Issnol l)c<>i-iiihtr 11, V.Hl. U. S. DEPARTMENT OF AGRICULTURE. 8 D FOREST SERVICE— BULLETIN 102. HENRY S. GRAVES, Forester. ^i'^ THE IDENTIFICATION OF IMPORTANT NORTH AMERICAN OAK WOODS, BASED OxN A STUDY OF THE ANATOMY OF THE SECONDARY WOOD. BY GEORGE B. SUDWORTH, Dendrologist, CLAYTON D. MELL, Assistant Dendrologist, WASHINGTON : GOVERNMENT PRINTING OFFICE. 1911. r Issued December 11, 1911. U. S. DEPARTMENT OF AGRICULTURE, FOREST SERVICE — BULLETIN 102. I^u HENRY S. GRAVES, Forester. THE IDENTIFICATION OF IMPORTANT NORTH AMERICAN OAK WOODS, BASED ON A STUDY OF THE ANATOMY OF THE SECONDARY WOOD. ff? ^\r BY GEORGE B. SUDWORTH, Dendrologist, .>A ^K " ' CLAYTON D. MELL, Assistant Dendrologist. WASHINGTON : GOVERNMENT PRINTING OFFICE. 1911. .0 ,ETTER OF TRANSMITTAL. United States Department of Agriculture, Forest Service, Washington, D. C, Augusts, 1911. Sir: I have the honor to transmit lierewith a manuscript entitled "The Identification of Important North American Oak Woods," by George B. Sudworth, Dendrologist, and Clayton D. Mell, Assistant Dendrologist, and to recommend its publication as Bulletin 102 of the Forest Service. Kespectfully, Henry S. Graves, Forester. Hon, James Wilson, Secretary of Agriculture. 2 CONTENTS, Page. Need for means of identifying the various oaky 7 Preparing wood for examination 9 Gross strneture of oak woods 10 Principal parts of the oak stem 10 Sapwood and heartwood 10 A nnual ri ngs of growth 11 Pith 13 Pith rays 13 Minute structures of oak woods 15 Vessels or pores 15 Tracheids 17 Wood fibers 18 Wood-parencliyma fibers 18 Pith-ray cells .• 20 Structural characters used for identification 21 Analytical key for identification of oaks 22 Characteristics of the different oak woods 24 Laurel oak, Quercus laurifolia 24 Gambel oak, Quercus gambelii 25 Pacific post oak, Quercus garryana 26 Valley oak, Quercus lobata 26 Netleaf oak, Quercus reticulata 28 Arizona white oak, Quercus nrizonira 29 Post oak, Quercus vi'mor 29 Swamp white oak, Quercus pJatunokks 30 Emory oak, Quercus emoryi 31 California black oak, Quercus calif or nica 32 "White oak, Quercus alba 33 Bur oak, Quercus macrocarpa 34 Durand oak, Quercus breviloba 35 Willow oak, Quercus phellos '. 35 Overcup oak, Quercus lyraia 37 Cow oak, Quercus michauxii 37 Chestnut oak, Quercus prinus 38 Chinquapin oak, Quercus acuviinata 39 Shingle oak, Quercus imbricaria 41 Water oak, Quercus nigra 41 Turkey oak, Quercus catesbxi 42 Spanish oak, Quercus digitata 43 Blackjack oak, Quercus marilandica 44 Scarlet oak, Quercus coccinea 45 Bluejack oak, Quercus brevifolia 46 Pin oak, Quercus palustris 46 Texan oak, Quercus texana 48 Yellow oak, Quercus velutina 48 3 4 CONTENTS. Characlerislics of the dift'erout, oak vvooda — Oonliiiued. Page. Red oak, Quercus rubra 49 California live oak, Quercus agri/olia 51 Highland live oak, Quercus wislizeni 51 Canyon live oak, Quercus chrysolepis 53 Blue oak, Quercus douglasii 53 Tanbark oak, Quercus densijlora 54 Live oak, Quercus virgiidana 55 ILLUSTRATIONS. 'I'EXT FKJUKK.s. Page. Fig. 1. Chestnut oak, transverse section of 11 2. Blue oak, transverse section of 12 3. Spanish oak, tangential section of . 14 4. Blackjack oak, radial section of 14 5. Vessel segment 16 6. Longitudinal section of portions of two wood lilxMv 16 7. Tracheid showing bordered pits 16 8. Wood fil)ers 19 9. Wood-parenchyma fiber 19 10. Crystalline masses filling cell cavities 19 11. Laurel oak, transverse section of 25 12. Gambel oak, transverse section of 25 13. Pacific post oak 27 14. Valley oak 27 15. Netleaf oak 28 16. Arizona white oak 28 17. Post oak 30 18. Swamp white oak 31 19. Swamp white oak 31 20. Emory oak 32 21 . California black oak 32 22. White oak 33 23. Bur oak 34 24. Bur oak 34 25. Durand oak 36 26. Willow oak 36 27. Overcup oak 38 28. Cow oak 38 29. Chestnut oak 39 30. Chinquapin oak 40 31. Chinquapin oak 40 32. Shingle oak 42 33. Water oak 42 34 . Turkey oak *. 43 35. Spanish oak 43 36. Blackjack oak 45 37. Scarlet oak 45 38. Bluejack oak 47 39. Pin oak 47 40. Texan oak 49 41. Yellow oak 49 42. Red oak 50 43. California live oak 5u 44. Highland oak 52 45. Canyon live oak 52 46. Rock oak 54 47. California tanbark oak 54 48. Live oak 55 5 THE IDENTIFICATION OF IMPORTANT NORTH AMERICAN OAK WOODS. NEED FOR MEANS OF IDENTIFYING THE VARIOUS OAKS. This bulletin, the first of a series dealing with the distinguishing characters of North American woods (exclusive of Mexico), is pre- pared as an aid in the identification of the principal oaks, which have received first consideration because they are so widely useful. Other groups of woods are to be taken up in order of their commer- cial importance. While this work is designed for the assistance of all students of woods, special effort has been made to render it helpful to manu- facturers of lumber, architects, builders, and other wood users. It is felt, however, that wood users are likely to derive the greatest assistance from the illustrations, by comparing them with the woods to be identified, rather than by trying to use the key, which is intended mainly for trained students. With the conviction that a very large number of wood users can be helped to recognize at least a great many woods, the endeavor has been to present for each wood all available simple characters, carefully combined with such of the less easily observed, finer distinctions as the ordinary student can reason- ably be expected to master. The wood user's need of a reliable means of recognizing commercial woods has become greatly emphasized in recent years because of the enormous demand for standard kinds and species of woods. This increased use is necessitating, in some cases, the substitution of similar or entirely different woods for many of the well-known and long-used ones, the supplies of which no longer meet the demand. Some of the substitutes offered are as good as the standard timbers, while others are inferior to them. However this may be, the fre- quent discovery by consumers that they have not received the woods ordered has led to a great many difficulties and to serious contro- versies involving expensive lawsuits. In many instances manu- facturers believe that in