WOOD AND FOREST

By WILLIAM NOYES, M.A.

Formerly Assistant Professor of Industrial Arts
Teachers College, Columbia University

NEW YORK CITY

The Manual Arts Press

Peoria, Illinois

COPYRIGHT

WILLIAM NOYES

1912

FIFTH EDITION, 1921

Printed in United States of America

FOREWORD

This book has been prepared as a companion volume to the author's Handwork in Wood.[¹] It is an attempt to collect and arrange in available form useful information, now widely scattered, about our common woods, their sources, growth, properties and uses.

As in the other volume, the credit for the successful completion of the book is to be given to my wife, Anna Gausmann Noyes, who has made the drawings and maps, corrected the text, read the proof, and carried the work thru to its final completion.

Acknowledgments are hereby thankfully made for corrections and suggestions in the text to the following persons:

Mr. A. D. Hopkins, of the United States Department of Agriculture, Bureau of Entomology, for revision of the text relating to Insect Enemies of the Forest, in Chapter VI.

Mr. George G. Hedgcock, of the United States Bureau of Agriculture, Bureau of Plant Industry, for revision of the text relating to the fungal enemies of the forest, in Chapter VI.

Mr. S. T. Dana and Mr. Burnett Barrows, of the United States Department of Agriculture, Forest Service, for revision of Chapters IV, V, VI, VII, and VIII.

Professor Charles R. Richards, formerly Head of the Manual Training Department of Teachers College, my predecessor as lecturer of the course out of which this book has grown.

Professor M. A. Bigelow, Head of the Department of Botany of Teachers College, for revision of Chapter I, on the Structure of Wood.

Mr. Romeyn B. Hough, of Lowville, N. Y., author of American Woods and Handbook of the Trees of the Northern States and Canada, for suggestions in preparing the maps in Chapter III.

The Forest Service, Washington, D. C., for photographs and maps credited to it, and for permission to reprint the key to the identification of woods which appears in Forest Service Bulletin No. 10, Timber, by Filibert Roth.

The Division of Publications, U. S. Department of Agriculture, for permission to copy illustrations in bulletins.

The Macmillan Company, New York, for permission to reproduce Fig. 86, Portion of the Mycelium of Dry Rot, from Timber and Some of its Diseases, by H. M. Ward.

Mrs. Katharine Golden Bitting, of Lafayette, Indiana, for the photograph of the cross-section of a bud, Figure 5.

Finally and not least I hereby acknowledge my obligations to the various writers and publishers whose books and articles I have freely used. As far as possible, appropriate credit is given in the paged references at the end of each chapter.

[Footnote 1:] William Noyes, Handwork in Wood, Peoria, Ill. The Manual Arts Press, 231 pp., $2.

CONTENTS.

GENERAL BIBLIOGRAPHY

Apgar, A. G., Trees of the Northern United States. N. Y.: American Book Co., 224 pp. A small book dealing with the botany of trees, giving descriptions of their essential organs, and particularly valuable for the leaf key to the trees. It should be supplemented by Keeler or Hough's Handbook.

Baterden, J. R., Timber. N. Y.: D. Van Nostrand Co., 1908, 351 pp. A description of the timbers of various countries, discussion of timber defects, timber tests, etc.

Bitting, K. G., The Structure of Wood. Wood Craft, 5: 76, 106, 144, 172, June-Sept., '06. A very scholarly and valuable series of articles on wood structure and growth. Excellent microphotographs.

Britton, Nathaniel Lord, North American Trees. N. Y.: Henry Holt & Co., 1908, 894 pp. A description of all the kinds of trees growing independently of cultivation in North America, north of Mexico, and the West Indies. The standard Botany of trees.

Boulger, G. S., Wood. London: Edward Arnold, 369 pp. A thoro discussion of wood structure, with chapters on the recognition and classification of woods, defects, preservation, uses, tests, supplies, and sources of wood. Good illustrations.

Bruce, E. S., Frost Checks and Wind Shakes. Forestry and Irrigation, 8: 159, April, '02. An original study of the splitting of trees by sudden frost and thaw.

Bruncken, Ernest, North American Forests and Forestry. N. Y.: G. P. Putnam's Sons. 265 pp. A comprehensive survey of American Forestry conditions including the forest industries, fires, taxation, and management. No illustrations.

Busbridge, Harold, The Shrinkage and Warping of Timber. Sci. Amer. Suppl., No. 1500, Oct. 1, 1904. Good photographic illustrations.

Comstock, J. H. and A. B., A Manual for the Study of Insects. Ithaca, N. Y.: Comstock Publishing Co., 701 pp. Valuable for reference in classifying insects injurious to wood.

Curtis, Carleton C., Nature and Development of Plants. N. Y.: Henry Holt & Co., 1907, 471 pp. Chapter III is a very clear and excellent discussion of the structure of the stem of plants (including wood).

Encyclopedia Brittannica, Eleventh Edition, Cambridge: At the University Press. Article: Forests and Forestry, Vol. 10, p. 645. Article: Plants, Anatomy of, Vol. 21, p. 741. Article: Timber Vol. 26, p. 978.

Felt, E. P., The Gypsy and Brown Tail Moths. N. Y. State Museum: Bulletin 103, Entomology, 25. Valuable for colored illustrations as well as for detailed descriptions.

Fernow, B. E., Economics of Forestry. N. Y.: T. Y. Crowell & Co. 1902, quarto 520 pp. A treatment of forests and forestry from the standpoint of economics, including a comprehensive exposition of the forester's art, with chapters on forest conditions, silviculture, forest policies, and methods of business conduct, with a bibliography.

Fernow, B. E., Report upon the Forestry Investigation of the U. S. Department of Agriculture, 1887-1898. Fifty-fifth Congress, House of Representatives, Document No. 181. Quarto, 401 pp. A review of forests and forestry in the U. S., of forest policies of European nations, particularly of Germany, of the principles of silviculture, of a discussion of forest influences, and a section on timber physics.

Harwood, W. S., The New Earth. N. Y.: The Macmillan Co., 1906. 378 pp. A recital of the triumphs of modern agriculture. Chap. X on modern forestry, describes what has been done in different states in conservative lumbering.

