes convex (B). Boards cut from half of a log assume the form shown in (C), while a plank from the middle of a log becomes convex on both sides. This explains most of the difference in shrinkage of timbers and boards of different sizes, shapes, and manner of sawing (i.e., whether plain or quarter-sawed). When the strains due to unequal shrinkage can no longer 58 ECONOMIC WOODS OF THE UNITED STATES be accommodated by the plasticity of the wood substance, cracks or checks are formed. These are most common along the rays, since there the strains are greatest and most complex. However, when the strength of the rays is greater than the cohesive force 1910. Elliott, S. B. : The Important Timber Trees of the United States. Boston and New York, Houghton Mifflin Co., 1912. Gibson, Henry H., and Maxwell, Hu: American Forest Trees. Chicago, Hardwood Record, 1913. Hough, Franklin B.: The Elements of Forestry. Cincinnati, The Robert Clarke Co., 1898. Hough, Romeyn B.: American Woods (Sections and Text). Vols. 1-13, Lowville, N. Y., the author, 1893-1913. Hough, Romeyn B.: Handbook of the Trees of the Northern States and Canada East of the Rocky Mountains. Lowville, N. Y., the author, 1907. Koehler, Arthur: Guidebook for the Identification of Woods used for Ties and Timbers. U. S. Forest Service, Washington, D. C, 1917. Jepson, Willis L.: The Silva of California (Vol. II, Memoirs of the Uni- versity of California). Berkeley, University Press, 1910. Lazenby, William R.: Qualities and Uses of the Woods of Ohio. Bui. 6, Ohio Biol. Survey. Columbus, O., 1916. Lee, H. N.: Canadian Woods for Structural Timbers. Dept. of Int., Canada. Forestry Branch, Bid. No. 59, Ottawa, 1917. Levison, J. J. : Studies of Trees. New York, John Wiley & Sons, Inc., 1914. Mohr, Charles, and Roth, Filibert: The Timber Pines of the Southern United States, together with a Discussion of the Structure of their Wood. Bui. 13 (rev. ed.) U. S. Div. Forestry, Washington, D. C, 1897. Newlin, J. A., and Wilson, Thomas R. C: Mechanical Properties of Woods Grown in the United States. Bui. No. 556, U. S. Dept. Agr., Wash- ington, D. C, 1917. Noyes, William: Wood and Forest (2d ed.). The Manual Arts Press, Peoria, 111., 1911. Pexhallow, David P.: A Manual of the North "American Gymnosperms, exclusive of the Cycadales, but together with Certain Exotic Species. Boston, Ginn & Co., 1907. Pinchot, Gifford, and Ashe, W. W. : Timber Trees and Forests of North Carolina. Bui. 6, N. C. Geol. Survey, Chapel Hill, N. C, 1897. Prichard, R. P. : The Structure of the Common Woods of New York and the Wood Collection. Bui. N. Y. State College of Forestry, Syracuse, N. Y., March 1915. Rattinger, K. K.: Die Nutzholzer der Vereinigten Staaten; I. Die Nadel- holzer. Wiesbaden, Verlag Forstburo, 1910. Record, Samuel J.: The Mechanical Properties of Wood. New York, John Wiley & Sons, Inc., 1914. Roth, Filibert: Timber: An Elementary Discussion of the Characteristics and Properties of Woods. Bui. No. 10, U. S. Div. of Forestry, Washington, D. C, 1895. 122 ECONOMIC WOODS OF THE UNITED STATES Sargent, Chas. S. : Report on the Forests of North America (exclusive of Mexico). Vol. 9, Tenth Census, Washington, D. C, 1884. Sargent, Chas. S. : The Woods of the United States, with an Account of the Structure, Qualities and Uses (Jesup Collection). New York, D. Appleton A Co., 1885. 1 Sargent, Chas. S.: The Silva of North America: A Description of the Trees which Grow Naturally in North America, exclusive of Mexico. Vols. 1-14. Boston and New York, Houghton Mifflin Co., 1891-1902. Sargent, Chas. S.: Manual of the Trees of North America (exclusive of Mexico). Boston and New York, Houghton Mifflin Co., 1905. Shinn, Charles H. : Economic Possibilities of Pinus sabiniana. Proc. Soc. Am. Foresters, 6: 1: 68-77, 1911. Snow, Charles H.: The Principal Species of Wood (2d ed.). New York, John Wiley & Sons, Inc., 1908. Snow, Charles H.: Wood and Other Organic Structural Materials. New York, McGraw-Hill Book Co., 1917. Southern Yellow Pine Timbers. Including Definition of the New "Density" Rule. Adopted and copyrighted by the American Society for Testing Materials. Approved and adopted by the Southern Pine Association of New Orleans, La., Nov. 1915. Sterrett, W. D. : Scrub Pine. Bui. 94, U. S. Forest Service, Washington, D. C, 1911. Sudworth, George B.: Forest Trees of the Pacific Slope. U. S. Forest Service, Washington, D. C, 1908. Sudworth, George B.: Miscellaneous Conifers of the Rocky Mountain Region. Bui. No. 680, U. S. Dept. Agr., Washington, D. C, 1918. Sudworth, George B.: The Pine Trees of the Rocky Mountain Region. Bui. No. 460, U. S. Dept. Agr., Washington, D. C, 1917. Sudworth, George B., and Mell, Clayton D.: The Identification of Important North American Oak Woods, based on a Study of the Secondary Wood. Bui. 102, U. S. Forest Service, Washington, D. C, 1911. Sudworth, George B., and Mell, Clayton, D.: Distinguishing Char- acteristics of North American Gumwoods, based on the Anatomy of the Secondary Wood. Bui. 103, U. S. Forest Service, Washington, D. C, 1911. Sudworth, George B., and Mell, Clayton D.: Identification of North American Walnut Woods. Hardwood Record, Chicago, Sept. 10 and 25, 1914. Thelen, Rolf: The Structural Timbers of the Pacific Coast. Proc. Am. Soc. Test Mat., 8: 558-567, 1908. Zon, Raphael: Balsam Fir. Bui. No. 55, U. S. Dept. Agr., Washington, D. C, 1914. 2. Uses of Woods; Wood-using Industries Armstrong, Andrew K.: Wood-using Industries of California. Bui. No. 3, Cal. State Board of Forestry, Sacramento, 1912. Betts, H. S.: Properties and Uses of the Southern Pines. Cir. 164, U. S. Forest Service, Washington, D. C.,*1909. ECONOMIC WOODS OF THE UNITED STATES 123 Brooks, A. B.: Wood Manufacturing Industries of West Virginia. Vol. 5, Chap. 9, pp.'_430-461, West Virginia Geological Survey, Morgantown, W. Va., 1910. Brush, W. D.: Utilization of Elm. Bui. No. 683, U. S. Dept. Agr., Wash- ington, D. C, 1918. Cline, McGarvey, and Knapp, J. B.: Properties and Uses of Douglas Fir. Bui. 38, U. S. Forest Service, Washington, D. C, 1911. Dodge, Charles Richards: A Descriptive Catalogue of Manufactures from Native Woods, as Shown in the Exhibit of the U. S. Dept. of Agr. at the World's Industrial and Cotton Exposition at New Orleans, La. Special Re- port No. 10, U. S. Dept. Agr., Washington, D. C, 1886. Dunning, C. W. : The Wood-using Industries of Idaho. Reprint, Pacific Lumber Trade Journal, Seattle, Wash., July 1912. Dunning, C. W.: Wood-using Industries of Ohio. Pub. by Ohio Agr. Exp. Sta., Wooster, O., 1912. Gould, C. W., and Maxwell, Hu: The Wood-using Industries of Missis- sippi. Reprint, Lumber Trade Journal, New Orleans, La., March 15, 1912, pp. 19-29. Gould, Clark W., and Maxwell, Hu: The Wood-using Industries of Tennessee. Reprint, The Southern Lumberman, Nashville, Tenn., May 25, 1912. Hall, William L., and Maxwell, Hu: Uses of Commercial Woods of the United States: I. Cedars, Cypresses, and Sequoias. Bui. 95, U. S. Forest Service, Washington, D. C., 1911. Hall, William L., and Maxwell, Hu: Uses of Commercial Woods of the United States: II. Pines. Bui. 99, U. S. Forest Service, Washington, D. C, 1911. Harris, John T., and Maxwell, Hu: The Wood-using Industries of Alabama. Reprint Lumber Trade Journal, New Orleans, La., May 1, 1912. Harris, J. T., Maxwell, Hu, and Kiefer, Francis: Wood-using In- dustries and National Forests of Arkansas. Bui. 106, U. S. Forest Service, Washington, D. C, 1912. Harris, John T.: Wood-using Industries of New York. Series 14, No. 2, N. Y. State College of Forestry, Syracuse, N. Y., 1913. Hatch, Charles F.: Manufacture and Utilization of Hickory, 1911. Cir. 187, U. S. Forest Service, Washington, D. C, 1911. Hatch, Charles F., and Maxwell, Hu: The Wood-using Industries of Missouri. Reprint, St. Louis Lumberman, St. Louis, Mo., March 15, 1912,, pp. 68-82. Hoffman, B. E. : Alaska Woods, Their Present and Prospective Uses. For. Quarterly, 11: 2: 185-200, June 1913. Kellogg, R. S.: Lumber and Its Uses. Chicago, Radford Architectural Co., 1914. Knapp, Joseph Burke: Montana's Secondary Wood-using Industries. Reprint, The Timberman, Portland, Ore., Nov. 1912. Lamb, G. N.: Farm Woodlot Timber: Its Uses and Principal Markets. Bui. No. 51, Dept. of Agr. Extension, Purdue University, LaFayette, Ind., 1916. 