substituting, for example, the woods of several different species of the white oaks for that of the true white oak (Quercus alba) they are doing no injustice to purchasers, and this belief is reasonably supported by facts. Much depends upon the 7 8 TDENTIFTCATION OF NORTH AMERICAN OAK WOODS. use made of the timber. No one could deny that for some purposes the woods of cow oak (Quercus micJiauxii), overcup oak (Q. lyrata), post oak (Q. minor), bur oak (Q. macrocarpa), swamp wliite oak {Q. platanoides) are as good as that of white oak. But the substitution, for example, of the somewhat similar black and red oaks for true wliite oak is less easily defended, because these substitutes are very different in quality from any of the white-oak woods. With the numerous oaks, therefore, as with many other woods the consumer has occasion to distinguish, such superficial characters as color, feel, odor, hardness, weight, etc., can not be depended upon alone as distinctive, because they vary not only with the age of the tree but also according to the soil in which the tree grew and the season and manner of cutting. The butt log differs from the top log, the heartwood from the sapwood, and the wood of a rapidly grown tree fi'om that of a less rapidly grown one of the same species. Wliile the practical woodworker recognizes the woods with which constant work has made him familiar, his knowledge of other woods is necessarily limited. Confronted with the necessity of distin- guishing the few oak woods he knows from a larger number of differ- ent species, the characters he has long and safely relied upon are often insufficient because they may be common to the wood of some of the oaks with which he is unfamiliar. Thus a carefully selected, well-seasoned piece of water oak (Q. nigra) may be so similar in color and general appearance to some grades of white oak as to deceive not a few unacquainted with the structural characteristics of all our oaks. Another difficulty that may be encountered by one who depends entirely upon an empirical knowledge of woods is to prove his con- victions regarding the identity of a wood. For want of exact knowl- edge of the anatomical characteristics of the wood in question, he can only insist upon liis opinion. It happens in actual practice that one inspector passes as white oak a shipment composed of white oak, black oak, and red oak, and his judgment is challenged by another inspector, yet in such an event neither is able to do more than assert his opinion. It must not be understood that a study of the structural characters of woods always renders identification easy. It is sometimes ex- tremely difficult to find characters that distinguish the woods of closely related trees, which may be abundantly distinct in their flowers, fruit, and foliage. It is comparatively easy to point out simple characters wliich distinguish oak from other woods. More- over, it is not difficult to find characters that will separate the white oaks (annual fruiting species) from the black and red oaks (biennial fruiting species). The task, however, of pointing out easily observed distinctions that can be relied upon to separate the woods of different species of wliite oaks, black oaks, and red oaks is difficult, and, in a few instances, impossible without the aid of the high magnifying power PREPARING WOOD. 9 of a compound microscope. This is because some of the minute structural characters, easily demonstrated when greatly magnified, can not be seen under the low magnifying power of a simple pocket lens. However, the need of liigh magnification is confined clfiefly to little-known species, with which the practical wood user is not Ukely to meet. Of the approximately 300 different species of oaks known in the world, about 53, exclusive of varieties and hybrids, occur within the United States. Three or four of these are mere shrubs, while the remainder are small, medium, or large sized trees. The 35 oaks described in tliis publication include all of the commercially useful ones and a number of other species, the woods of wliich ars likely to become more or less useful in the future. The remaining 15 species are excluded from the present treatise because their woods are of inferior quahty or the trees occur in such limited quantities as to be of little or no economic importance. The illustrations accompanying this bulletin were made by out- lining with a pen photographs of enlarged transverse sections * of the wood, and they show the exact appearance of each section as seen under a microscope magnifying the structure 20 times its natural size. The illustrations are so arranged that the pith rays run up and down, and the outside of the annual layer of growth stands toward the top of the page. Structural characters of the wood having the most distinct value for identification are confined principally to transverse sections, in which the size, form, arrangement, and other relations of elements are clearly shown. The greatest aid will be derived, therefore, by a careful comparison of the smoothly cut end of a block with the illustrations. Radial and tangential sections were also studied for the purpose of discovering any distinctions which these views of the wood might ofter. A great many measurements of the fibers of each species, to be seen only in these sections, were taken, and their average length computed. These are shown in Table 1 on page 56. PREPARING WOOD FOR EXAMINATION. In preparing a piece of wood for examination with the pocket lens it is necessary to cut a smooth surface approxunateh' at right angles to the vertical axis of the specimen. If the knife is not sluup the surface of the cut will be rough and show but little of the char- acteristic structure. With a specimen carefully prepared in this way, the observer will be surprised to see how much of detail in the 1 Preparatory to sectioning, small blocks of wood, of about one-half cubic centimeter, were first boiled in water until they were thoroughly saturated and partially softened, after which they were placed in a dilute solution of hydrofluoric acid for about 10 days in order to dissolve out the silicates. After thoroughly washing the blocks in water, microscopic sections, 8 to 12 micro-millimeters thick, were cut from them with a microtome. These sections were then double-stained in safranin an^ Delafields hsemato.xylyi and mounted, in the susual way, in balsam, on glass slides. 