Hough, Romeyn B., American Woods. Lowville, N. Y.: The author. An invaluable collection in eleven volumes (boxes) of sections of 275 species of American woods. There are three sections of each species, cross, radial, and tangential, mounted in cardboard panels. Accompanied by a list of descriptions and analytical keys.

Hough, Romeyn B., Handbook of the Trees of the Northern States and Canada. Lowville, N. Y.: The author. 470 pp. A unique, elegant, and sumptuously illustrated book, with photographs of tree, trunk, leaf, fruit, bud, and sometimes wood, a map of the habitat of each species, and a full and careful description of tree and wood. Intended for botanists, foresters and lumbermen.

Johnson, J. B., The Materials of Construction. N. Y.: John Wiley & Sons. 1898. 775 pp. Chapter XIII is identical with Forestry Bulletin X, Roth's Timber.

Keeler, Harriet, Our Native Trees. N. Y.: Scribner's. 1900. 533 pp. A very attractive and popular book showing great familiarity with the common trees and love of them. Numerous photographs and drawings.

Lounsberry, Alice, A Guide to the Trees. N. Y.: Frederick A. Stokes Co. 313 pp. A popular description of some 200 common trees, with plentiful illustrations.

Pinchot, Gifford, A Primer of Forestry. Parts I and II, U. S. Dept. of Agric. For. Serv. Bull. No. 24. 88 pp. and 88 pp. A concise, clear, and fully illustrated little manual of forestry conditions, forest enemies, forestry principles and practice abroad and in the U. S.

Pinchot, Gifford, The Adirondack Spruce. N. Y.: G. P. Putnam's Sons. A technical account of the author's investigations on a forest estate in Northern New York.

Price, O. W., Saving the Southern Forests. World's Work, 5: 3207, March, '03. A plea for conservative lumbering; excellent illustrations.

Record, Samuel J., Characterization of the Grain and Texture of Wood. Woodcraft, 15: 3, June, 1911.

Roth, Filibert, A First Book of Forestry. Boston: Ginn & Co. 291 pp. A book for young people, giving in an interesting form many valuable facts about American forests and their care and use. It includes a leaf key to the trees.

Sargent, Charles Sprague, Forest Trees of North America. U. S. 10th Census, Vol. 9. Quarto, 612 pp. Part I deals with the distribution of the forests, and gives a catalog and description of the forest trees of North America, exclusive of Mexico. Part II. Tables of properties of the woods of the U. S. Part III. The economic aspects of the forests of the U. S. considered geographically, and maps showing distributions and densities. Exceedingly valuable.

Sargent, Charles Sprague, Jesup Collection, The Woods of the U. S. N. Y.: D. Appleton & Co., 203 pp. A detailed description of the Jesup Collection of North American Woods in the American Museum of Natural History, N. Y. City, with valuable tables as to strength, elasticity, hardness, weight, etc. Condensed from Vol. IX of 10th U. S. Census.

Sargent, Charles Sprague, Manual of the Trees of North America. Boston: Houghton, Mifflin & Co. 826 pp. A compact mine of information, with some errors, about the known trees of North America and their woods, summarized from Sargent's larger work, "The Silva of North America." (See below.)

Sargent, Charles Sprague, The Silva of North America. Boston: Houghton, Mifflin Co. A monumental and sumptuous work of 14 quarto volumes, describing in great detail all the known trees of North America and their woods, with beautiful line drawings of leaves and fruits.

Shaler, Nathaniel S., The United States of America. Vol. 1, pp. 485-517. N. Y.: D. Appleton & Co. Chapter IX is a popular description of American forests and the Lumber Industry.

Snow, Chas. Henry, The Principal Species of Wood. N. Y.: John Wiley & Sons. 203 pp. Descriptions and data regarding the economically important varieties of wood, with excellent photographs of trees and woods.

Strasburger, Noll, Schenck, and Schimper. A Text Book of Botany. N. Y.: Macmillan & Co. 746 pp. Valuable for minute information about the morphology of wood.

U. S. Tenth Census, Vol. IX. See Sargent.

U. S. Department of Agriculture, Forest Service Bulletins. The character of these government pamphlets is well indicated by their titles. No. 10 is an exceedingly valuable summary of the facts about the structure and properties of wood, contains the best available key to identification of common American woods (not trees) and a concise description of each. It is incorporated, as Chap. XIII, in Johnson's, "The Materials for Construction." N. Y.: John Wiley & Sons. Nos. 13 and 22 are large monographs containing much valuable information.

No. 10. Filibert Roth, Timber.

No. 13. Charles Mohr, The Timber Pines of the Southern United States.

No. 15. Frederick V. Coville, Forest Growth and Sheep Grazing in the Cascade Mountains of Oregon.

No. 16. Filibert Roth, Forestry Conditions in Wisconsin.

No. 17. George B. Sudworth, Check List of the Forest Trees of the United States, 1898.

No. 18. Charles A. Keffer, Experimental Tree Planting on the Plains.

No. 22. V. M. Spalding and F. H. Chittenden, The White Pine.

No. 24. Gifford Pinchot, A Primer of Forestry.

No. 26. Henry S. Graves, Practical Forestry in the Adirondacks.

No. 41. Herman von Schrenck, Seasoning of Timber.

No. 45. Harold B. Kempton, The Planting of White Pine in New England.

No. 52. Royal S. Kellogg, Forest Planting in Western Kansas.

No. 61. Terms Used in Forestry and Logging.

No. 65. George L. Clothier, Advice for Forest Planters in Oklahoma and Adjacent Regions.

No. 74. R. S. Kellogg and H. M. Hale, Forest Products of the U. S., 1905.

U. S. Department of Agriculture, Forest Service Circulars.

No. 3. George William Hill, Publications for Sale.

No. 25. Gifford Pinchot, The Lumberman and the Forester.

No. 26. H. M. Suter, Forest Fires in the Adirondacks in 1903.