124 ECONOMIC WOODS OF THE UNITED STATES Lamb, George N.: Willows: Their Growth, Use, and Importance. Bui. No. 316, U. S. Forest Service, Washington, D. C., 1915. Lazenby, William R. : The Economic Uses of Wood. Pub. by Ohio State University, Columbus, O., 1904. Lazenby, William R. : Qualities and Uses of the Woods of Ohio. Vol. 20, No. 9, Ohio State University. Bui. 6, Vol. 2, No. 2, Ohio Biol. Survey, 1916. Lee, H. N.: Canadian Woods for Structural Timbers. Bui. No. 59, Forestry Branch, Dept. Int. Canada, Ottawa, 1917. Lewis, R. G., and Boyce, W. Guy H.: Wood-using Industries of the Maritime Provinces. Bui. No. 44, Forestry Branch, Dept. of Int. Canada, Ottawa, 1914. Lewis, R. G., and Boyce, W. Guy H.: Wood-using Industries of Ontario. Bui. No. 36, Forestry Branch, Dept. Int. Canada, Ottawa, 1913. Lewis, R. G., and Boyce, W. Guy H.: Wood-using Industries of the Prairie Provinces. Bui. No. 50, Forestry Branch, Dept. Int. Canada, Ottawa, 1915. Lewis, R. G., and Doucet, J. A.: Wood-using Industries of Quebec. Bui. No. 63, Forestry Branch, Dept. Int. Canada, Ottawa, 1918. MacMillan, H. R.: Wood-using Industries, 1910. Bui. No. 24, Forestry Branch, Dept. Int. Canada, Ottawa, 1912. Mason, D. T.: Utilization and Management of Lodgepole Pine in the Rocky Mountains. Bui. No. 234, U. S. Forest Service, Washington, D. C, 1915. Maxwell, Hu: Uses of Commercial Woods of the United States: Beech, Birches, and Maples. Bui. No. 12, U. S. Forest Service, Washington, D. C, 1913. Maxwell, Hu: The Uses of Wood. American Forestry, 24:293-300, May to Dec. 1918. Maxwell, Hu: Utilization of Osage Orange. Pub. by Farm Wagon Dept., Natl Implement and Vehicle Ass'n., U. S. A., 1911. Maxwell, Hu: Wood-using Industries of Florida. Pub. by Fla. Dept. of Agr., Talahassee, 1912. Maxwell, Hu : The Wood-using Industries of Louisiana. Reprint, Lumber Trade Journal, New Orleans, La., Jan. 1, 1912. Maxwell, Hu: The Wood-using Industries of Maryland. Bui. Maryland State Board of Forestry, Baltimore, Md., 1910. Maxwell, Hu: A Study of the Massachusetts Wood-using Industries. Pub. by State of Mass., Boston, 1910. Maxwell, Hu: Wood-using Industries of Michigan. Pub. by Public Domain Commission, Lansing, Mich., 1912. Maxwell, Hu, and Harris, John T. : The Wood-using Industries of Iowa. Pub. by Agr. Exp. Sta., Iowa State College of Agr. and Mechanic Arts, Ames, Iowa, 1913. Maxwell, Hu, and Harris, John T. : Wood-using Industries of Vermont. Forestry Pub. No. 11, Dept. of Agr. and Forestry of the State of Vt., Rutland, Vt., 1913. ECONOMIC WOODS OF THE UNITED STATES 125 Maxwell, Hu, and Harris, John T. : Wood-using Industries of Minnesota. Pub. by Minn. State Forestry Board, St. Paul, Minn., 1913. Maxwell, Hu, and Hatch, Charles F. : The Wood-using Industries of Texas. Reprint, Lumber Trade Journal, New Orleans, La., June 15, 1912. Nellis, J. C. : The Wood-using Industries of Indiana. Reprint, Hardwood Record, Chicago, 111., March 1, 1916. Nellis, J. C: The Wood-using Industries of Maine. Report Forest Com- missioner, Waterville, Me., 1912. Nellis, J. C. : Lumber Used in the Manufacture of Wooden Products. Bui. No. 605, U. S. Dept. Agr., Washington, D. C, 1918. Nellis, J. C, and Harris, J. T.: Wood-using Industries of West Virginia. Bui. No. 10, W. Va. Dept. of Agr., Charleston, W. Va., 1915. Oakleaf, Howard B.: Wood-using Industries of Oregon, with Special Re- ference to the Properties and Uses of Oregon Woods. Pub. by Ore. Conserva- tion Ass'n., Portland, Ore., 1911. Oakleaf, Howard B.: Washington's Secondary Wood-using Industries. Pacific Lumber Trade Journal, Seattle, Wash., 1911. Pierson, Albert H.: Wood-using Industries of Connecticut. For. Pub. No. 7, Bui. 174, Conn. Agr. Exp. Sta., New Haven, Conn., Jan. 1913. Pierson, Albert H.: Wood-using Industries of New Jersey. Pub. by Forest Park Reservation Com. of New Jersey, Union Hill, N. J., 1914. Pratt, Merritt B.: The Use of Lumber on California Farms. Bui. No. 299, Agr. Exp. Sta., Berkeley, Cal., 1918. Simmons, Roger E.: The Wood-using Industries of Illinois. Pub. by Uni- versity of Illinois, Urbana, 111., 1911. Simmons, Roger E.: A Study of the Wood-using Industries of Kentucky. Pub. by Dept. Agri., Labor and Statistics, Frankfort, Ky., 1910. Simmons, Roger E.: Wood-using Industries of New Hampshire. Pub. by State of N. H. Forestry Com., Concord, N. H., 1912. Simmons, Roger E.: Wood-using Industries of North Carolina. Econ. Paper No. XX, N. C. Econ. and Geol. Survey, Raleigh, N. C, 1910. Simmons, Roger E. : Wood-using Industries of Pennsylvania. Bui. No. 9, Dept. of Forestry, Harrisburg, Pa., April, 1914. Simmons, Roger E.: Wood-using Industries of Virginia. Pub. by Dept. of Agr. and Immigration, Richmond, Va., 1912. Smith, Franklin H. : A Study of the Wisconsin Wood-using Industries. Pub. by Forestry Dept., Madison, Wis., 1910. Surface, G. T.: The Commercial Woods of the United States and Their Uses. Reprint, Bui. Geog. Soc. of Phila., Vol. VIII, No. 3, July 1910. Swan, O. T.: The Wood-using Industries of Georgia. Reprint, Lumber Trade Journal, New Orleans, La., Mar. 15, 1915. Wolfe, Stanley L.: Wood-using Industries, of South Carolina. Pub. by Dept. of Agr., Commerce and Industries, Columbia, S. C., 1913. APPENDIX The Woods of the United States Wood of economic importance is obtained from certain repre- sentatives of the highest sub-division of the plant world — the Spermatophytes or true flowering and seed-bearing plants. Bot- anists separate this large group, chiefly on the basis of floral and fruit characters, into two classes, viz., the Gymnosperms and the Angiosperms. The Gymnosperms are all woody plants, either trees or shrubs. Of the fifteen genera indigenous to the United States, two (Taxus and Tumion or Torreya) belong to the Taxaceae or yew family and are of little or no commercial importance. The other thirteen belong to the Coniferse or true cone-bearers. The woods of the Coniferse, commonly known as coniferous woods or softwoods, are esteemed for structural purposes because they combine a high degree of strength and stiffness with com- paratively light weight and ease of manipulation. They are separable into (a) the pine-like and (b) the cedar-like. The first includes the pines (Pinus), Douglas fir (Pseudotsuga) , spruces (Picea), larches (Larix), true firs (Abies), and the hemlocks (Tsuga). The second group embraces the junipers (Juniperus), various cedars (Chamcecy parts, Thuya, Libocedrus) , the cypresses (Cupres- sus and Taxodium), and the sequoias (Sequoia). The cedar-like woods are characterized by their resistance to decay and also, with the exception of Taxodium and Sequoia, by their fragrant scent. The Angiosperms are very abundantly represented in the flora of this country and include a large proportion of herbaceous forms. Two sub-classes are recognized, viz., the Monocotyledons and the Dicotyledons, referring to the number of cotyledons or seed-leaves of the embryo. There are also fundamental differences in their stem structures. Monocotyledonous stems are mostly unbranched and the wood is confined to isolated strands disposed irregularly in a mass of softer tissue, becoming more and more compact toward the surface. In general, there are lacking certain important features which characterize the stems of both Gymnosperms and Dicotyledons, 127 128 ECONOMIC WOODS OF THE UNITED STATES viz., (a) a distinct central core of pith, (b) a covering of bark, and between these two (c) a fairly uniform mass of wood which in- creases in thickness by the addition of periodic layers on the outside. Some well-known representatives of the Monocotyledons are the grasses (including maize, wheat, many other cereals, the bam- boos, etc.), the sedges, lilies, bananas, rattans, palms, and yuccas. The woody types are confined chiefly to tropical and sub-tropical regions where they are extensively used but not in the form of lumber. There are seven kinds of palms and nine kinds of yuccas of tree size native to the United States. They are used to some extent locally but as a commercial source of wood are wholly negligible. As stated on p. 7 there are, according to Sargent's " Manual of the Trees of North America," 62 families and 162 genera of Dico- tyledons with representatives of tree size in this country. The total number of species described is 618. Various others have been introduced, mostly for decorative purposes but also to a small extent for forest planting, and a few have become naturalized, but only in rare instances do their woods contribute to our commercial supply. Sud worth's " Check List " * enumerates 495 trees, includ- ing a few which have become thoroughly naturalized. This dis- crepancy is accounted for mostly by the large number of species of Crataegus, 153 in all, described by Sargent as against 25 listed by Sudworth. Not a single representative of this genus is of commer- cial importance for its wood, and of the 45 species belonging to the other genera of the Rosacese only one, Prunus serotina, is a source of valuable lumber. One willow out of 24 species, about 22 oaks out of a total of 54, and about a dozen pines out of the 28 native to this country are commercially valuable. In the Govern- ment reports on lumber production only 30 kinds are considered of sufficient importance to justify separate tabulation, while about 20 are grouped under the single heading of "minor species." The following list includes the most important families