7718°— Bull. 102—11 2 10 IDENTIFICATION OF NORTH AMERICAN OAK WOODS. wood stnicture a small pocket lens reveals. By using the most pow- erful form of an aplanatic tiiplet pocket lens a still better view of the structure can be had. GROSS STRUCTURE OF OAK WOODS. PRINCIPAL PARTS OF THE OAK STEM. ^lany are familiar with the prmcipal parts of an oak stem as shown on a freshly cut stump. These parts comprise, first, the bark: sec- ond, the sap wood; third, the heartwood; and fourth, the pith. Throughout the wood of the stem there are more or less distinct and irregularly concentric lings of varying thickness. These are annual lings of growth. Running from the i)ith or center of the stem to the bark are spoke-like lines, which are pith rays. These different tissues afford distinctive features as they appear m close union, and are therefore briefly described below, so that the reader may become familiar with their characters and arrangement as a means of classifying and identifying different species. SAPWOOD AND HEARTWOOD. A transverse section of the stem of an old oak ti-ee shows two dis- tinct zones. The outer portion called sapwood (alburnum) (fig. 1, s. w.) is of a light color and consists of a more or less thick zone immediately beneath the bark (fig. 1, h.); the inner portion kno\vn as heartwood (duramen) is generally darker colored (reddish brown to yellowish brown), forming a much harder and more durable mass. The width of the heartwood increases year by year, but that of the sapwood reniams approxmiately the same, for an inner layer of sap- wood becomes transformed annually into an outer layer of heartwood. This difference between the sapwood and heartwood is always quite evident in hardness and color. The heartwood is lifeless and serves the tree only as a mechanical support, while the sapwood alone is the living part of the tree and the part in which all vital activities take place. The heartwood owes its darker color and its hardness and durability to the infiltration of dark-colored chemical sub- stances, such as gums and resinous substances, which impregnate the cell cavities and frequently fill up the cavities of the wood fibers. The sapwood of the dift'erent species of oaks varies considerably in width; for example, it is thin in red oak and thick in Spanish oak. It varies also in different trees of the same species, depending upon the soil, light, and climatic conditions as well as on the general health of the trees. Although color and thickness of sapwood are sometimes useful characters in distinguishing different woods, fre- quently they can not be depended upon. Moreover, a large })ro})or- GROSS STRUCTURE. 11 tion of the sawed oak timber reaching the markets consists wholly of heartwood. For these reasons the structural characters of the heartwood, not different, however, from those of the sapwood, have been mainly relied uj>on as a basis for classification. ANNUAL RINGS OF GROWTH. All North American oaks exhibit in transverse sections more or less clearly the so-called zones or annual rmgs of growth (fig. 1, a. r.). ■--—■p.r. Fig. 1.— Transverse section of chestnut oak (J^uercus prinus); &.,bark; s. w., sapwood; the darker inner portion is heartwood; a. r., annual ring; p. r., pith ray. Natural size. In rapidly growing trees these layers are distinctly marked, while in those from dry arid regions of the West, wliere the growing season is short, or often restricted to periods of rain, the la3'crs are so narrow that they appear to be absent or at least obscured by the mere suc- cession of inconspicuous rings composed chiefly of pores (fig. 2). The width of the rings varies greatly with the age of the tree, also in ditt'erent parts of the same tree and m different trees of the same species. Trees growing in the open develop larger crowns, and 12 IDENTIFICATION OF NOKTH AMERICAN OAK WOODS. consequently manufacture a greater amount of plant food, than trees in a dense forest. The mcrease m foliage is accompanied by an increase in the rate of diameter growth. It follows, therefore, that trees in the oi)en w^ith plenty of growing space develop wide annual rings, while those in the forest with limited s])ace for crown develo})- ment often form very narrow rings. The number of growth rings shown in a transverse section of an oak, or any other tree grown in a tem])erate climate, in general indi- cates the age of the tree, since normally one ring or layer of growth is added to the thickness of the trinik and its branches each year. There are, however, frequent influences which disturb tliis geneial Fig. 2.— Transverse section of (California) blue oak (Quercus douglasii); h., bark; s. u\, sapwoo'l: the dark inner portion is heartwood; p. r., pith ray. Natural size. regularity, such as drought or the destruction of the leaves by msects during the growing season. The result is a tem])orary cessation of growth, and in such a case trees may again })ut forth a new set of leaves and start growth anew during the same season. This usually results in the formation of another ring of pores (the characteristic growth at the beginning of the season) similar to the normal early wood. This second or newly formed layer is called a "false ring." Annual rings of growth consist of an inner and more porous por- tion known as early wood (fig. 32, e. w.) and an outer and denser portion called late wood (fig. 32, Z. w.). These more or less sharply GKOss strttctuhe. 