No. 36. The Forest Service: What it is, and how it deals with Forest Problems. Also Classified List of Publications and Guide to Their Contents.

No. 37. Forest Planting in the Sand Hill Region of Nebraska.

No. 40. H. B. Holroyd, The Utilization of Tupelo.

No. 41. S. N. Spring, Forest Planting on Coal Lands in Western Pennsylvania.

No. 45. Frank G. Miller, Forest Planting in Eastern Nebraska.

No. 81. R. S. Kellogg, Forest Planting in Illinois.

No. 97. R. S. Kellogg, Timber Supply of the United States.

No. 153. A. H. Pierson, Exports and Imports of Forest Products, 1907.

U. S. Department of Agriculture Year Books for:

1896. Filibert Roth, The Uses of Wood.

1898, p. 181. Gifford Pinchot, Notes on some Forest Problems.

1899, p. 415. Henry S. Graves, The Practice of Forestry by Private Owners.

1900, p. 199. Hermann von Schrenck, Fungous Diseases of Forest Trees.

1902, p. 145. William L. Hall, Forest Extension in the Middle West.

1902, p. 265. A. D. Hopkins, Some of the Principal Insect Enemies of Coniferous Forests in the United States.

1902, p. 309. Overton, W. Price, Influence of Forestry on the Lumber Supply.

1903, p. 279. James W. Toumey, The Relation of Forests to Stream Flow.

1903, p. 313. A. D. Hopkins, Insect Injuries to Hardwood Forest Trees.

1904, p. 133. E. A. Sterling, The Attitude of Lumbermen toward Forest Fires.

1904, p. 381. A. D. Hopkins, Insect Injuries to Forest Products.

1905, p. 455. Henry Grinell, Prolonging the Life of Telephone Poles.

1905, p. 483. J. Grivin Peters, Waste in Logging Southern Yellow Pine.

1905, p. 636. Quincy R. Craft, Progress of Forestry in 1905.

1907, p 277. Raphael Zon and E. H. Clapp, Cutting Timber in the National Forests.

U. S. Department of Agriculture, Division of Entomology Bulletins:

No. 11. n. s. L. O. Howard, The Gypsy Moth in America.

No. 28. A. D. Hopkins, Insect Enemies of the Spruce in the Northeast.

No. 32. n. s. A. D. Hopkins, Insect Enemies of the Pine in the Black Hills Forest Reserve.

No. 48. A. D. Hopkins, Catalog of Exhibits of Insect Enemies of Forest and Forest Products at the Louisiana Purchase Exposition, St. Louis, Mo., 1904.

No. 56. A. D. Hopkins, The Black Hills Beetle.

No. 58. Part 1, A. D. Hopkins, The Locust Borer.

No. 58. Part II, J. L. Webb, The Western Pine Destroying Bark Beetle.

U. S. Department of Agriculture, Bureau of Plant Industry, Bulletins:

No. 32. Herman von Schrenck, A Disease of the White Ash Caused by Polyporus Fraxinophilus, 1903.

No. 36. Hermann von Schrenck, The "Bluing" and "Red Rot" of the Western Yellow Pine, 1903.

Report of the Commissioner of Corporations on the Lumber Industry, Part I, Standing Timber, February, 1911. The latest and most reliable investigation into the amount and ownership of the forests of the United States.

Ward, H. Marshall, Timber and some of its Diseases. London: Macmillan & Co., 295 pp. An English book that needs supplementing by information on American wood diseases, such as is included in the list of government publications given herewith. The book includes a description of the character, structure, properties, varieties, and classification of timbers.

Chapter I.

THE STRUCTURE OF WOOD.

When it is remembered that the suitability of wood for a particular purpose depends most of all upon its internal structure, it is plain that the woodworker should know the essential characteristics of that structure. While his main interest in wood is as lumber, dead material to be used in woodworking, he can properly understand its structure only by knowing something of it as a live, growing organism. To facilitate this, a knowledge of its position in the plant world is helpful.

All the useful woods are to be found in the highest sub-kingdom of the plant world, the flowering plants or Phanerogamia of the botanist. These flowering plants are to be classified as follows:

Under the division of naked-seeded plants (gymnosperms), practically the only valuable timber-bearing plants are the needle-leaved trees or the conifers, including such trees as the pines, cedars, spruces, firs, etc. Their wood grows rapidly in concentric annual rings, like that of the broad-leaved trees; is easily worked, and is more widely used than the wood of any other class of trees.

Of fruit-bearing trees (angiosperms), there are two classes, those that have one seed-leaf as they germinate, and those that have two seed-leaves.

The one seed-leaf plants (monocotyledons) include the grasses, lilies, bananas, palms, etc. Of these there are only a few that reach the dimensions of trees. They are strikingly distinguished by the structure of their stems. They have no cambium layer and no distinct bark and pith; they have unbranched stems, which as a rule do not increase in diameter after the first stages of growth, but grow only terminally. Instead of having concentric annual rings and thus growing larger year by year, the woody tissue grows here and there thru the stem, but mostly crowded together toward the outer surfaces. Even where there is radial growth, as in yucca, the structure is not in annual rings, but irregular. These one seed-leaf trees (monocotyledons) are not of much economic value as lumber, being used chiefly "in the round," and to some extent for veneers and inlays; e. g., cocoanut-palm and porcupine wood are so used.

The most useful of the monocotyledons, or endogens, ("inside growers," as they are sometimes called,) are the bamboos, which are giant members of the group of grasses, Fig. 1. They grow in dense forests, some varieties often 70 feet high and 6 inches in diameter, shooting up their entire height in a single season. Bamboo is very highly valued in the Orient, where it is used for masts, for house rafters, and other building purposes, for gutters and water-pipes and in countless other ways. It is twice as strong as any of our woods.

Under the fruit-bearing trees (angiosperms), timber trees are chiefly found among those that have two seed-leaves (the dicotyledons) and include the great mass of broad-leaved or deciduous trees such as chestnut, oak, ash and maple. It is to these and to the conifers that our principal attention will be given, since they constitute the bulk of the wood in common use.