and genera of the Dicotyledons. Included in it are seven families which are really of secondary importance so far as the amount of the wood produced is concerned. These are, Aquifoliacese, Bignoniacese, Ebenaceae, Hippocastanacese, Lauracess, Meliacese, and Moracese. (Cornacese includes Nyssacese of Sargent.) * Sudworth, George B.: Check last of the Forest Trees of the United States, Their Names and Ranges. Bui. No. 17, U. S. Division of Forestry, Washington, D. C, 1898. ECONOMIC WOODS OF THE UNITED STATES 129 TABLE V Important Families and Genera of Dicotyledons in the United States Aceraceoe Acer (maple) Aquifoliacece Ilex (holly) Betulacece Alnus (alder) Betula (birch) Bignoniacece Catalpa (catalpa) Cornacece Cornus (dogwood) Nyssa (tupelo) Ebenacece Diospyros (persimmon; Fagacece Castanea (chestnut) Castanopsis (chinquapin) Fagus (beech) Quercus (oak) Hamamelidacece Liquidamabar (red gum) Hippo castanacecB iEsculus (buckeye) J uglandacecB Hicoria (hickory) Juglans (walnut) Lauracece Sassafras (sassafras) Leguminosce Gleditsia (honey locust) Gymnocladus (Ky. coffee-tree) Robinia (black locust) Prosopis (mesquite) Magnoliacece Liriodendron (tulip-tree) Magnolia (magnolia; cucumber) Meliacece Swietenia (mahogany) Moraceoe Morus (mulberry) Toxylon (Osage orange) Oleaceaz Fraxinus (ash) Platanacece Platanus (sycamore) Rosacea? Prunus (black cherry) Salicacece Populus (poplar; cottonwood) Salix (willow) Tiliaceos Tilia (basswood) Ulmacece Celtis (hackberry) Ulmus (elm) TABLE VI Numerical Conspectus of the Trees of the United States Class Number of Families Number of Genera Number of Species Number of Economic Species which can be iden- Total Economic Total Economic Total Economic tified from the Wood alone Gymnosperms 2 1 15 12 84 37 25-30 CO 2 Monocotyledons 2 8 21 CO O "So a < Dicotyledons 62 22 162 40 618 100 55-65 Totals 66 23 185 52 723 137 80-95 130 ECONOMIC WOODS OF THE UNITED STATES WOOD STRUCTURE Wood is a fibrous structure composed of cells which are for the most part greatly elongated in a vertical or axial direction. Longi- tudinal surfaces accordingly show the fibrous nature of wood to the best advantage, while the cross section appears under the micro- scope more or less like a fine honey-comb. Some wood cells are large enough to be readily seen, others are at the limit of vision and require a hand lens for distinctness, and a much larger number are not individually visible without considerable magnification. All wood cells when first formed contain living protoplasm but a large proportion of them apparently lose it very early. Such cells provide channels for sap-flow from root to leaf, lend strength and rigidity to the stem, and in some instances supply spaces for storage of excess food and reservoirs for waste products. Since these functions are in part physiological it seems unlikely that the protoplasm has entirely disappeared from the elements concerned, even if its presence cannot be directly demonstrated, since cells without living protoplasm can only function mechanically. The wood cells which obviously retain living protoplasm throughout their functional period may be referred to as food cells (parenchyma) since they are primarily concerned with the dis- tribution and storage of plant food. This food is elaborated in the leaves (and other green tissues) and is transported along the stem chiefly through certain channels (sieve-tubes of the phloem) in the inner bark. The cells (ray parenchyma) which divert por- tions of the food current into the wood are typically elongated in a horizontal or radial direction, while those (wood parenchyma) which distribute it vertically in the stem are axially elongated. Plant food assumes various forms, the principal ones being starch, sugars and fats; the change from one form to another is brought about by the action of certain ferments or enzymes. Structurally, a wood cell consists of a cell wall of ligno-cellulose, inclosing a lumen or cavity (with or without visible contents), and completely surrounded by a pectic layer called the middle lamella. The lignified wall provides a strong and rigid framework. The middle lamella limits the individual cells and cements them firmly together to form the wood-mass. The cavity serves various pur- poses such as the transportation of food and water, aeration, storage, etc., and must accordingly be in communication with the ECONOMIC WOODS OF THE UNITED STATES 131 cavities of adjacent cells and in some instances with intercellular spaces also. Where the cell walls are thin enough there is no need for special provision for intercommunication. The process of thickening reduces the permeability of the walls and makes necessary the leaving of thin or unthickened spots called pits. Were the wall uniformly thickened throughout, the lumen would become isolated and the function of the cell would be reduced to that of reinforce- ment only, a condition approximated in the libriform fibres of certain woods such as Toxylon and Robinia. At the other ex- treme, there are elements (vessels) concerned with the rapid con- duction of water which are composed of vertical series of cells whose pits at the ends have given place to true openings or per- forations. The only fundamental difference between a perforation and a pit is that in a pit the middle lamella, somewhat modified, forms a limiting or pit membrane. The presence of minute per- forations in this membrane can be demonstrated by passing finely divided solid particles through it. Some cells have simple pits while others appear under the compound microscope to have a more or less distinct border. This border is due to the wall overhanging the margin of the pit membrane. Pits between food-cells are simple while those be- tween water-carriers are bordered. Where the two types of cells are in communication the half of the pit in the food-cell is always simple and the corresponding portion in the other may be either simple or bordered. In the latter case the pit is structurally half- bordered, though in surface view it may not be distinguishable from one that is bordered on both sides. Pits exhibit a wide range of variation in size, shape and arrangement, and possess high value for purposes of classification of woods. (For further details see pp. 31-35.) CLASSIFICATION OF THE ELEMENTS OF SECONDARY WOOD On p. 13 the cellular elements of wood are referred to three principal types, viz., vascular, fibrous and parenchymatous. Some authors prefer the following classification: (a) vessels (cell- fusions serving for the conduction of water) ; (6) parenchyma (food cells which conduct and store carbohydrates); (c) prosenchyma (cells serving chiefly to give mechanical support but often partici- pating in functions of the other groups). The prosenchyma in- 132 ECONOMIC WOODS OF THE UNITED STATES eludes all of the vertical elements of the wood except vessels and parenchyma, namely, libriform fibres, septate fibres, intermediate or substitute fibres, fibre-tracheids, and tracheids. Libriform fibres are the cells referred to on p. 18 as typical wood fibres. Fibre-tracheids are fibrous cells with distinctly bordered pits and are intermediate between libriform fibres and vessel-like tracheids; they do not occur in Gymnosperms though the tracheids of the late wood might with some justification be so-called. The following diagram shows the relationships of the various elements. In this the tracheid appears as the dominant element. Vessels are composed of segments which were originally tracheids before fusion; intermediate forms occur. Fibre-tracheids and libriform fibres may be considered as modifications of the tracheid in which the mechanical function of strength is emphasized at the expense of water conduction. Intermediate forms between these cells and parenchyma are shown in the diagram which were not brought out in the other classifications. Epithelial cells of resin ducts are shown as specialized forms of parenchyma. TRACHEIDS- Fibre-tyuheids t— Ray tracheids _ ' Substitute fibres ' " I Septate fibres , Ray parenchyma 1 \ 1 ^> E P Wood'parenchyma thelial cells Librifo m fibres VESSELS Vessels are compound elements; they are composed of segments which have become fused at the ends (and sometimes at the sides as well) into vertical series. Each segment normally arises from a single cambial cell and when first formed is completely inclosed by the middle lamella and is morphologically a tracheid. After fusion the cells function, not as a series of individuals, but as a continuous tube. The segments may abut on each other squarely at the ends or overlap more or less. Both forms may occur in the same vessel, though decidedly elongated tips are characteristic of certain species. Such tips are usually provided with bordered pits and in some instances exhibit spiral thickenings even though the body of