13 contrasted parts of tlie annual rings are a result of tlie development of a gradually dimishing number of large vessels duiing the latter ])art of the season's growth. The denser portion, therefore, encases the more porous part, or early wood, which contains elements with larger diametei-s and thinner walls. These elements are called vessels, which serve as conducting tissue. The de.nse late wood, which ordinarily forms the greater part of the annual ring, is com- posed largely of closely packed, thick-walled wood fibere wliich give the wood strength, weight, toughness, and elasticity. The wood of slowly grown oaks, and particularly that of old trees, is often exceed- ingly ''brash," because it contains a very large proportion of early (porous) W'Ood. The proportion of late to early wood is usually greater in fast- growing than in slow-growing trees. This is true especially of the wood formed near the base of the stem, where it is denser and heavier than that in any other portion of the tree. There is less early wood formed at the base of the stem than farther up, because growth com- mences nearly a month later at the base. The strongest, densest, and toughest oak timber is that grown in the open, where the full enjoyment of side light })roduces wide rings. PITH. A transveree section of the stem of an oak exhibits a Ught-brown speck in the center commonly known as the pith, wliich is quite small and does not increase in size as the tree growls older. (See center of figs. 1 and 2.) The cells composing the pith are thin walled, usually of uniform diameter, and gradually become emptied of their contents. In some oaks these elements, technically known as parenchyma cells, continue to live for a number of yeare, later becoming lignified and tliickened with age, so that it is often difficult to detect the pith in steins of old trees. In transvei-se section the pith of most oaks is pentagonal in outline. This character is useful in distinguishing oaks as a group from other woods. PITH RAYS. Pith rays constitute the spoke-like lines to be seen more or less conspicuously on the transverse section of the oak stem (figs. 1 and 2, J), r.). They form the so-called "silver gram" w^ell knowTi among caipenters. The large (primaiy) pith rays are merely spokes, as it were, joining the pith and bark. Each spoke is from a few to 25 or more ray cells in width, and from 100 to 600 or more cells in height (lig. 3, p. p.r.). Each succeeding year other rays are formed, which extend from the point where they originate to the peiipheiy of the stem. These are called small (secondaiy) pith rays because 14 rOENTIFICATION OF NORTH AMERICAN OAK WOODS. tlicy started later in tlio life of the tree, but tliey serve the same l)iii1)oses and bear the same rehitionship to other tissue of the stem as the hirge pith rays, except that they do not extend inward to the pith (fig. 3, s. p. r.). The small rays are seldom more than one cell wide, but are from a few to 20 or more cells high. On a radially split surface of oak wood the large pith rays may be seen with the unaided eye as horizontal bands traversing the wood from within outward; the small rays can not be seen with the unaided eye. The presence of two kinds of ra3^s in the woods of all North Ameri- can oaks furnishes another helpful generic distinction. Investiga- FiG. 4. Fig. 3.— Spanish oak (Quercus dlgilata). Tangential section showing large (/>. p. r.) ami small pith rays (.S-. p. r.) magnified about 20 diameters. Fi(i. 4.— Blackjaeli (QwercM* marilandka). Radial section showing pith rays (p. r.) magnified 20 diameters. tions show, however, that the charactei's of the pith rays in oaks are not sufficiently constant to distinguish tlie different species. The number of pith rays is largely dependent upon the age of the tree, and they are most abundant m wood of the first layer of growth. Proceedmg from this toward the bark they gradually dimmish in number per unit area for a certain period of yeai*s, and then agam, later in the hfe of a tree, they commence to increase in number. Moreover, different individuals of the same species show a marked variation in the number of pith rays. With reference to the number of rays for the dilTerent species of oaks, the figures obtained by actual counts are exceedingly variable. Again, the height of the pith rays ill the same individual and in different individuals of the same MINUTE STRUCTURES. 15 Species IS so variable that it can not be accepted as a trustwortliy mark of distinction. As the trees grow older the pith ra^'s gradually mcrease in height. Evergreen oaks, and particularly veiy slow- growing species or those growing on dry arid soil, develop rather lo^y and wide rays, which have blunt ends above and below. This applies particularly to oaks of the Rocky Mountain and Pacific slope regions. The deciduous oaks, growing in rnoist, alluvial soils, develop high and narrow pith rays which have niore or less acute ends above and below. This applies particularly to the eastern oaks (compare figs. 1 and 2). For a difference in comparative width of pith rays in the two arbitrary groups referred to above see figures 1 and 2. MINUTE STRUCTURES OF OAK WOODS. Tlie minute elements which make up the wood of oaks will be described separately, in order to present a clear general view of the part they play in the composition of the wood. Size, shape, relative proportion, and grouping of the elements are more or less charac- teristic in all woods, and a clear idea of these elements can be ob- tained only by a study of the transverse, radial, and tangential sec- tions under a compound microscope. Five different kinds of ele- ments can then be distinguished; namely, vessels, tracheids, wood fibers, wood-parenchyma fibers, and pith-ray cells. VESSELS OR PORES. The vessels differing in size and arrangement may be seen with the unaided eye in a transverse section of the wood of both deciduous and evergreen oaks. These vessels, commonly known as pores, and tech- nically as tracheae, make up chiefly the inner and more porous part of the annual ring of growth. They vary from less than 0.1 to more than 0.6 of a millimeter ^ in diameter and are composed of tube-like segments arranged longitudinally end to end; the cavities of the vessels communicate directly with one another, while the adjoining obliquely formed ends are perforated by horizontal pits (fig. 5a, a.), or are completely absorbed (fig. 5, a.) so that the rows of cells or vessel segments finally form long, continuous tubes. These oblique cross walls (fig. 5, c. w.) between the vessel segments not infrequently have scalariform (ladder-like) perforations (fig. 5a, a.). Individually the segments arc often short and barrel-shaped, though they usually have rather obliquely formed end walls which always face toward the pith rays. The segments in late wood are about twice as long as they are wide, but in the early wood their diameter sometimes exceeds their length. In a longitudinal section of oak wood they appear as minute 1 One millimeter is equal to about one twenty-fifth of an inch. The metric system is used in this work in order to avoid large fractions. 