The timber-bearing trees, then, are the:

(1) Conifers, the needle-leaved, naked-seeded trees, such as pine, cedar, etc. Fig. 45, [p. 199].

(2) Endogens, which have one seed-leaf, such as bamboos, Fig. 1.

(3) Broad-leaved trees, having two seed-leaves, such as oak, beech, and elm. Fig. 48, [p. 203].

The common classifications of trees are quite inaccurate. Many of the so-called deciduous (Latin, deciduus, falling off) trees are evergreen, such as holly, and, in the south, live oak, magnolia and cherry. So, too, some of the alleged "evergreens," like bald cypress and tamarack, shed their leaves annually.

Fig. 1. A Bamboo Grove, Kioto, Japan.

Fig. 2. Ginko Leaf.

Not all of the "conifers" bear cones. For example, the juniper bears a berry. The ginko, Fig. 2, tho classed among the "conifers," the "evergreens," and the "needle-leaf" trees, bears no cones, has broad leaves and is deciduous. It has an especial interest as being the sole survivor of many species which grew abundantly in the carboniferous age.

Also, the terms used by lumbermen, "hard woods" for broad-leaved trees and "soft woods" for conifers, are still less exact, for the wood of some broad-leaved trees, as bass and poplar, is much softer than that of some conifers, as Georgia pine and lignum vitae.

Another classification commonly made is that of "endogens" (inside growers) including bamboos, palms, etc., and exogens (outside growers) which would include both conifers and broad-leaved trees.

One reason why so many classifications have come into use is that none of them is quite accurate. A better one will be explained later. See [p. 23].

As in the study of all woods three sections are made, it is well at the outset to understand clearly what these are.

The sections of a tree made for its study are (Fig. 3):

(1) Transverse, a plane at right angles to the organic axis.

(2) Radial, a longitudinal plane, including the organic axis.

Fig. 3.

(3) Tangential, a longitudinal plane not including the organic axis.

If a transverse section of the trunk of a conifer or of a broad-leaved tree is made, it is to be noted that it consists of several distinct parts. See Fig. 4. These, beginning at the outside, are:

• (1) Rind or bark
  • (a) Cortex
  • (b) Bast
• (2) Cambium
• (3) Wood
  • (a) Sap-wood
  • (b) Heart-wood
• (4) Pith.

Fig. 4. Diagram of Cross-section of Three Year Old Stem of Basswood.

(1) The rind or bark is made up of two layers, the outer of which, the "cortex," is corky and usually scales or pulls off easily; while the inner one is a fibrous coat called "bast" or "phloem." Together they form a cone, widest, thickest, and roughest at the base and becoming narrower toward the top of the tree. The cortex or outer bark serves to protect the stem of the tree from extremes of heat and cold, from atmospheric changes, and from the browsing of animals. It is made up of a tough water-proof layer of cork which has taken the place of the tender skin or "epidermis" of the twig. Because it is water-proof the outside tissue is cut off from the water supply of the tree, and so dries up and peels off, a mass of dead matter. The cork and the dead stuff together are called the bark. As we shall see later, the cork grows from the inside, being formed in the inner layers of the cortex, the outer layers of dry bark being thus successively cut off.

The characteristics of the tree bark are due to the positions and kinds of tissue of these new layers of cork. Each tree has its own kind of bark, and the bark of some is so characteristic as to make the tree easily recognizable.

Bark may be classified according to formation and method of separation, as scale bark, which detaches from the tree in plates, as in the willows; membraneous bark, which comes off in ribbons and films, as in the birches; fibrous bark, which is in the form of stiff threads, as in the grape vine; and fissured bark, which breaks up in longitudinal fissures, showing ridges, grooves and broad, angular patches, as in oak, chestnut and locust. The last is the commonest form of bark.

The bark of certain kinds of trees, as cherry and birch, has peculiar markings which consist of oblong raised spots or marks, especially on the young branches. These are called lenticels (Latin lenticula, freckle), and have two purposes: they admit air to the internal tissues, as it were for breathing, and they also emit water vapor. These lenticels are to be found on all trees, even where the bark is very thick, as old oaks and chestnuts, but in these the lenticels are in the bottoms of the deep cracks. There is a great difference in the inflammability of bark, some, like that of the big trees of California, Fig. 54, [p. 208], which is often two feet thick, being practically incombustible, and hence serving to protect the tree; while some bark, as canoe birch, is laden with an oil which burns furiously. It therefore makes admirable kindling for camp fires, even in wet weather.

Inside the cork is the "phloem" or "bast," which, by the way, gives its name to the bass tree, the inner bark of which is very tough and fibrous and therefore used for mat and rope making. In a living tree, the bast fibers serve to conduct the nourishment which has been made in the leaves down thru the stem to the growing parts.

(2) The cambium. Inside of the rind and between it and the wood, there is, on living trees, a slimy coat called cambium (Med. Latin, exchange). This is the living, growing part of the stem, familiar to all who have peeled it as the sticky, slimy coat between the bark and the wood of a twig. This is what constitutes the fragrant, mucilaginous inner part of the bark of slippery elm. Cambium is a tissue of young and growing cells, in which the new cells are formed, the inner ones forming the wood and the outer ones the bark.

Fig. 5. Young Stem, Magnified 18½ Diameters, Showing Primary and Secondary Bundles. By Courtesy of Mrs. Katharine Golden Bitting.

E, epidermis, the single outside layer of cells.

C, cortex, the region outside of the bundles.

HB, hard bast, the black, irregular ring protecting the soft bast.

SB, soft bast, the light, crescent-shaped parts.

Ca, cambium, the line between the soft bast and the wood.

W, wood, segments showing pores.

MR, medullary rays, lines between the bundles connecting the pith and the cortex.

MS, medullary sheath, the dark, irregular ring just inside the bundles.

P, pith, the central mass of cells.