ECONOMIC WOODS OF THE UNITED STATES 133 the segment does not. Sometimes segments are fused through their lateral walls, or the end of one segment may be joined to the lateral wall of another, but such forms are to be considered ex- ceptional. The plane of contact between segments may be : (a) horizontal or transverse, that is, at right angles to the axis of the vessel; (6) oblique or inclined, almost always facing the ray; (c) vertical or longitudinal. The last may be considered an extreme form of the oblique unless it occurs where segments are fused through their lateral walls. VESSEL PERFORATIONS The opening from one segment into another is called the vessel perforation. The various types and modifications of vessel per- forations supply features highly important for diagnostic purposes. The two principal forms are : (a) the simple and (6) the scalariform. Insofar as our commercial woods are concerned knowledge of these two types is sufficient. There are various other forms, however, though most of them are modifications or malformations of the two principal types. The reticulate form is not uncommon, especially in the Rosacea?, and tendency to it is seen in the branch- ing and anastomosing bars in almost all woods with scalariform perforations. In Rosa sp. the author has observed in a single section, simple (predominating), scalariform, reticulate, pit- perforate, and various composite perforations. The following classification shows the range of variation in perforations, though there are innumerable forms of the composite. A few instances, mostly exotics, are cited as illustrations of the rarer kinds. TYPES OF VESSEL PERFORATIONS Simple: (Single opening, circular, elliptical or elongated-elliptical.) Scalariform: (Openings slit-like or elongated between cross bars.) Bars transverse (Common form). Bars vertical (Very rare. In certain Composite and Axyris amarantoides) . Reticulate: (Irregular openings as meshes between anastomosing bars.) 134 ECONOMIC WOODS OF THE UNITED STATES Multiperforate : (Plural circular or elliptical openings.) Few comparatively large openings (Ephedra; occasionally in Vaccinium uliginosum and Leitneria floridana) . Numerous small openings (Canella alba; Menziesia ferruginea) . Pit-perforate: (Not readily distinguishable from pits.) (Oc- casionally in Meisteria cernua, Lithospermum fruiticosum, Cheirodendron sp., Rosa sp.) Composite: (Mostly malformations occasionally met with.) Simple-scalariform : (Quillaja, certain Bignoniacese, etc.) Simple-reticulate: (Sorbus aucuparia, Sidonia vulgaris, Rosa sp., Cheirodendron gaudichaudii, etc.) Scalariform-reticulate : (Didymopanax morototoni.) Simple perforations characterize a large majority of our native woods. Where the plane of perforation is transverse or only slightly inclined the simple type is almost invariably found. Where the perforation is inclined it may be either simple or scalari- form. The opening may be circular, elliptical, or oblong- elliptical. The elliptical form prevails where the plane of perfora- tion is oblique. Usually the end walls are not completely removed in the formation of a simple perforation and the border remaining is called the annular ridge. This ridge may vary in width from very narrow to fairly broad. There are a number of families in which all of the investigated genera have exclusively simple perforations. Prominent among these are the following: Aceracese, Bignoniacese, Ebenacese, Jug- landacese, Leguminosse, Moracese, Salicaceae, and Tiliacese. There are a number of others in which the simple type predominates but where scalariform perforations are occasionally or rarely found in the secondary wood or where, from the nature of the perforations in the primary wood, they are to be expected. Important ex- amples are the Betulacese, Fagacese and Rosacea?. Both simple and scalariform perforations may occur commonly side by side in the secondary wood, as for example, in Fagus and Platanus. Oc- casionally a segment is found in which the perforation at one end is simple and at the other scalariform. Table VII includes nearly all of the genera of native trees having vessel perforations exclu- sively or predominately simple. The representatives of the families marked with (*) exhibit some tendency toward the forma- tion of the scalariform type. The more important genera are shown in italics. ECONOMIC WOODS OF THE UNITED STATES 135 TABLE VII Indigenous Woods with Vessel Perforations Exclusively or Pre- dominantly Simple ACERACE^E Ericaceae * Parkinsonia Malus Acer Arbutus Prosopis Prunus ANACARDIACEiE Arctostaphylos Robinia Sorbus Cotinus EUPHORBIACE.E * Sophora Vauquelinia Rhus Drypetes Zygia Rubiace^e AnONACEjE FaGACEjE * Leitneriace^e Pinckneya Anona Castanea Leitneria RUTACE.E Asimina Castanopsis MAGNOLIACE.E * Amyris Betulace^e * Fagus Magnolia Fagara Carpinus Quercus acuminata Helietta Ostrya Hippocastanace^e Meliace^e Ptelea Bignoniaceje /Esculus Sivietenia Salicace^e [ Catalpa Juglandace^e MORACE.E Populus Chilopsis Hicoria Morus Salix Crescentia Juglans Toxylon Sapindace^e Boraginace^e Laurace^e * Oleace^e Exothea Ehretia Ocotea Chionanthus Hypelate Burserace^e Persea Fraxinus Sapindus Bursera Sassafras Osmanthus Ungnaria Cactace^e Umbellularia POLYGONACE^J Sapotace^e Cereus Leguminosjs Coccolobis Bumelia Opuntia Acacia RhAMNACEjE Chrysophyllum CaPPARIDACEjE Cercidium Ceanothus Sideroxylon Capparis Cercis Colubrina Simarubace^e Caprifoliace^e* Cladrastis Condalia Ailanthus (Nat.) Sambucus Dalea Krugiodendron Simaruba COMBRETACEiE Eysenhardtia Reynosia TlLIACE^E Buceras Gleditsia Rosacea * Tilia Conocarpus Gymnocladus Amelanchier UlMACEjE * Laguncularia Icthyomethia Cercocarpus Celtis Ebenace.e Leucsena Chrysobalanus Planera Diospyros Lysiloma Olneya Crataegus Ulmus Heteromeles Zygophyllace^: Lyonothamnus Guaiacum * With some tendency to scalariform, particularly in the region of primary wood. Scalariform perforations look like a grid-iron or grating with an elliptical or elongated-elliptical contour. The bars, with very rare exceptions, are arranged horizontally or transversely. As the plane is almost invariably strongly oblique and facing the ray, the structure is seen to much better advantage in radial sections than in the transverse and tangential. Macerated material is better still since a portion of the tilted plate is likely to be cut off in sectioning. Bars may also be seen in the lumina of some of the vessels in the transverse section, especially if the section is rather thick. The number of bars in a perforation varies from very few to 136 ECONOMIC WOODS OF THE UNITED STATES more than 100. Within the same species, however, the variation is within narrower limits, though the number is never constant. In Magnolia and Liriodendron, for example, the number of bars is usually less than 15 and the spaces are wide, while in Ilex, Nyssa, and Liquidambar the bars are much more numerous and are closely spaced. In the following table are listed the genera of native woods in which the vessel perforations are exclusively scalariform. In a few cases, perhaps, simple perforations will occasionally be found in association with the predominant type. The list is believed to be complete so far as the trees are concerned but not for the shrubs. Eight of the genera yield wood of commercial importance. It will be noted that no ring-porous wood is included. Scalariform per- forations are never found in large vessels, such for instance as are individually distinct to the unaided eye, presumably because the presence of gratings would interfere with the function of large vessels, namely, the rapid conduction of water in quantity. Solere- der calls attention to "the striking fact that the occurrence of scalariform perforations in the vessel often goes hand in hand with small lumina and the presence of bordered pits on the prosen- chyma." (Systematic Anatomy of the Dicotyledons, p. 1138.) TABLE VIII Indigenous Woods with Vessel Perforations Exclusively Scalariform AQUDTOLIACEiE Ilex Bettjlace^e Betula Alnus Corylus CAPRIFOLIACEiE Viburnum Cornace^e Cornus Nyssa CyRILLACEjE Cyrilla_ Cliftonia Ericaceae Rhododendron Kalmia Vaccinium Andromeda HAMAMELIDACEiE Liquidambar Hamamelis * Some simple Magnoliace^e Liriodendron Magnolia (mostly) Myricace.e Myrica* MyrtacejE Eugenia RhIZOPHORACEjE Rhizophora Saxifragace^e Philadelphus Hydrangea Ribes Symplocace^; Symplocos Staphyleace^e Staphylea Styrace^e Mohrodendron THEACE/E Gordonia perforations present in Myrica calijormca. ECONOMIC WOODS OF THE UNITED STATES 137 vessel markings: spirals and pits The first-formed elements of the primary wood, those nearest the pith, have walls characteristically marked with annular and spiral thickenings. During the process of rapid elongation of the stem these elements are stretched out, the spirals or rings sepa- rated, and the thin, unpitted