16 IDENTIFICATION OF NORTH AMERICAN OAK WOODS. channels. The vessels which are arranged in radial rows (transverse section) in the late wood have a successively smaller diameter than those formed earlier, and with this gradual diminution in diameter bp.. RsS- fi£ 6, ^'"''fed f^e fo F.i.k ns7 Fig. 5. — Vessel segment showing oblique cross walls (c. w.) completely absorbed at a; b. p., bordered pit. Magnified about 100 diameters. Fig. 5a.^VesseI segment showing oblique cross walls (c. w., partly absorbed); a, scalariform (ladder-like) perforations; 6. p., bordered pits. Magnified 100 diameters. Fig. (5. — Longitudinal section of portions of two wood fibers showing simple pits (s. p.); c. w., cell wall; r. c, cell cavity. Magnified about 100 diameters. (See also fig. 8.) Fig. 6a. — 1. Longitudinal section of a bordered pit (&. p.); t, torus. 2. Surface view of pit; corresponding regions are connected by dotted lines. Magnified about 500 diameters. Fig. 7.— Tracheid showing bordered pits (6. p.). Magnified about 75 diameters. there is generally a corresponding increase in the thickness of the walls of these elements, a factor which adds mechanical support to the tree. The size and arrangement of these small vessels in the late wood also afford, to some extent, distinctive features. MINUTE STEUCTUEES. 17 The side walls of vessels become sculptured or pitted at maturity, and the commonest form of sculpture is the result of small areas in the walls called pits remaining unchanged during the thickening process called lignification. These unthickened portions may be seen with the aid of a microscope in a longitudinal section of oak wood. The pits are of two kinds, simple and bordered. A simple pit is a very small thin portion of the cell wall, forming a short, regular, and radi- ally directed canal within the cell wall (fig. 6, s. j)-)- A bordered pit is formed in a similar manner, but the walls of the canals always make a distinct angle, thus leaving the short canal wide on the outside and narrow toward the center of the cell (fig. 6a, h. p.). Pits are shal- low, depending upon the thickness of the cell walls, while in outline they are elliptical, elongated, or rarely rectangular. In a few cases they are so extended as to form thickened ridges between the pits and appear like the rungs of a ladder; hence the name scalariform markings. This mode of thickening is sometimes seen in the sap- wood of evergreen oaks. After vessels lose their sap and the air in them is rarefied, tyloses (very delicate partition-like walls) begin to form and to block up the cavities, rendering the heartwood impervious, or nearly so, especially in most species of the white oak group, to the entrance of fluids. Tyloses consist of parenchymatous (pith-like) tissue (fig. 4, t.) which has been forced out of the swelling (turgescent) adjacent thin-walled pith-ray cells or wood-parenchyma fibers into the lumina or channels of the vessels. The thin membranes (original, unthickened portions of cell wall) within the bordered pits, which separate the contents of the adjacent parenchyma cells, are ruptured by the swelling of the pith-ray cells. This parenchymatous tissue commences to grow very rapidly and in a short time fills up the cavities of the vessels. Tyloses are particularly abundant in v^ood of oaks belonging to the white oak group, and not infrequently serves to separate the white from the black oaks. TRACHEIDS. Tracheids (fig. 7) are usually found immediately adjoining the ves- sels. They are slight modifications of the wood fibers (described below), and differ from them in having thin walls with numerous more or less narrow and oblique or horizontal bordered pits. These pits occur irrespective of whether the contiguous elements are ves- sels, tracheids, or wood fibers. Tracheids are single fiber-like ele- ments, and are, therefore, easily distinguished, whereas vessels are formed by a fusion of cells placed end to end. In transverse sections it is more difficult to separate them from the very small vessels. The ends of these tracheids are often curved, especially if the tracheid terminates immediately above or below a pith ray. They also have the 7718°— Bull. 102—11 3 18 IDENTIFICATION OF NORTH AMERICAN OAK WOODS. form of barbed books as seen occasionally in the wood of Quercus wislizeni and Q. virginiana. Tracheids are not referred to in the description of different species of oak wood, for the reason that they are not distinctive features. WOOD FIBERS. Wood fibers (fig. 8a) are veiy fine, thread-like cells, which com- pose chiefly the dark, dense outer portion of the annual ring of growth. They resemble the tracheids, though they are longer and sometimes have walls so thick that scarcely any cell cavities (fig. 8a, c. c.) remain. Wood fibers may be divided into two classes: First, those that are unsegmented and either have no pits at all or only a few partially developed simple pits; and second, those that are segmented and have simple pits in their walls. The segmented wood fibers are found very rarely in the wood of oaks, being restricted mainly to the wood of Quercus garryana, here present in an intermediate form of element between wood fibers and wood-parenchyma fibers discussed later. The narrow, thick-walled, and unsegmented wood fibers make up the greater portion of the mass of the wood of oaks (fig. 8). In Quercus lyrata wood fibers with wide cavities and rather thin walls form the greater part of the late wood, which accounts for its light weight and softness. Thick- walled, compactly arranged elements render the wood heavy, as in the case of most evergreen oaks. This is particu- larly true of the live oaks, Quercus chrysolepis and