In order to understand the cambium and its function, consider its appearance in a bud, Fig. 5. A cross-section of the bud of a growing stem examined under the microscope, looks like a delicate mesh of thin membrane, filled in with a viscid semi-fluid substance which is called "protoplasm" (Greek, protos, first; plasma, form). These meshes were first called "cells" by Robert Hooke, in 1667, because of their resemblance to the chambers of a honeycomb. The walls of these "cells" are their most prominent feature and, when first studied, were supposed to be the essential part; but later the slimy, colorless substance which filled the cells was found to be the essential part. This slimy substance, called protoplasm, constitutes the primal stuff of all living things. The cell walls themselves are formed from it. These young cells, at the apex of a stem, are all alike, very small, filled with protoplasm, and as yet, unaltered. They form embryonic tissue, i.e. one which will change. One change to which an cell filled with protoplasm is liable is division into two, a new partition wall forming within it. This is the way plant cells increase.

In young plant cells, the whole cavity of the chamber is filled with protoplasm, but as the cells grow older and larger, the protoplasm develops into different parts, one part forming the cell wall and in many cases leaving cavities within the cell, which become filled with sap. The substance of the cell wall is called cellulose (cotton and flax fibers consist of almost pure cellulose). At first it has no definite structure, but as growth goes on, it may become thickened in layers, or gummy, or hardened into lignin (wood), according to the function to be performed. Where there are a group of similar cells performing the same functions, the group is called a tissue or, if large enough, a tissue system.

When cells are changed into new forms, or "differentiated," as it is called, they become permanent tissues. These permanent tissues of the tree trunk constitute the various parts which we have noticed, viz., the rind, the pith and the wood.

The essentially living part of the tree, it should be remembered, is the protoplasm: where there is protoplasm, there is life and growth. In the stems of the conifers and broad-leaved trees—sometimes together called exogens—this protoplasm is to be found in the buds and in the cambium sheath, and these are the growing parts of the tree. If we followed up the sheath of cambium which envelopes a stem, into a terminal bud, we should find that it passed without break into the protoplasm of the bud.

In the cross-section of a young shoot, we might see around the central pith or medulla, a ring of wedge-shaped patches. These are really bundles of cells running longitudinally from the rudiments of leaves thru the stem to the roots. They are made of protoplasm and are called the "procambium strands," Fig. 6.

Fig. 6. Three Stages in the Development of an Exogenous Stem. P, pith; PB, primary bast; SB, secondary bast; C, cambium; PR, pith ray; PW, primary wood; SW, secondary wood; PS, procambium strands. After Boulger.

In the monocotyledons (endogens) these procambium strands change completely into wood and bast, and so losing all their protoplasmic cambium, become incapable of further growth. This is why palms can grow only lengthwise, or else by forming new fibers more densely in the central mass. But in the conifers and broad-leaved trees, the inner part of each strand becomes wood and the outer part bast (bark). Between these bundles, connecting the pith in the center with the cortex on the outside of the ring of bundles, are parts of the original pith tissue of the stem. They are the primary pith or medullary rays (Latin, medulla, pith). The number of medullary rays depends upon the number of the bundles; and their form, on the width of the bundles, so that they are often large and conspicuous, as in oak, or small and indeed invisible, as in some of the conifers. But they are present in all exogenous woods, and can readily be seen with the microscope. Stretching across these pith rays from the cambium layer in one procambium strand to that in the others, the cambium formation extends, making a complete cylindrical sheath from the bud downward over the whole stem. This is the cambium sheath and is the living, growing part of the stem from which is formed the wood on the inside and the rind (bark) on the outside.

In the first year the wood and the bast are formed directly by the growth and change of the inner and outer cells respectively of the procambium strand, and all such material is called "primary;" but in subsequent years all wood, pith rays, and bast, originate in the cambium, and these growths are called "secondary."

Fig. 7. Sap-wood and Heart-wood, Lignum Vitae.

(3) The wood of most exogens is made up of two parts, a lighter part called the sap-wood or splint-wood or alburnum, and a darker part called the heart-wood or duramen, Fig. 7. Sap-wood is really immature heartwood. The difference in color between them is very marked in some woods, as in lignum vitae and black walnut, and very slight in others, as spruce and bass. Indeed, some species never form a distinct heart-wood, birch (Betula alba) being an example.

In a living tree, sap-wood and heart-wood perform primarily quite different functions. The sap-wood carries the water from the roots to the leaves, stores away starch at least in winter, and in other ways assists the life of the tree. The proportional amount of sapwood varies greatly, often, as in long-leaf pine, constituting 40 per cent. of the stem.

As the sap-wood grows older, its cells become choked so that the sap can no longer flow thru them. It loses its protoplasm and starch and becomes heartwood, in which all cells are dead and serve only the mechanical function of holding up the great weight of the tree and in resisting wind pressures. This is the reason why a tree may become decayed and hollow and yet be alive and bear fruit. In a tree that is actually dead the sap-wood rots first.

Chemical substances infiltrate into the cell walls of heart-wood and hence it has a darker color than the sap-wood. Persimmon turns black, walnut purplish brown, sumac yellow, oak light brown, tulip and poplar yellowish, redwood and cedar brownish red. Many woods, as mahogany and oak, darken under exposure, which shows that the substances producing the color are oxidizable and unstable. Wood dyes are obtained by boiling and distilling such woods as sumach, logwood, red sanders, and fustic. Many woods also acquire distinct odors, as camphor, sandalwood, cedar, cypress, pine and mahogany, indicating the presence of oil.

As a rule heart-wood is more valuable for timber, being harder, heavier, and drier than sap-wood. In woods like hickory and ash, however, which are used for purposes that require pliability, as in baskets, or elasticity as in handles of rakes and hoes, sap-wood is more valuable than heart-wood.

In a transverse section of a conifer, for example Douglas spruce, Fig. 8, the wood is seen to lie in concentric rings, the outer part of the ring being darker in color than the inner part. In reality each of these rings is a section of an irregular hollow cone, each cone enveloping its inner neighbor. Each cone ordinarily constitutes a year's growth, and therefore there is a greater number of them at the base of a tree than higher up. These cones vary greatly in thickness, or, looking at a cross-section, the rings vary in width; in general, those at the center being thicker than those toward the bark. Variations from year to year may also be noticed, showing that the tree was well nourished one year and poorly nourished another year. Rings, however, do not always indicate a year's growth. "False rings" are sometimes formed by a cessation in the growth due to drouth, fire or other accident, followed by renewed growth the same season.