walls between the thickenings are likely to be torn and broken down. Such elements comprise that portion of the primary wood known as the protoxylem. The cells of the primary wood subsequently formed make up what is known as the metaxylem. The walls of the vascular elements of the metaxylem are thickened in a scalariform (ladder-like), reticulate (net-like), or pitted (dotted) manner. The vessels (and tracheids) of the secondary wood are pitted, are without annular thickenings, and may or may not be spiral. The presence of spirals is a valuable diagnostic feature, and the vessels of smaller lumina exhibit them to best advantage. In a given wood all of the vessels may bear spirals or, especially where there is considerable variation in the size, only the smaller vessels may be thus marked. Conspicuously large vessels are invariably without spirals just as they are also without scalariform perfora- tions. Spirals exhibit considerable variation in distinctness. In some cases, as in Ulmus, they are very pronounced, in others, e.g., Tilia, they are fine but distinct, and again they may be very fine and indistinct, as in Magnolia. In some instances, as previously stated, only the overlapping tips of the segments are spiral and these are often indistinct. Tracheids which closely resemble vessel segments except in the absence of perforations, have the same markings as the vessels. Fibre-tracheids may also be spiral. This is normally the case in Ilex and occasionally in certain Rosacea?, Ericaceae, and others. The author has noted them in Arbutus and Arctostaphylos. Their presence provides a valuable diagnostic feature. 138 ECONOMIC WOODS OF THE UNITED STATES TABLE IX Indigenous Woods with Spiral Markings in Part or in All of the Vessels AcERACEiE Acer ANACARDIACEiE Cotinus Rhus Anonace.e Asimina Aquifoliace.e Ilex Betulacejs Carpinus Ostrya BlGNONIACE^E Catalpa BORAGINACE^E Ehretia CHEIRANTHODENDR.E Fremontodendron Ericaceae Arbutus Arctostaphylos Andromeda Kalmia Oxydendrum Rhododendron Vaccinium Hamamelidace^e Liquidambar HlPPOCASTANACE^E Msculus Leguminos^e Cercis Gleditsia Gymnocladus Robinia LEITNERIACE.E Leitneria Magnoliace^e Magnolia Meliace.e Melia (Nat.) Morace^e Broussonetia (Nat.) Morus Toxylon Oleace^e Chionanthus Osmanthus Rhamnace.e Ceonothus Rhamnus Rosace.e Amelanchier Aronia Cercocarpus Prunus Pyrus (in part) Rosa Sorb us ScROPHULARL\CE.E Paulownia (Nat.) SlMARUBACE.E Ailanthus (Nat.) Koeberlinia Tiliace.e Tilia Ulmace.e Celtis Ulmus Planera The vessels of secondary wood are always pitted. (See pits, p. 31.) This feature is seen to best advantage in macerated material, especially where the vessels are so large that most of the wall is cut away in sectioning. The nature of the pitting is de- termined by the contiguous elements. The number, form, and arrangement of the pits on a given area of wall depends upon the particular kind of cell in contact there and the breadth of the sur- face of contact. The character of the pitting between adjacent vessels and between vessels and ray parenchyma is the most im- portant for diagnostic purposes. Pits between vessels are invariably bordered. The features worthy of special notice are the arrangement of the pits, the size and contour of the border, and the nature of the pit mouths. It is very common to find vessels in groups so compressed that the walls of mutual contact are flattened out broadly. In walls thus flattened it is not uncommon to find pits that are greatly elongated ECONOMIC WOODS OF THE UNITED STATES 139 transversely and arranged in a vertical series like the rungs of a ladder. This scalariform pitting is characteristic of the vessels in Magnolia, is common in Liriodendron and Nyssa, less so in Liqui- dambar, Ilex and Platanus, and of sporadic occurrence in Castanea, Castanopsis, Quercus, and some others. Since radial grouping is the most common, the pitted surfaces usually appear to better advantage in tangential than in radial sections. Pits between vessels and ray cells are simple on the ray side but may be bordered, simple, or transitional on the other. These TABLE X Nature of Pitting of Vessel Wall where in Contact with Ray Parenchyma Family Bor- dered Simple Family Bor- dered Simple Aceraceae X x Anacardiaceae. XXX XXX XX X x XX X Moraceae X > Anonacese x Aquifoliaceae x Araliacese X > Nyctaginaceae Bignoniaceae X X X x Boraginaceae Burseraceae Canellaceae Capparidaceae Caprifoliaceae Rhizophoraceae Rosacea? X ► X 1 Celastraceae X X X X X X X Cornaceae X — » ■Cyrillaceae 1 x X Ebenaceae Ericaceae X X Euphorbiaceae X > < X < X X X x 1 X x Tx Simarubaceae X Fagaceae X X x Hamamelidaceae Styraceae Hippocastanaceae. . . . Symplocaceae Juglandaceae X Y Koeberliniaceae Tiliaceae X X X X Lauraceae X Leguminosae f Verbenaceae Zygophyllaceae Magnoliaceae * In Betula and Alnus the pits are bordered; in Carpinus, Corylus, and Ostrya simple pits predominate. t In Robinia the pits are predominately simple. 140 ECONOMIC WOODS OF THE UNITED STATES pits may be very small, medium or large, often with considerable variation in the same specimen. In woods with heterogeneous rays the marginal cells are usually more prominently pitted than the others. In Gordonia and Oxydendrum the pits are simple or only slightly bordered and are frequently in scalariform ar- rangement. In Sideroxylon and Chrysophyllum many of the pits are small and bordered while others are large, simple or nearly so, elliptical or elongated-elliptical and disposed horizontally, verti- cally or diagonally, resembling perforations rather than pits. In Magnolia it is common to find much elongated borders about groups of small pits. Table X gives for the different families the dominant type of pits in vessels where in contact with the rays. Where both types are indicated with connecting line it refers to their occur- rence side by side in the same wood; otherwise in different woods of same family. An arrow indicates transitions from the pre- vailing type. VESSEL CONTENTS The principal contents of vessels that have ceased to function actively as water-carriers are (a) tyloses (parenchymatous in- trusions) and (6) various deposits or excretions such as gums, resins, lime, etc. Sometimes such features are constant and con- spicuous enough to be of value for diagnostic purposes. In a great many cases, however, there is too much variation for dependable results. Generally it is merely a question as to whether the pores appear open or closed rather than exact determination by micro- scopic means of the presence or absence of certain contents. The feature is of most importance in woods with large pores. The following table gives the results of some investigations by the author on the occurrence of tyloses and gum deposits in in- digenous woods and a few that have been introduced. The find- ings do not in all cases agree with those of other investigators and in some instances are not to be considered as final, especially where non-occurrence is indicated, owing to the great likelihood of varia- tion in different specimens. ECONOMIC WOODS OF THE UNITED STATES 141 TABLE XI Occurrence of Tyloses and Gum Deposits in Vessels of Indigenous Woods Acacia Acer ^Esculus Ailanthus (Nat.). . . Alnus Amelanchier Amyris Anona Arbutus Arctostaphylos Asimina Avicennia Betula Broussonetia (Nat.) Bumelia Bursera Carpinus Castanea Castanopsis Catalpa Celtis Cercidium Cercocarpus Chilopsis Cladrastis Cornus €otinus Crataegus Diospyros Eucalyptus (Int.). . Fagus Ficus Fraxinus Fremontodendron. . Gleditsia Guaiacum Gymnocladus Hamamelis Hicoria (Carya) Ilex Juglans Kalmia Tyloses few absent few- absent common absent absent abundant common abundant common absent abundant absent abundant absent abundant abun-few absent abundant absent abundant absent common occasional occasional common common common rare common Leitneria Liquidambar Liriodendron Magnolia Melia (Nat.) Mohrodendron. . Morus Nyssa Olneya Ostrya Oxydendrum Parkinsonia Paulownia (Nat.) Persea Planera Platanus Populus Prosopis Prunus Ptelea Pyrus Quercus (white) . , (red).... (live) Rhamnus Rhizophora Rhododendron . . Rhus Robinia Salix Sambucus Sapindus Sassafras Swietenia Symplocos Tilia Toxylon Ulmus Umbellularia Vaccinium Viburnum Xanthoxylum Tyloses absent common few absent abundant absent common absent abundant common absent few common absent common absent abun-few few-abun. absent absent abundant abundant common absent common absent abundant few-abun. absent common occasional common common occasional 142 ECONOMIC WOODS OF THE UNITED STATES RING-POROUS AND DIFFUSE-POROUS WOODS There are 36 indigenous genera, exclusive of shrubs and vines,, with ring-porous woods, at least in part, and 4 that have become thoroughly naturalized in the United States. These 40 genera are representatives of 20 families of which only four, each con- sisting of a single genus, are exclusively