Q. virginiana. The cavities of the wood fibers are widest in Q. cateshsei, Q. lyrata, Q. nigra, and Q. phellos. On this account the wood of these oaks is softer and is worked more easily than that of the other species. The narrowest or thinnest wood fibers are found in Q. minor and Q. platanoides. The average length of wood fibers of all the North American oaks is approximately 1.3 ^ millimeters (about ^V of an inch). The longest fibers are found in the wood of Q. coccinea, while the shortest occur in Q. arizonica and Q. rubra. The ends of some wood fibers are flattened and sometimes even forked and with a saw edge (fig. 8b, a and h). Fibers usually run parallel to one another, but there may be seen in some of the western species a decided interweaving with one another, which produces "cross-grained" wood, difficult to split. WOOD-PARENCHYMA FIBERS. The individual cells of wood-parenchyma fibers resemble the pith- ray cells, ])ut they are grouped in vertical rows instead of horizontal rows (figs. 9 and 10). They predominate in the more porous parts 1 All dimensions of wood elements given in this work are averages not only of a great many different measurements of elements from a large number of samples, but also of elements from different parts of the same specimens. It is advisable, therafore, in attempting to trace down a piece of oak wood carefully to examine slides made from ditTerent parts of a specimen. MTNUTE STRUCTURES. 19 of the annual rings of growth and often closely surround the vessels and tracheids. In the dense late wood, wood-parenchyma fibers form conspicuous, tangentially arranged bands between irregular, ,S p. Fes S - -sp '^' ^ fS- Fig. 8.— Transverse section of wood fibers; p. r. c, pith ray cell; c, crystal of calcium oxalate; w.f., wood fibers; s. p., simple pit. Magnified about 17.5 diameters. Fig. 8a.— Wood fiber showing thick walls (c. «'.), and a small cavity (e. c); s.p., simple pit. Magnified about 150 diameters. Fig. 8b.— a, Wood fiber forked at one end; 6, wood fiber with a saw-toothed edge at one end; «. /)., ol)lique simple pits. Magnified about 103 diameters. Fig. 9.— Wood-parenchyma fiber showing individual cells (c); s. p., simple pits. Magnified about 125 diameters. Fig. 10.— Crystalline masses (idioblasts) completely filling the individual cell cavities; c, crystals of calcium oxalate; s. p., simple pits. Magnified about 125 diameters. compact, radial rcnvs of thick-walled wood libers. On a ])erfectly smooth transverse section of oak wood, having well-defined late wood, these bands of wood-parenchyma fibers can be detected with the 20 IDENTIFICATION OF NORTH AMERICAN OAK WOODS. unaided eye (fig. 15, w. 'p. J.). When greatly internn)ted by wood fibers, the wood-parenchyma bands become indistinct and can be distinguished only by means of a microscope. In late wood these elements are usually round in transverse section, but in early wood, where unequal pressure is exerted upon them by the rapid growth of vessels, they are flattened and their usual shape and arrangement are often greatly disturbed. The size, shape, and niarkmgs of wood-parenchyma fibers in late wood of difi'erent oaks vary but little. The pits are chiefly simple (fig. 9, s. ]).), though occasionally wood-parenchyma cells are found that have bordered pits, as in the case of some evergreen oaks. The abundance, arrange- ment, and the particular relation these elements bear to one another are, however, important in distinguishing the wood of the dift'erent species of oalvs. Wood-parenchyma cells usually contain starch, and also a certain quantity of tannin, but these facts are of little value in identifying the different oaks, since the amount and nature of cell contents depend greatly upon the age of the tree, the time of the year the tree was cut, and the part of the tree from which the wood was taken. Crystals of calcium oxalate (fig. 10, c.) are found in all paren- chymatous tissue of all species of oaks. They are developed smgly in the cells and belong to the tetragonal crystal system. These ciystals are only slightly soluble even in the strongest acids and are very clearly visible under the high power of the microscope both in transverse and longitudinal sections. In pith-ray cells they are often found in rows of from 3 to 6, while in wood-parenchyma fibers they occur in much longer rows, particularly in the early wood, and are technically known as idioblasts (fig. 10). In such cases the whole cell becomes merely a repositoiy for the crystal. Such crystals are especially frecpient in the wood of Quercus arizonica, Q. calijornica, Q. douglasii, Q. emoryi, Q. gamhelii, Q. garryana, Q. lohata, Q. lyrata, Q. reticulata, Q. texana, and Q. virginiana. Individual sam}>les of other oaks are often found, however, that contain as many ciystals as those just named. A careful investigation has sho^\^l that the woods of evergreen oaks, and especially those of the Roclcy Mountain and Pacific coast regions, contain more ciystals than those of the eastern deciduous oaks in general. PITH-RAY CELLS. Pith-ray cells have already been briefly described in c(Hmection with pith rays. They occur in from one to many rows closely packed together, and individually are arranged end to end with their long axes in a radial direction. In a transverse section these radial rows of parenchyma cells can be seen as narrow but more or less distinct STRUCTURAL CHARACTERS. 