Fig. 8. Section of Douglas Fir, Showing Annual Rings and Knots at Center of Trunk. American Museum of Natural History, N. Y.

In a radial section of a log, Fig. 8, these "rings" appear as a series of parallel lines and if one could examine a long enough log these lines would converge, as would the cut edges in a nest of cones, if they were cut up thru the center, as in Fig. 9.

Fig. 9. Diagram of Radial Section of Log (exaggerated) Showing Annual Cones of Growth.

In a tangential section, the lines appear as broad bands, and since almost no tree grows perfectly straight, these lines are wavy, and give the characteristic pleasing "grain" of wood. Fig. 27, [p. 35]. The annual rings can sometimes be discerned in the bark as well as in the wood, as in corks, which are made of the outer bark of the cork oak, a product of southern Europe and northern Africa. Fig. 10.

Fig. 10. Annual Rings in Bark (cork).

The growth of the wood of exogenous trees takes place thru the ability, already noted, of protoplasmic cells to divide. The cambium cells, which have very thin walls, are rectangular in shape, broader tangentially than radially, and tapering above and below to a chisel edge, Fig. 11. After they have grown somewhat radially, partition walls form across them in the longitudinal, tangential direction, so that in place of one initial cell, there are two daughter cells radially disposed. Each of these small cells grows and re-divides, as in Fig. 12. Finally the innermost cell ceases to divide, and uses its protoplasm to become thick and hard wood. In like manner the outermost cambium cell becomes bast, while the cells between them continue to grow and divide, and so the process goes on. In nearly all stems, there is much more abundant formation of wood than of bast cells. In other words, more cambium cells turn to wood than to bast.

Fig. 11. Diagram Showing Grain of Spruce Highly Magnified. PR, pith rays; BP, bordered pits; Sp W, spring wood; SW, summer wood; CC, overlapping of chisel shaped ends.

Fig. 12. Diagram Showing the Mode of Division of the Cambium Cells. The cambium cell is shaded to distinguish it from the cells derived from it. Note in the last division at the right that the inner daughter cell becomes the cambium cell while the outer cell develops into a bast cell. From Curtis: Nature and Development of Plants.

In the spring when there is comparatively little light and heat, when the roots and leaves are inactive and feeble, and when the bark, split by winter, does not bind very tightly, the inner cambium cells produce radially wide wood cells with relatively thin walls. These constitute the spring wood. But in summer the jacket of bark binds tightly, there is plenty of heat and light, and the leaves and roots are very active, so that the cambium cells produce thicker walled cells, called summer wood. During the winter the trees rest, and no development takes place until spring, when the large thin-walled cells are formed again, making a sharp contrast with those formed at the end of the previous season.

It is only at the tips of the branches that the cambium cells grow much in length; so that if a nail were driven into a tree twenty years old at, say, four feet from the ground, it would still be four feet from the ground one hundred years later.

Looking once more at the cross-section, say, of spruce, the inner portion of each ring is lighter in color and softer in texture than the outer portion. On a radial or tangential section, one's finger nail can easily indent the inner portion of the ring, tho the outer dark part of the ring may be very hard. The inner, light, soft portion of the ring is the part that grows in the spring and early summer, and is called the "spring wood" while the part that grows later in the season is called "summer wood." As the summer wood is hard and heavy, it largely determines the strength and weight of the wood, so that as a rule, the greater the proportion of the summer growth, the better the wood. This can be controlled to some extent by proper forestry methods, as is done in European larch forests, by "underplanting" them with beech.

In a normal tree, the summer growth forms a greater proportion of the wood formed during the period of thriftiest growth, so that in neither youth nor old age, is there so great a proportion of summer wood as in middle age.

It will help to make clear the general structure of wood if one imagines the trunk of a tree to consist of a bundle of rubber tubes crushed together, so that they assume angular shapes and have no spaces between them. If the tubes are laid in concentric layers, first a layer which has thin walls, then successive layers having thicker and thicker walls, then suddenly a layer of thin-walled tubes and increasing again to thick-walled ones and so on, such an arrangement would represent the successive annual "rings" of conifers.

The medullary rays. While most of the elements in wood run longitudinally in the log, it is also to be noted that running at right angles to these and radially to the log, are other groups of cells called pith rays or medullary rays (Latin, medulla, which means pith). These are the large "silver flakes" to be seen in quartered oak, which give it its beautiful and distinctive grain, Fig. 32, [p. 37]. They appear as long, grayish lines on a cross-section, as broad, shining bands on the radial section, and as short, thick lines tapering at each end on the tangential section. In other words, they are like flat, rectangular plates standing on edge and radiating lengthwise from the center of the tree. They vary greatly in size in different woods. In sycamore they are very prominent, Fig. 13. In oak they are often several hundred cells wide (i.e., up and down in the tree). This may amount to an inch or two. They are often twenty cells thick, tapering to one cell at the edge. In oak very many are also small, even microscopic. But in the conifers and also in some of the broad-leaved trees, altho they can be discerned with the naked eye on a split radial surface, still they are all very small. In pine there are some 15,000 of them to a square inch of a tangential section. They are to be found in all exogens. In a cross-section, say of oak, Fig. 14, it can readily be seen that some pith rays begin at the center of the tree and some farther out. Those that start from the pith are formed the first year and are called primary pith rays, while those that begin in a subsequent year, starting at the cambium of that year, are called secondary rays.

Fig. 13. Tangential Section of Sycamore, Magnified 37 Diameters. Note the large size of the pith rays, A, A (end view).

The function of the pith rays is twofold. (1) They transfer formative material from one part of a stem to another, communicating with both wood and bark by means of the simple and bordered pits in them, and (2) they bind the trunk together from pith to bark. On the other hand their presence makes it easier for the wood to split radially.

The substance of which they are composed is "parenchyma" (Greek, beside, to pour), which also constitutes the pith, the rays forming a sort of connecting link between the first and last growth of the tree, as the cambium cells form new wood each year.