ring-porous. Sixteen of these genera supply wood of more or less economic importance. In the case of Quercus the live oaks are mostly diffuse-porous, while one species of Hicoria and one or two of Ulmus are rather intermediate, at least in certain instances. Some species of Prosopis are diffuse-porous and some other genera, e.g., Leitneria and Ptelea, produce woods which require rather close observation to note their ring-porous nature. There are 35 families whose indigenous representatives are- exclusively diffuse-porous. Eleven of these families include 15 genera of economic woods. Of a total of 147 indigenous dicotyle- donous woods, 113 or nearly 80 per cent are diffuse-porous. Inso- far as the economic woods are concerned, however, the division is. about equal. ECONOMIC WOODS OF THE UNITED STATES 143 TABLE XII Families with Indigenous Representatives Exclusively Diffuse-porous Aceracese Aquifoliacese Betulaceae Boraginaceae Burseracese Canellaceae Capparidaceae Caprifoliaceae Caricaceae (?) Celastracese Combretaceae Cornaceae Cyrillaceae Ericaceae Euphorbiaceae Hamamelidaceae Hippocastanaceae Koeberliniaceae Magnoliaceae Myricaceae Myrsinaceae Myrtaceae Nyctaginaceae Platanaceae Polygonaceae Rhamnaceae Rhizophoraceae Rosaceae Salicaceae Styraceae Symplocaceae Theaceae Theophrastaceae Tiliaceae Zygophyllaceae TABLE XIII Indigenous Ring-porous Woods Acacia Ailanthus (Nat.) Asimina Avicennia Broussonetia (Nat.) Bumelia Castanea Castanopsis Catalpa Celtis Cercis Chilopsis Chionanthus Cotinus Dalea Diospyros Ehretia Eysenhardtia Fraxinus Fremontodendron Gleditsia Gymnocladus Hicoria (Carya) Leitneria Melia (Nat.) Moms Paulownia (Nat.) Parkinsonia Pinckneya Prosopis Ptelea Que re us Rhamnus Rhus Robinia Sapindus Sassafras Sophora Toxylon Ulmus 144 ECONOMIC WOODS OF THE UNITED STATES TABLE XIV Nature of Pitting in Wood Fibres of Indigenous Woods Acacia Acer JSsculus Ailanthus (Nat.) Alnus Amelanchier Amyris Andromeda Anona Arbutus Arctostaphylos Asimina Avicennia Betula Broussonetia (Nat.). Bumelia Bursera Carpinus Castanea Castanopsis Catalpa Ceanothus Celtis Cercis Cercocarpus Chilopsis Chionanthus Chrysophyllum Cladrastis Cornus Cotinus Crataegus Cyrilla Diospyros Eucalyptus (Int.). • • Fagus Ficus Fraxinus Fremontodendron. . . Gleditsia Gordonia Guaiacum Gymnocladus Hamamelis Hicoria (Carya) Ilex Smi*» derTd Juglans Kalmia Leitneria Liquidambar Liriodendron Magnolia Melia Mohrodendron. . . . Morus Myrica Nyssa Ocotea Olneya Ostrya Oxydendrum Parkinsonia Paulownia (Nat.). Persea Planera Platanus Populus Prosopis Primus Ptelea Pyrus Quercus Rhamnus Rhizophora Rhododendron.. . Rhus Robinia Salix Sambucus Sapindus Sassafras Sideroxylon Swietenia Symplocos Tilia Toxylon Ulmus Umbellularia .... Vaccinium Viburnum Xanthoxylum. . . . Bor- dered Arrows indicate transitions from the prevailing type. ECONOMIC WOODS OF THE UNITED STATES 145 TABLE XV Kinds of Rays in Indigenous Dicotyledonous Woods Genus Homo- geneous Hetero- geneous Genus Homo- geneous Hetero- geneous X X X — X X X X X X X— X X— X X X— X X— X X Ailanthus (Nat.) X X X X X Liquidambar Liriodendron X X X Melia (Nat.) X Mohrodendron Morus X X X X X I X X X X — X X Arctostaphylos X X Olneya X Broussonetia (Nat.)... X Paulownia (Nat.) X X X < X X > X X X X — X X X — X X X X Celtis — X Ptelea — X Chrysophyllum X Rhododendron X X Cyrilla 1 x 1 x < X X Eucalyptus (Int.) Fagus X X X X X X X X X 1 X X X Tilia . 1 Umbellularia Gymnocladus X X Hicoria (Carya) Ilex X > 1 X Xanthoxylum X Arrows indicate transitions from the prevailing type. 146 ECONOMIC WOODS OF THE UNITED STATES TABLE XVI Indigenous Woods with "Ripple Marks Species No. per inch Remarks 58-68 200 120-128 200 150-160 110-115 120 150 55-80 250 150-160 50-55 160 45-55 55-80 5.5-60 55-60 Artemisia tridentata Baccharis sarathoides Biglovia graveolens Shrub; rays not storied Many rays 2-storied Crescentia curcubitina Dalbergia brownei Lines irregular Shrub; marks visible Rays not storied Lines usually wavy Diospyros virginiana Distinct only in inner bark Often irregular Rays not storied Often absent Sophora secundiflora Swietenia mahagoni it ti a PROPERTY LIBRARY N. C. State College INDEX Abies 23, 29, 30, 45, 64, 127 amabilis 52,80 balsamea 17,52, 80 concolor 17, 52, 80 grandis 17, 52, 80 magnifica 52, 80 nobilis 52,80 Acacia. . . .68, 135, 141, 143, 144, 145 Acer 7, 27, 40, 43, 44, 47, 64, 66, 129, 135, 138, 141, 144, 145 macrophyllum 102 negundo 52,102 californicum 102 nigrum 102 rubrum 20, 37, 51, 103 saccharinum 37, 103 saccharum 37, 47, 51, 102 Aceracea? 36, 129, 134, 135, 138, 139, 143 jEsculus 7, 15, 22, 24, 25, 27, 40, 47, 64, 129, 135, 138, 141, 144, 145, 146 calif ornica 51, 107 glabra 52,107 octandra 39,107 Aggregate rays 27 Ailanthus 7, 135, 138, 141, 143, 144, 145 Alder 107,129 Algaroba 91 Alnus 7, 26, 51, 105, 107, 129, 136, 139, 141, 144, 145 Amelanchier. . .135, 138, 141, 144, 145 Amyris 135, 141, 144, 145 Anacardiaceae 135, 138, 139 Andromeda 136, 138, 144, 145 Angiosperms 6, 11, 127, 129 Annual rings 40-43 Annular ridge 134 Anona 8,135,144,145 Anonaceae 135, 138, 139 Appendix 127 Apple 104 Aquifoliacese 128, 129, 136, 138, 139, 143 Araliacese 139 Arborvitae 84 Arbutus 135, 137, 138, 141, 144, 145 Arctostaphylos 135, 137, 138, 141, 144, 145 Arizona white pine 76 Aronia 138 Artemisia 146 Ash 92,93, 129 Asimina 8, 52, 135, 138, 141, 144, 145 Aspen 108 Avicennia 141, 143, 144, 145 Axyris 133 Baccharis 146 Bald cypress 82 Balsam fir 79,80 Bark 5, 8-10, 127 Basswood 106, 129 Bast fibres 8, 66 Bay 106 poplar 105 Beech 101, 129 Betula 7, 10, 15, 27, 37, 43, 64, 66, 68, 129, 136, 139, 141, 144, 145 lenta 37, 51, 65, 103 lutea 37, 51, 103 nigra 20, 37, 51, 103 papyrifera 37, 51, 104 populifolia 37, 104 Betulaceaa 36, 129, 134, 135, 138, 139, 143 147 148 INDEX Big shellbark hickory 95 Biglovia 146 Bignoniacese 128, 129, 134, 135, 138, 139 Bigtree 81 Birch 103, 129 Bitternut hickory 95 Black ash 93 birch 103 cherry 102, 129 gum 105 jack oak 87 locust 129 maple 102 oak 87 spruce 79 walnut 96 willow 99, 108 Blue ash 94 beech 99 gum 98 Boraginacese 135, 138, 139, 143 Bordered pits 16, 31-35, 131 Boxelder 99 Broadleaf woods 7, 17, 85 Brousonnetia 138, 141, 143, 144, 145 Brown ash 93 " cottonwood" 108 Buceras 135 Buckeye 107, 129 Bull pine 76 Bumelia 135, 141, 143, 144, 145 Bur oak 88 Bursera 135, 141, 144, 145 Burseraceae 135, 139, 143 Butternut 96 Buttonball 100 Cactace^e 135 Caesalpina 65 Caesalpinese 30 Calcium oxalate 21 California black oak 87 buckeye 107 laurel 98 Calif ornia nutmeg 85 walnut 96 white pine 76 Cambium 11,12 Camphor trees 68 Camphora 68 Canella 134 Canellaceae 139, 143 Canoe cedar 84 Capparidaceue 135, 139, 143 Capparis 135 Caprifoliacese 135, 136, 139, 143 Caricacese 143 Carpinus, 9, 26, 41, 51, 99, 135, 138, 139, 141, 144, 145 Carya (see Hicoria) Case-hardening 58 Castanea 20, 40, 47, 48, 52, 68, 69, 129, 135, 139, 141, 143, 144, 145 dentata 57, 86 pumila 51, 86 Castanopsis 51, 86, 129, 135, 139, 141, 143, 144, 145 Cat spruce 79 Catalpa 44, 64, 68, 92, 129, 135, 138, 141, 143, 144, 145 bignoniodes 92 catalpa 52, 92 speciosa 52, 92 Ceanothus 135, 138, 144, 145 Cedar 82, 83, 127 elm 90 -like woods 127 Cedrus 80 Celastracese 139, 143 Cell wall 130 Celtis 20, 25, 27, 44, 45, 51, 129, 135, 138, 141, 143, 144, 145 mississippiensis 89 occidentalis 89 Cercidium 67, 135, 141 Cercis. . .135, 138, 143, 144, 145, 146 Cercocarpus. .135, 138, 141, 144, 145 Cereus 135 Chamaecyparis 64, 80, 127 149 Chamaecyparis Iawsoniana 20, 52, 67, 68, 69, 83 nootkatensis 51, 68, 83 sphseroidea 85 thyoides 20, 68, 85 Checking of wood 56 Cheiranthodendrae 138 Cheirodendron 134 Cherry 102, 129 birch 103 Chestnut 86, 129 oak 88 Chilopsis 141, 143, 144, 145 Chinquapin 86, 129 chestnut 86 oak 88 Chionanthus 135, 138, 143 Chrysobalanus 135 Chrysophyllum. . . . 135, 140, 144, 145 Cinnamomum 68 Cladrastis 64, 96, 135, 141, 144, 145 Chlorophora 65 Cliftonia 136 Chilopsis 135 Coccolobis 135 Coffee tree 92, 129 Color of wood 64-66 Colubrina 135 Combretaceae 135, 143 Common catalpa 92 Compositse 133 Composite perforations 133-4 " Compression wood" 77 Condalia 50, 135 Conductivity 62 Conifera: 6, 127 Conjugate cells 25 Conocarpus 135 Cork 9, 10 cambium 9 Cornacese 129, 136, 139, 143 Cornus, 7, 15, 100, 129, 136, 141, 144, 145 florida 51, 101 nuttallii 101 Cortex 8 Corylus 136, 139 Cotinus, 135, 138, 141, 143, 144, 145 Cottonwood 99, 108, 129 Cow oak 88 Crataegus. 51, 128, 135, 141, 144, 145 Crescentia 135, 146 "Cross-field" 74 Crystals 9, 19, 21 Cuban pine 77 Cucumber tree 106, 129 Cupressus 51, 127 Cypress 82, 127 Cyrilla 136, 144, 145 Cyrillacea; 136, 139, 143 Dalbergia 146 Dalea 135, 143 Density 49-52 Dicotyledons, 7, 13, 14, 21, 30, 41, 61, 85, 127, 128, 129 Didymopanax 134 Diffuse-porous woods, 16, 43, 95, 142-3 Diospyros 21, 22, 39, 51, 64, 94, 129, 135, 141, 143, 144, 145, 146 Dipterocarpese 30 Dogwood 129 Douglas fir 78, 127 pine 78 spruce 78 Drimys 14 Drying of wood 53 Dryobalanus 68 Drypetes 135 Ducts, gum 30 resin 9, 23, 29-31, 78 Dyewoods 65 Eastern hemlock 81 Ebenaceaj. . . . 