21 lines; the larger ones (fig. 3, p. p. r.) extending from the pith to the peripheiy of the stem. The width and height (tangential section) of these rays are entirely dependent upon the age of the tree and upon the distance from the pith or peripheiy of tlie stem. In a tangential section the small pith rays are seen in vertical rows of a single cell in width, and from a few to 20 or more cells in height (fig. 3, s. p. r.). Where these cells are m contact with one another or with wood-parenchyma fibers the pits are simple (fig. 8, s. p. in p. r.), but if they lie next to vessels or tracheids the portion of the converging pits in vessel walls is bordered, and that of the ray cells is simple. STRUCTURAL CHARACTERS USED FOR IDENTIFICATION. The technical generic name of oak, Quercus, is derived from the Celtic words quer, meaning "fine," and cuez, "tree," in reference to its highly esteemed qualities. The genus Quercus belongs to the family Fagacese, wdiich contains three other genera, Fagus, Casfanea, and Castanopsis, native to the United States. The oaks are trees and shrubs distributed widely over the northern hemisphere and in parts of Java and South America. The different species vary greatly in the form and character of their leaves, fruit, bark, and general appearance, but there are no such marked constant characters as these present in the woods of oaks by means of which they can be readily distinguished. There is much variation in the appearance of the wood of the different oaks, but the woods of different trees of any particular species may also vary so remarkably in appearance, depending upon the conditions under which the trees grew, that it often requires very careful study to identify them. The woods of the oaks described in this work are classified according to differences in the form and arrangement of the large and small vessels (pores), wood fibers, and wood-parenchyma fibers, also according to the width and outline of the annual rings of growth, and by a comparison of the early and late wood composing each ring. Microscopic characters have been resorted to only when the gross characters are insufficient for identification. A number of the ever- green oaks, native to high, dry plains of the Southwest, have hard wood, and show exceedingly narrow layers of growth and very wide pith rays. A few of our oaks have a very wide natural range of growth, which accounts in a great measure for the variability in the character of their woods. Bur oak, for instance, ranges from Nova Scotia westward to Manitoba and southwestward to Texas. Witliin this range it occurs both in the form of chaparral and as a large tree, and the character of the wood varies greatly with the different situa- tions to which it has become adapted (figs. 23 and 24, p. 34). 22 IDENTIFICATION OF NORTH AMERICAN OAK WOODS. ANALYTICAL KEY FOR THE IDENTIFICATION OF IMPORTANT NORTH AMERICAN OAKS, BASED ON CHARACTERS OF THE SECONDARY WOOD.' A. Marked distinction between early and late wood. 1. Pores abruptly diminishing in size from early to late wood; large pores contain considerable tyloses. WHITE AND WILLOW 0.\KS. Pores in early wood arranged mo.^tly in 1 tangential row or rarely in 2 distinct rows; pore.-i in lale wood half the size of those in early wood, few and scat- tered 1. Quercus laurifolia (p. 24). Pores in early wood arranged in 1 to 3 tangential rows; pores in late wood less than half the size of those in early wood. Pores in late wood 0.05 ^ millimeter or less in diameter and arranged irregu- larly or in single or double radial rows. Pores in late wood mostly forming single radial rows; tangential l)ands of wood-parenchyma fibers conspicuous 2. Quercus gamheUi (p. 25). Pores in late wood mostly forming double radial rows; tangential bands of wood-parenchyma fibers less conspicuous, except in 5. Radial rows of small pores surrounded by v>'ood-parenchyma fibers; these rov.-s becoming wider near the periphery of the annual ring. .3. Quercus gnrryana (p. 2G). Walls of ]V)res in early wood thicker than those in the late woo;l. Crystals of calcium oxalate rare 4. Quercus lobata (p. 26). Walls of pores in earh- wood thinner than those in the late wood. Crystals of calcium oxalate very numerous. Pores in early wood vary from 0.05 to 0.2 millimeter in diameter; tangential bands of wodd-jiarenchyma fibers very wide. 5. Quercus reticulata (p. 28). Pores in early wood vary from 0.2 to 0.3 millimeter in diameter; tangential bands of wood-parenchyma fibers very inconspicuous. 6. Quercus arizonica (p. 29). Pores in late wood more than 1 millimeter in diameter and arranged chiefly in single radial rows. Radial rows of pores extending to periphery of annual rings of growth. Pores in early wood round and from 0.15 to 0.25 millimeter in diameter. 7. Quercus minor (p. 29). Pores in early wood chiefly ellii)tical and 0.2 to 0.3 millimeter in diameter. S. Quercus platanoides (p. 30). Radial rows of pores rarely extending to ])eri])hery of annual rings of growth. 9. Quercus emori/i (p. 31). Pores in late wood very variable and arranged chiefly in double, radial rows. Pores uniformly large and rows invariably extending to the periphery of annual rings of growth 10. Quercus caUfornica (p. 32). Pores very irregular in size and radial rows rarely extending to the periphery of annual rings of growth. ! Sapwood and heartwood, the strictly woodj^ parts of a tree stem, are collec-tively known as secondary wood, a technical name given to mature wood because its formation follows in the order of tlevelopment the growth of tissue known as primary wood, which is intermediate in character between the purely paren- chymatous tissue of ])ith and fully matured wood. The general order of growth in a tree stem is therefore, first, the production of the purely parenchymatous tissue of pith; second, the formation of primary wood; and third, the laying on of secondary wood. Following the production of pith and primary wood comes the formation of the so-called "cambium ring," a generative layer of thin-walled cells, which develops second- ary wood on its inner side and bark on its outer side. 2 See footnote 1, p. 15. ANALYTICAL KEY, 23 Wood-parenchyma fibers in late wood arranged chiefly in conspicuous, double, tangential bands. Tyloses very abundant. Large pith rays about 4 millimeters apart 11. (juercus alba (p. 33). Large pith rays about 6 millimeters apart. 12. Quercus macrocarpa (p. 34). Wood-parenchyma fibers in late wood scattered rather irregularly, occa- sionally in short, parallel, inconspicuous, tangential bands. Pores in early wood arranged chiefly in one row, with broad, conspicuous radial rows of smaller pores. Pores in early wood round or oval 13. Quercus breviloba (p. 35). Pores ia early wood strongly elliptical 14. Quercus phellos (p. 35). Pores in early wood arranged chiefly in 2 to 3 rows and pores in late wood larger than in 13 and 14. Radial rows of pores in late wood unusually wide; heart wood dark brown with lighter-colored sapwood — .15. Quercus lyrata (p. 37). Radial rows of pores in late wood usually narrow^er; heartwood light brown, with darker-colored sapwood.. 