Fig. 14 Cross-section of White Oak. The Radiating White Lines are the Pith Rays.

If a cambium cell is opposite to a pith ray, it divides crosswise (transversely) into eight or ten cells one above another, which stretch out radially, retaining their protoplasm, and so continue the pith ray. As the tree grows larger, new, or secondary medullary rays start from the cambium then active, so that every year new rays are formed both thinner and shorter than the primary rays, Fig. 14.

Now suppose that laid among the ordinary thin-walled tubes were quite large tubes, so that one could tell the "ring" not only by the thin walls but by the presence of large tubes. That would represent the ring-porous woods, and the large tubes would be called vessels, or tracheæ. Suppose again that these large tubes were scattered in disorder thru the layers. This arrangement would represent the diffuse-porous woods.

By holding up to the light, thin cross-sections of spruce or pine, Fig. 15, oak or ash, Fig. 16, and bass or maple, Fig. 17, these three quite distinct arrangements in the structure may be distinguished. This fact has led to the classification of woods according to the presence and distribution of "pores," or as they are technically called, "vessels" or "tracheae." By this classification we have:

(1) Non-porous woods, which comprise the conifers, as pine and spruce.

(2) Ring-porous woods, in which the pores appear (in a cross-section) in concentric rings, as in chestnut, ash and elm.

(3) Diffuse-porous woods, in which (in a cross-section) the rings are scattered irregularly thru the wood, as in bass, maple and yellow poplar.

In order to fully understand the structure of wood, it is necessary to examine it still more closely thru the microscope, and since the three classes of wood, non-porous, ring-porous and diffuse-porous, differ considerably in their minute structure, it is well to consider them separately, taking the simplest first.

Fig. 15. Cross-section of Non-porous Wood, White Pine, Full Size (top toward pith).

Non-porous woods. In examining thru the microscope a transverse section of white pine, Fig. 18:

(1) The most noticeable characteristic is the regularity of arrangement of the cells. They are roughly rectangular and arranged in ranks and files.

(2) Another noticeable feature is that they are arranged in belts, the thickness of their walls gradually increasing as the size of the cells diminishes. Then the large thin-walled cells suddenly begin again, and so on. The width of one of these belts is the amount of a single year's growth, the thin-walled cells being those that formed in spring, and the thick-walled ones those that formed in summer, the darker color of the summer wood as well as its greater strength being caused by there being more material in the same volume.

Fig. 16. Cross-section of Ring-porous Wood, White Ash, Full Size (top toward pith).

Fig. 17. Cross-section of Diffuse-porous Wood, Hard Maple, full size (top toward pith).

(3) Running radially (up and down in the picture) directly thru the annual belts or rings are to be seen what looks like fibers. These are the pith or medullary rays. They serve to transfer formative material from one part of the stem to another and to bind the tree together from pith to bark.

(4) Scattered here and there among the regular cells, are to be seen irregular gray or yellow dots which disturb the regularity of the arrangement. These are resin ducts. (See cross-section of white pine, Fig. 18.) They are not cells, but openings between cells, in which the resin, an excretion of the tree, accumulates, oozing out when the tree is injured. At least one function of resin is to protect the tree from attacks of fungi.

Looking now at the radial section, Fig. 18:

(5) The first thing to notice is the straightness of the long cells and their overlapping where they meet endwise, like the ends of two chisels laid together, Fig. 11.

(6) On the walls of the cells can be seen round spots called "pits." These are due to the fact that as the cell grows, the cell walls thicken, except in these small spots, where the walls remain thin and delicate. The pit in a cell wall always coincides with the pit in an adjoining cell, there being only a thin membrane between, so that there is practically free communication of fluids between the two cells. In a cross-section the pit appears as a canal, the length of which depends upon the thickness of the walls. In some cells, the thickening around the pits becomes elevated, forming a border, perforated in the center. Such pits are called bordered pits. These pits, both simple and bordered, are waterways between the different cells. They are helps in carrying the sap up the tree.

(7) The pith rays are also to be seen running across and interwoven in the other cells. It is to be noticed that they consist of several cells, one above another.

In the tangential section, Fig. 18:

(8) The straightness and overlapping of the cells is to be seen again, and

(9) The numerous ends of the pith rays appear.

In a word, the structure of coniferous wood is very regular and simple, consisting mainly of cells of one sort, the pith rays being comparatively unnoticeable. This uniformity is what makes the wood of conifers technically valuable.

Fig. 18.

Fig. 19. Isolated Fibers and Cells. a, four cells of wood parenchyma; b, two cells from a pith ray; c, a single cell or joint of a vessel, the openings, x, x, leading into its upper and lower neighbors; d, tracheid; e, wood fiber proper. After Roth.

The cells of conifers are called tracheids, meaning "like tracheæ." They are cells in which the end walls persist, that is, are not absorbed and broken down when they meet end to end. In other words, conifers do not have continuous pores or vessels or "tracheæ," and hence are called "non-porous" woods.

But in other woods, the ends of some cells which meet endwise are absorbed, thus forming a continuous series of elements which constitute an open tube. Such tubes are known as pores, or vessels, or "tracheæ," and sometimes extend thru the whole stem. Besides this marked difference between the porous and non-porous woods, the porous woods are also distinguished by the fact that instead of being made up, like the conifers of cells of practically only one kind, namely tracheids, they are composed of several varieties of cells. Besides the tracheae and tracheids already noted are such cells as "wood fiber," "fibrous cells," and "parenchyma." Fig. 19. Wood fiber proper has much thickened lignified walls and no pits, and its main function is mechanical support. Fibrous cells are like the wood fibers except that they retain their protoplasm. Parenchyma is composed of vertical groups of short cells, the end ones of each group tapering to a point, and each group originates from the transverse division of one cambium cell. They are commonly grouped around the vessels (tracheæ). Parenchyma constitutes the pith rays and other similar fibers, retains its protoplasm, and becomes filled with starch in autumn.