128, 129, 134, 135, 139 Ehretia 135, 138, 143 Elements of wood 13, 131 Elm 89, 129 Epidermis 8 150 INDEX Epithelial cells 22, 78, 132 Ephedra 134 Ericaceae. 135, 136, 137, 138, 139, 143 Eucalyptus. .47, 57, 98, 141, 144, 145 Eugenia 136 Euphorbiacea? 135, 139, 143 Evergreen oak 98 Exothea 135 Eysenhardtia 135, 143 Fagace^ 129, 134, 135,139 Fagara 66, 135 Fagus 7, 9, 20, 26, 43, 44, 47, 51, 66, 100, 101, 129, 134, 135, 141, 144, 145 False rings 41 Fascicular cambium 12 Fibres 13, 18-20, 88 Fibre-saturation point 54 tracheids 132 Fibrous elements 13, 131 Fibro-vascular bundles 7, 12 Ficus 141, 144, 145 Fir 80, 127 Five-leaved pines 74 Flowering dogwood 101 Foxtail pines 75, 78 Fraxinus 7, 25, 27, 40, 44, 47, 48, 64, 129, 141, 143, 144, 145 americana 22, 51, 94 lanceolata 51, 94 nigra 22, 93 oregona 51, 93 pennsylvanica 51, 94 profunda 94 quadrangulata 51, 94 Fremontodendron 138, 141, 143, 144, 145 Fusiform rays 25, 29 Fustic 65 Giant arborvit^e 84 sequoia 81 Gleditsia 15, 51, 92, 129, 135, 138, 141, 143, 144, 145 Gloss 66-67 Gordonia 136, 140, 144, 145 Grain 46-48 Gray birch 104 Green ash 94 Growth rings 16, 40-43 Guaiacum 15, 50, 66, 97, 135, 138, 141, 144, 145, 146 Gum 15, 140-1 ducts 30 -wood 105 Gymnocladus 7, 15, 44, 47, 51, 92, 129, 135, 141, 143, 144, 145 Gymnosperms 6, 7, 11, 13, 16, 25, 31, 38, 40, 43, 61, 73, 127, 129 Hackberrt 89, 129 Hackmatack 79 Haematoxylon 65 Hamamelidacese 129, 136, 138, 139, 143 Hamamelis 136, 141, 144, 145 Hard maple 102 -woods 7, 85 Hardy catalpa 92 "Hazel" 105 Heartwood 6, 44-45, 64 Helietta 135 Hemlock 32, 80, 127 Heterogeneous rays 24, 25, 145 Heteromeles 135 Hickory 92, 95, 129 elm 89 Hicoria 2, 21, 22, 44, 66, 129, 135, 141, 142, 143, 144, 145 alba 20, 50, 57, 95 aquatica 51, 95 glabra 51, 95 laciniosa 10, 51, 95 minima 95 myristicsef ormis 95 ovata 95 pecan 95 Hippocastanaceae 128, 129, 135, 138, 139, 143 INDEX 151 Holly 100, 129 Homogeneous rays 25, 145 Honey locust 92, 129 "Honey-combed" wood 58 Hop hornbeam 99 Hornbeam 99 Hydrangea 136 Hygroscopicity 59-60 Hypelate 135 ICTHYOMETHIA 136 Idaho white pine 75 Ilex 19, 20, 45, 51, 64, 65, 100, 129, 136, 137, 138, 139, 141, 144, 145 Incense cedar 83 Interfascicular cambium 12 Intermediate fibers 25, 132 Ironwood 99 Juglans 7, 8, 15, 21, 65, 129, 135, 141, 144, 145 calif ornica 96 cinerea 52, 57, 95, 96 nigra 20, 61, 66, 96 Juglandacese 134, 135, 139 Juniper 84, 127 Juniperus 10, 22, 41, 44, 45, 47, 51, 64, 68, 80, 84, 127 barbadensis 84 virginiana 49, 57, 66, 67, 68, 84 Kalmia 136, 138, 141, 144, 145 Kentucky coffee tree 92, 129 Key to woods 73 "Knees" of cypress 82 Knots 48-49 Kceberlinia 138 Kceberliniaceae 139, 143 Krugiodendron 135 Laguncularia 135 Larch 78, 127 Larix 25, 29, 31, 36, 127 americana 46, 51, 79 laricina 79 Larix occidentals 17, 51, 79 Laurel oak 87 Lauraceae 128, 129, 135, 139 Leguminosae.,129, 134, 135, 138, 139 Leitneria 31, 50, 52, 135, 138, 141, 142, 143, 144, 145 Leitneriacese 135, 138, 139 Leucsena 135 Libocedrus 17, 22, 52, 68, 69, 80, 83, 127 Libriform fibres 131, 132 Lignumvitae 97 Lin 106 Liquidambar 14, 19, 20, 30, 33, 40, 47, 51, 57, 64, 105, 129, 136, 138, 139, 141, 144, 145 Liriodendron 8, 10, 15, 20, 22, 35, 43, 45, 52, 57, 64, 106, 129, 136, 139, 141, 144, 145 Lithospermum 134 Live oak 16, 98 Loblolly pine 77 Locust 91, 129 Lodgepole pine 76 Longleaf pine 77 Lowland fir 80 Luster 66-67 Lyonothamnus 135 Lysiloma 135 Maceration of wood 4 Madura 91 Magnolia 8, 15, 22, 35, 40, 51, 129, 136, 137, 138, 139, 140, 141, 144, 145 acuminata 15, 20, 51, 106, 135 glauca 51, 106 Magnoliacese 14, 33, 129, 135, 136, 138, 139, 143 Mahogany 92, 97, 129 Malus 135 Maple 63, 102, 129 Medullary rays 21, 23 spots 36 Meisteria 134 152 INDEX Melia 138, 141, 143, 144, 145 Meliacege 128, 129, 135, 138, 139 Menziesii 134 Mesquite 91, 129 Metaxylem 11, 137 Middle lamella 130 Mockernut hickory 95 Mohrodendron. . ..136, 141, 144, 145 Monocotyledons 7, 127-8, 129 Moracea? 128, 129, 134, 135, 138, 139 Morus 44, 51, 64, 65, 90, 129, 135, 138, 141, 143, 144, 145 Mulberry 90, 129 Multiperf orate perforations. ... 134 Myrica 136, 144, 145 Myricacese 136, 139, 143 Myrsine 139, 143 Myrtacese 136, 139, 143 Negundo 102 New Mexico white pine 76 Noble fir 80 Non-porous woods 73 North Carolina pine 77 Northern pine 75 Norway pine 76 Nut pine 75, 78 Nutmeg 85 hickory 94 Nyctaginaceee 139, 143 Nyssa 8, 45, 47, 57, 64, 99, 129, 136, 139, 141, 144, 145 aquatica 105 biflora 105 sylvatica 20, 24, 51, 57, 105 Oak 16, 87, 129 Ocotea 135, 144, 145 Odor of wood 67-68 Ohio buckeye 107 Oleacea? 129, 135, 138, 139 Olneya 135, 141, 144, 145, 146 Opuntia 135 Oregon ash 93 oak 88 Oregon pine 78 Osage orange 91, 129 Osmanthus 135, 138 Ostrya.50, 99, 135, 139, 141, 144, 145 Overcup oak 88 Oxydendrum..l38, 140, 141, 144, 145 Palms 128 Paper birch 104 Parenchyma. .19, 21-23, 86, 131, 132 Parenchymatous elements 13, 131 tracheids 17, 27 Parkinsonia 67, 135, 141, 143, 144, 145 Pasania 98 Paulownia.. . .138, 141, 143, 144, 145 Pecan hickory 95 "Pecky" or "peggy" cypress. . 82 cedar 83 Pencil cedar 84 Pepperidge 105 Pepperwood 98 Perforations of vessels 14, 15, 131, 133-6 pit membranes 34 Pericycle 8 Permeability of wood 60-62 Persea 135, 141, 144, 145 Persimmon 92, 94, 129 Phelioderm 9 Phellogen 9 Philadelphus 136 Phloem 8, 11, 129 Physical properties of wood 2, 5, 49-69 Picea 25, 27, 29, 31, 36, 45, 52, 64, 77 79, 127 alba 52, 79 canadensis 79 engelmanni 17, 52, 79 mariana 79 nigra 52, 79 rubens 17, 79 rubra 79 sitchensis 17, 52, 79 INDEX 153 Pignut hickory 95 Pin oak 87 Pinckneya 135, 143 Pine 74, 127 Pink oak 88 Piiion pine 75 Pmus 2, 10, 23, 25, 27, 28, 31, 33, 67, 68, 69, 79, 127 albicaulis 52, 74 aristata 51, 75 australis 77 balfouriana 51, 75 caribaea 77 cembroides 75 contorta 76 cubensis 77 densiflora 76 echinata 17, 51, 77 edulis 17, 51, 26, 75 flexilis 52, 74 heterophylla 45, 51, 77 lambertiana 17, 52, 75 laricio 76 mitis 77 monophylla 51, 75 monticola 17, 52, 65, 75 murrayana 17, 38, 52, 76 palustris 7, 17, 44, 48, 51, 53, 55, 69, 77 ponderosa 17, 30, 31, 51, 76 quadrif olia 75 resinosa 17, 27, 34, 51, 76 strobiformis 74 strobus 17, 25, 45, 52, 65, 75 sylvestris 76 tseda 17, 45, 48, 51, 55, 77 virginiana 17 Pith 5,7-8, 127 flecks 36-37 rays 21-27, 145 Pits 15,31-35, 131 Planera 135, 138, 141, 144, 145 Plant food 130 Platanacea 129, 139, 143 Platanus 10, 26, 66, 129, 134, 141, 144, 145 occidentalis 20, 47, 51, 100 racemosa 100 wrightii 100 Polygonaceae 135, 139, 143 Poplar 106, 109, 129 Popple 108 Populus 2, 7, 15, 25, 45, 47, 64, 67, 129, 135, 141, 144, 145 deltoides 20, 108 grandidentata 20, 52, 108 heterophylla 20, 52, 108 tremuloides 52, 108 trichocarpa 20, 52, 108 Pores : 15 Porous woods 85 Port Orford cedar 86 Post oak 88 Primary tissues 11, 137 rays 23 Procambium 11 Procumbent ray cells 24 Prosenchyma 131 Prosopis 15, 51, 64, 65, 91, 129, 135, 141, 142, 143, 144, 145 Protoderm 11 Protoxylem 11, 137 Prunus 30, 47, 51, 102, 128, 129, 135 138, 141, 144, 145 Pseudotsuga 7, 16, 17, 23, 25, 27, 29 31, 36, 48, 51, 77, 78, 127 Ptelea. .135, 141, 142, 143, 144, 145 "Punk" ash 93 Pumpkin ash 94 Pyrus 51, 104, 138, 141, 144, 145 Qtjercus 2, 7, 10, 14, 15, 21, 25, 40, 47, 48, 50, 67, 68, 129, 135, 139, 141, 142, 143, 144, 145 acuminata 88 agrifolia 50, 98 alba 20, 45, 47, 51, 88 bicolor 88 calif ornica 87 154 INDEX Quercus chrysolepis 50, 9S coccinea 20, 51, 87 densiflora 98 digitata 87 falcata S7 garryana 88 hypoleuca 95 imbricaria 51, 87 laurifolia 51, 87 lyrata 88 macrocarpa 42, 51, 88 marilandica 36, 87 michauxii 20, 51, 88 minor 88 muhlenbergii 88 nigra 51, 87 palustris 51, 87 phellos 51, 87 platanoides 88 prinus 6, 51, 88 rubra 20, 51, 87 stellata 88 suber 10. texana 50, 87 velutina 51, 87 virginiana 20, 98 wislizeni 98 Quillaja 134 Ray parenchyma 13, 27, 132 tracheids 13, 27, 76, 80, 132 Rays 21, 26-28, 145 Red alder 97 ash 94 birch 103 cedar 83, 84 elm 89 fir 78,80 gum 105, 129 hickory 95 maple 103 mulberry 90 oak 87, 141 pine 27, 34, 76 spruce 79 Red-wood 81 Resin cells 22-23 cysts 29 ducts 9, 23, 29-31 Resinous tracheids 17, 74 Resonance 62-63 Reynosia 135 Rhamnaceae 135, 138, 139, 143 Rhamnus 138, 141, 143, 144, 145 Rhizophora 135, 141, 144, 145 Rhizophoracese 135, 139, 143 Rhododendron 125, 138, 141, 144, 145 Rhus 7, 66, 135, 138, 141, 143, 144, 145 Ribes 135 Ring, growth . . '. 