The most common type of structure among the broad-leaved trees contains tracheæ, trachæids, woody fiber, fibrous cells and parenchyma. Examples are poplars, birch, walnut, linden and locust. In some, as ash, the tracheids are wanting; apple and maple have no woody fiber, and oak and plum no fibrous cells.

This recital is enough to show that the wood of the broad-leaved trees is much more complex in structure than that of the conifers. It is by means of the number and distribution of these elements that particular woods are identified microscopically. See [p. 289].

Fig. 20.

Ring-porous woods. Looking thru the microscope at a cross-section of ash, a ring-porous wood, Fig. 20:

• (1) The large round or oval pores or vessels grouped mostly in the spring wood first attract attention. Smaller ones, but still quite distinct, are to be seen scattered all thru the wood. It is by the number and distribution of these pores that the different oak woods are distinguished, those in white oak being smaller and more numerous, while in red oak they are fewer and larger. It is evident that the greater their share in the volume, the lighter in weight and the weaker will be the wood. In a magnified cross-section of some woods, as black locust, white elm and chestnut, see [Chap. III], beautiful patterns are to be seen composed of these pores. It is because of the size of these pores and their great number that chestnut is so weak.
  
• (2) The summer wood is also distinguishable by the fact that, as with the conifers, its cells are smaller and its cell walls thicker than those of the spring wood. The summer wood appears only as a narrow, dark line along the largest pores in each ring.
  
• (3) The lines of the pith rays are very plain in some woods, as in oak. [No. 47], Chap. III.
  
• (4) The irregular arrangement and
  
• (5) Complex structure are evident, and these are due to the fact that the wood substance consists of a number of different elements and not one (tracheids) as in the conifers.

Looking at the radial section, Fig. 20:

• (6) If the piece is oak, the great size of the medullary rays is most noticeable. Fig. 32, [p. 37]. They are often an inch or more wide; that is, high, as they grow in the tree. In ash they are plain, seen thru the microscope, but are not prominent.
  
• (7) The interweaving of the different fibers and the variety of their forms show the structure as being very complex.
  

In the tangential section, Fig. 20:

• (8) The pattern of the grain is seen to be marked not so much by the denseness of the summer wood as by the presence of the vessels (pores).
  
• (9) The ends of the pith rays are also clear.

In diffuse porous woods, the main features to be noticed are: In the transverse section, Fig. 21:

• (1) The irregularity with which the pores are scattered,
  
• (2) The fine line of dense cells which mark the end of the year's growth,
  
• (3) The radiating pith rays,
  
• (4) The irregular arrangement and,
  
• (5) The complex structure.

In the radial section, Fig. 21:

• (6) The pith rays are evident. In sycamore, [No. 53], Chap. III, they are quite large.
  
• (7) The interweaving of the fibers is to be noted and also their variety.

In the tangential section, Fig. 21:

• (8) The grain is to be traced only dimly, but the fibers are seen to run in waves around the pith rays.
  
• (9) The pith rays, the ends of which are plainly visible.

Fig. 21.

THE GRAIN OF WOOD.

The term "grain" is used in a variety of meanings which is likely to cause confusion. This confusion may be avoided, at least in part, by distinguishing between grain and texture, using the word grain to refer to the arrangement or direction of the wood elements, and the word texture to refer to their size or quality, so far as these affect the structural character of the wood. Hence such qualifying adjectives as coarse and fine, even and uneven, straight and cross, including spiral, twisted, wavy, curly, mottled, bird's-eye, gnarly, etc., may all be applied to grain to give it definite meaning, while to texture the proper modifying adjectives are coarse and fine, even and uneven.

Usually the word grain means the pattern or "figure" formed by the distinction between the spring wood and the summer wood. If the annual rings are wide, the wood is, in common usage, called "coarse grained," if narrow, "fine grained," so that of two trees of the same species, one may be coarse grained and the other fine grained, depending solely on the accident of fast or slow growth.

The terms coarse grain and fine grain are also frequently used to distinguish such ring-porous woods as have large prominent pores, like chestnut and ash, from those having small or no pores, as cherry and lignum vitae. A better expression in this case would be coarse and fine textured. When such coarse textured woods are stained, the large pores in the spring wood absorb more stain than the smaller elements in the summer wood, and hence the former part appears darker. In the "fine grained" (or better, fine textured,) woods the pores are absent or are small and scattered, and the wood is hard, so that they are capable of taking a high polish. This indicates the meaning of the words coarse and fine in the mind of the cabinet-maker, the reference being primarily to texture.

If the elements of which a wood are composed are of approximately uniform size, it would be said to have a uniform texture, as in white pine, while uniform grain would mean, that the elements, tho of varying sizes, were evenly distributed, as in the diffuse-porous woods.

The term "grain" also refers to the regularity of the wood structure. An ideal tree would be composed of a succession of regular cones, but few trees are truly circular in cross-section and even in those that are circular, the pith is rarely in the center, showing that one side of the tree, usually the south side, is better nourished than the other, Fig. 14, [p. 23].

The normal direction of the fibers of wood is parallel to the axis of the stem in which they grow. Such wood is called "straight-grained," Fig. 22, but there are many deviations from this rule. Whenever the grain of the wood in a board is, in whole or in part, oblique to the sides of the board, it is called "cross-grained." An illustration of this is a bend in the fibers, due to a bend in the whole tree or to the presence of a neighboring knot. This bend makes the board more difficult to plane. In many cases, probably in more cases than not, the wood fibers twist around the tree. (See some of the logs in Fig. 107, [p. 253].) This produces "spiral" or "twisted" grain.

Fig. 22.

Straight Grained Long-leaf Pine (full size).

Fig. 23.

Mahogany, Showing Alternately Twisted Grain (full size).

Often, as in mahogany and sweet gum, the fibers of several layers twist first in one direction and then those of the next few layers twist the other way, Fig. 24. Such wood is peculiarly cross-grained, and is of course hard to plane smooth. But when a piece is smoothly finished the changing reflection of light from the surface gives a beautiful appearance, which can be enhanced by staining and polishing. It constitutes the characteristic "grain" of striped mahogany, Fig. 23. It is rarely found in the inner part of the tree.