40-43 -porous woods 16, 40, 42, 86 "Ripple marks" 39, 146 River birch 103 Robinia 10, 19, 35, 40, 44, 45, 51, 64, 66, 91, 129, 131, 135, 138, 139, 141, 143, 144, 145 Rock elm 89 maple 102 oak 88 Rosa 133, 134, 138 Rosacea 36, 128, 129, 133, 134, 135, 137, 138, 139, 143 Rotholz 77 Rubiaceae 135, 139 Rutacea 135, 139 Salicace.e 36, 134, 135, 139, 143 Salix 7, 15, 20, 25, 45, 47, 52, 64, 108, 129, 135, 141, 144, 145 Sambucus 7, 135, 141, 144, 145 Sanio's beams 38 Santalum 68 Sapindacese 135, 139 Sapindus 135, 141, 143, 144, 145 Sapotaceae 135, 139 Sapwood 6, 44, 64 Sassafras 24, 26, 27, 44, 51, 64, 68, 69, 92, 129, 135, 141, 143, 144, 145 Saxifragaceae 136 155 Scalariform markings 33 perforations 15, 133, 135-6 pits 33, 139, 140 Scarlet oak 87 Scent 67-68 Scrophulariacese 138 Seasoning 53 "Second-growth" 42, 95 ■Secondary rays 23 rings 41 wall 31 wood 12-13 Sectioning wood 2-3 Segments, vessel 14, 131, 132-3 ■Semi-bordered pits 32 Septate fibers 18, 132 Sequoia 10, 22, 23, 29, 47, 64, 66, 80, 81, 127 gigantea 81 sempervirens 17, 23, 52, 82 washingtoniana 17, 52, 81 Shagbark hickory 95 Shellbark hickory 95 Shingle cedar 84 oak 87 Shortleaf pine 80 Shrinkage 56-59 Sideroxylon 135, 140, 144, 145 Sidonia 134 Sieve tubes 8, 129 Silver maple 103 Simaruba 135, 146 Simarubacese 135, 138, 139 Simple perforations 14, 133-5 pits 28, 31, 131 Sitka cypress 83 spruce 79 Slash pine 77 Slippery elm 89 Soft ash 93 maple 103 pine 27, 74 -woods 7, 73 Sophora 135, 143, 146 Sorbus 134, 135, 138 Sour gum 105 Southern cypress 82 pine 77 red cedar 84 oak 87 swamp white oak 88 Spanish oak 87 Specific gravity 49-52 Spirals 17,76, 77, 132 Spotted oak 87 Spruce 63, 78,79, 127 Staphylea 136 Staphylacese 136 Sterculiaceae 139 Stinking cedar 85 stone cells 8,9 Striations 77 Structural properties 1, 5, 130 Styracea? 136, 139, 143 Substitute fibres 25, 132 Sugar maple 102 pine 75 -berry 89 Swamp white oak 88 Sweet bay 106 birch 103 gum 105 locust 92 Swietenia 18, 30, 39, 51, 64, 97, 129, 135, 141, 144, 145, 146 Sycamore 100, 129 Symplocacese 136, 139, 143 Symplocos 136, 141, 144, 145 79 95 7, 8, 10 Taste of wood 69 Taxacese 6, 7, 13, 22, 85, 127 Taxodium 10, 22, 34, 47, 52, 64, 66, 68, 80, 82, 127 Taxus 7, 10, 16, 44, 77, 80, 127 brevifolia 51, 85 floridana 51, 85 Terminal parenchyma 22 156 INDEX Tetracentron 14 Texture 46-48 Theacete 136, 139, 143 Theophrastaceae 143 Thorn tree 92 Thuya 22, 68,80, 127 gigantea 84 occidentalis 17, 52, 84 plicata 17, 23, 52, 84 Tier-like structure 39, 165 Tilia 7, 10, 15, 22, 27, 64, 129, 135, 137, 138, 141, 144, 145 americana 20, 39, 45, 52, 106, 146 heterophylla 39, 52, 106, 146 pubescens 39, 52, 106, 146 Tiliaceae 129, 134, 135, 138, 139, 143 Toxylon 34, 51, 138, 141, 143, 144, 145 Trabecular 38 Tracheids 13, 15, 16-18, 132 Traumatic resin ducts 30, 32, 80 Trochodendracese 14 Trochodendron 14 Tsuga.10, 22, 27, 29, 34, 45, 64, 127 canadensis 17, 32, 52, 68, 81 heterophylla 17, 66, 80, 81 Torreya 106, 129 Tumion 16, 51, 77, 80, 85, 127 Tupelo 105, 129 Turkey oak 88 Tyloses 15, 35, 36, 60, 140-1 Ulmace^e 135, 138, 139 Ulmus 7, 25, 27, 48, 68, 129, 135, 137, 138, 141, 142, 143, 144, 145 alata 51, 90 americana 20, 51, 89 crassifolia 51, 90 f ulva 89 pubescens 51, 89 racemosa 51, 89 Umbellularia 135, 141, 144, 145 Ungnaria 135 Vaccinium 134, 136, 138, 141, 144, 145 Vascular bundles 11 elements 13, 131 Vauquelinia 135 Verbeniacese 139' Vessels.. .13, 14-16, 75, 131, 132-143 Viburnum 68, 136, 141, 144, 145 Violet wood 68 Walnut 96, 129 Warping 56-59 Water content 52-55 beech 99 hickory 95 oak 87 Weight of wood 49-52 Western chinquapin 86 dogwood 107 hemlock 80 larch 79 pine 75, 76 red cedar 84 soft pine 76 white pine 75 yellow pine 30, 31, 76 White ash 94 bay 106 birch 103, 104 cedar 84, 85 elm../. 89 fir 80 hickory 95 mulberry 90 oak 16, 88 pine 74, 75 spruce 82 walnut 96 -wood 106 Willow 108, 128, 129 oak 87 Winged elm 90 Wood cells 19, 130 fibres 13, 18-20 parenchyma 19, 21-23, 86, 130, 132 structure 130 tracheids 13, 16-1& INDEX 157 Xanthoxylum .... 65, 141, 144, 145 Yellow oak 87 Xylem . .5, 11 Yellow birch 103 buckeye 107 cedar 82, 83 chestnut oak 88 cypress 83 fir 78 locust 91 popular 106 -wood 96 Yew 85, 127 Yucca 128 Zygia 135 Zygogynum 14 Zygophyllaceae 135, 139, 143 DESCRIPTION OF PLATES All photomicrographs (except frontispiece) show magnification of 50 diameters PLATE I. DESCRIPTION OF PLATE I. Map of the United States showing Natural Forest Regions. PLATE II. DESCRIPTION OF PLATE II. Fig. 1. — Taxodium distichum (bald cypress): cross section through portions of two growth rings. Several resin cells are visible near the lower edge. Fig. 2. — Tsuga canadensis (eastern hemlock): cross section. Note decided contrast between early and late wood. Fig. 3. — Juniperus virginiana (red cedar) : cross section through median portion of growth ring showing zonate arrangement of resin cells. Fig. 4. — The same: cross section showing very thin late wood ; also doubling of the late wood, producing "false ring." Note small size of tracheids. Fig. 5. — Quercus alba (white oak) : cross section showing small pores with thin walls and angular outlines and in broad band; large pores with tyloses. Fig. 6. — Quercus rubra (red oak) : cross section showing small pores with thick walls and circular outlines, and in narrow band ; large pores without tyloses. PLATE II. PLATE III. DESCRIPTION OF PLATE III. Fig. 1. — Quercus alba (white oak) : tangential section showing end of large ray and numerous small uniseriate rays, separated by wood fibres, and occasional wood-parenchyma strands. Fig. 2. — Ulmus americana (American elm) : cross section showing the largest pores in a single row, the small pores in wavy tangential bands. Fig. 3. — Robinia pseudacacia (black locust)-, cross section showing arrange- ment of pores and parenchyma, and very dense wood fibres in late wood; pores in early plugged with tyloses and separated by abundant wood parenchyma and tracheids. Fig. 4. — Toxylon pomiferum (Osage orange) : radial section showing tyloses in vessels; wood-parenchyma strands, tracheids and dense wood fibres; and hetero- geneous ray. Fig. 5. — Gymnocladus dioicus (Kentucky coffee tree): cross section showing comparatively large, thin-walled pores in late wood. Fig. 6. — Gleditsia triacanthos (honey locust): cross section showing minute, thick-walled pores in late wood. Growth ring limited by rather wide zone of wood parenchyma. PLATE III. PLATE IV. DESCRIPTION OF PLATE IV. Fig. 1. — Hicoria ovata (shagbark hickory): cross section showing very thick- walled wood fibres and distinct tangential lines of wood parenchyma; large pores Fig. 2. — Diospyros virginiana (persimmon) : cross section showing rather in- distinct tangential lines of wood parenchyma; pores without tyloses. Fig. 3. — Hicoria pecan (pecan hickory) : tangential section showing very irregular rays, three large calcium-oxalate crystals, and numerous wood-paren- chyma strands. Fig. 4. — Diospyros virginiana : tangential section showing fairly uniform rays in storied arrangement. Crystals visible, but very small. Fig. 5. — The same; radial section showing vessel segments, heterogeneous rays, wood-parenchyma strands, and wood fibres in storied arrangement. Fig. 6. — Juglans nigra (black walnut) : radial section showing rays, large vessel with tyloses, wood-parenchyma strands, chambered-parenchyma cells with crystals, and wood fibres. PLATE V. DESCRIPTION* OF PLATE V. Fig. 1. — Morus rubra (red mulberry): cross section showing arrangement of pores in late wood, width of rays, and presence of tyloses in large pores. Fig. 2. — Fraxinus nigra (black ash) : cross section showing isolated pores in late wood not joined tangentially by wood parenchyma. Outer margin of growth ring composed of thin layer of wood parenchyma. Fig. 3. — Alnus oregona (red alder) : cross section showing aggregate ray and distribution of pores. Fig. 4. — The same: tangential section showing aggregate ray, intermediate uniseriate rays, vessels, wood fibres, and wood-parenchyma strands. Fig. 5. — Betula lenta (sweet or black birch) : cross section showing size and distribution of pores and width of rays. Note wood-parenchyma cells, isolated or in short tangential lines. Fig. 6. — Ostrya virginiana (hornbeam) : cross section showing size and arrangement of pores and distribution of wood-parenchyma cells in inconspicuous tangential lines. PLATE V PLATE VI. DESCRIPTION OF PLATE VI. Fig. 1. — Liquidambar styraciflua (red or sweet gum): cross section showing size and distribution of pores, width of rays, and arrangement of wood fibres in radial rows. Fig. 2. — Liriodendron tulipifera (yellow poplar or tulip-tree): cross section showing size and distribution of pores, and thin layer of wood-parenchyma cells marking outer limit of growth ring. Fig. 3.— Magnolia acuminata (cucumber tree): tangential section showing vessels with scalariform bordered pits, and the small biseriate rays. Fig. 4. — Liriodendron tulipifera: tangential section showing vessels with ordinary bordered pits, and the comparatively large 3-5-seriate rays. Fig. 5. — JSsculus glabra (Ohio buckeye) : cross section showing uniform dis- tribution of pores and rays. Fig. 6. — The same: tangential section showing very fine uniseriate rays, irregularly