16. Quercus michauxii (p. 37). Pores in early wood arranged in 3 to 5 rows. Walls of pores in late wood thin; radial rows of small pores become wider toward periphery of annual rings of growth. . .17. Quercus prinus (p. 38). Walls of pores in late wood thick; radial rows of small pores become narrower toward the periphery of the annual rings of growth. Pores in late wood chiefly in single radial rows. 18. (Quercus acuminata (p. 39); Pores in late wood chiefly in double radial rows. 19. Quercus imbricaria (p. 41). 2. Pores gradually diminishing in size from early to late wood ; large pores contain very little tyloses. BLACK OAKS AND RED OAKS. Pores in early wood arranged chiefly in 1 to 3 rows. Radial rows of small pores usually numerous, double, and somewhat irregular; tangential bands of wood-parenchyma fibers very numerous. 20. Quercus nigra (p. 41). Radial rows of small pores usually single and parallel ; tangential bands of wood-parenchyma fibers few and inconspicuous. Pores in early wood round; wood light brown and strongly tinged with orange ; a tree seldom more than 4 decimeters in diameter near the base. 21. Quercus catesbxi (p. 42). Pores in early wood elliptical or oval; wood light brown and faintly tinged with red; a tree often G to 8 decimeters in diameter near the base. 22. Quercus digitata (p. 43). Pores in early wood arranged chiefly in 3 to 5 rows.' Wood-parenchyma fibers in late wood arranged in conspicuous, tangential bands more than one cell wide. Pores in early wood very numerous and from 0.2 to 0.4 millimeter in diameter. Pores filled with tylo.ses 23. Quercus marilandica (p. 44). Pores with very little tyloses 24. (Quercus coccinea (p. 45). Pores in early wood less numerous and from 0.15 to 0.25 millimeter in diameter. Pores in late wood 0.05 millimeter in diameter. 25. Quercus brevifolia (p. 46). Pores in late wood 0.025 millimeter in diameter. 26. Quercus palustris (p. 46). 24 IDENTIFICATION OF NORTH AMERICAN OAK WOODS. Wood-parenchyma fibers in late wood scattered irregularly among the wood fibers, or sometimes arranged in much interrupted, inconspicuous, tan- gential bands one cell wide. Wood-parenchyma fibers very abundant in early wood; crystals of calcium oxalate numerous in pith ray cells 27. Quercus tcxana (p. 48). Wood-parenchyma fibers arranged in two or more double, concentric bands around the pores in early wood; crystals of calcium oxalate in pith ray cells very rare 28. Quercus velutina (p. 48j. Wood-parenchyma fibers grouped irregularly around pores in early wood; crystals of calcium oxalate very rare 29. Quercus rubra (p. 49). B. Little distinction between early and late wood. EVERGREEN OAKS, EXCEPT NO. 33. 1. Pores chiefly arranged in distinct radial rows. Radial rows of pores in late wood usually single. Tangential bands of wood-parenchyma fibers distinct. 30. Quercus arjrifoHa (p. 51). Tangential bands of wood-parenchyma fibers rather indistinct. 31. Quercus wislizeni (p. 51). Radial rows of pores in late wood usually double. Tangential bands of wood-parenchyma fibers very short and confined to the outer portion of the late wood; in early wood these elements scattered. 32. Quercus chrysolepis (p. 53). 2. Pores rather uniformly distril)uted throughout the annual layers of growth. Pores in early wood twice the size of those in late wood ; annual rings of growth very narrow; heartwood dark or nearly black. . .33. Quercus douglasii (p. 53). Pores in early and late wood nearly imiform in size; annual rings of growth wider; wood very light brown 34. Quercus densiflora (p. 54). Pores few, only slightly diminishing, but uniformly distributed across the annual rings of growth 35. Quercus virghiiana (p. 55). CHARACTERISTICS OF THE DIFFERENT OAK WOODS. 1. Laurel Oak (Quercus laurifolia Michaux) . (Fig. 11.) Heartwood dark brown tinged with red; sap wood thick and some- what ligliter colored. Wood hard, heavy, strong, rather coarse- grained, and not very dm'able in contact with the soil. Rate of growth rather slow, requiring on an average from 10 to 12 years for the tree to increase 1 inch in diameter. Vessels (lig. 11, v.) in early wood (e. u\) 1 or rarely 2 rows deep, round and approximately 0.25 ^ millimeter in diameter, diminishing abruptly in late wood (/. w.) to about 0.12 millimeter. Small vessels in radial row^s extending to the periphery of the annual ring of growth. Wood Jibers (w. f.) very numerous both in the early and late wood, averaging 1.34 millimeters long and approximately 0.021 millimeter wide. Cell walls thick and the cavities rather small. Wood-parenchyma Jibers uniformly distributed throughout the entire annual ring of growth. In the late wood they are arranged in single, irregular, indistinct tangential l)ands. Pith rays: Large pith rays 1 See footnote 1, p. 15. CHARACTERISTICS. 25 (Z. p. r.) from 25 to 40 cells wide and from three to four times as high and from 2 to 3 millimeters apart; small pith rays {s. p. r.) rarely more than 1 cell wide and from a few to 15 cells liigh. The wood of laurel oak resembles that of live oak {Q. virginiana), but is easily distinguished by its less prominent pith rays and more distinct annual rings of growth. 2. Gambel Oak (Quercus gambelii Nuttall). (Fig. 12.) Heart wood dark brown tinged with red; sap wood rather tliin and m.uch lighter colored. Wood hard, heavy, strong, close-grained. Fig. 11. Fig. 12. Fig. 11.— Laurel oakiQuercus laurifoHa). Transverse section through two entire annual rings of growtli; a. T., annual nng; e. w., early wood; /. ic, late wood; Z. p. r., largo pith ray; 5. p. r., small pith ray; v., vessel; iv.f., wood fiber; w.p./., wood-parenchyma fiber. Magnified 20 diameters. Fig. 12. — Gambel oak {Quercus gambelii). Transverse section through six entire annual rings of growth: e.w., early wood; l.w., late wood; Lp. r., large pith ray; s. p. r., small pith ray; v., vessel; w./.,wood fiber; w. p.f., wood-parenchyma fiber. Magnified 20 diameters. and fairly durable in contact with the soil. Rate of growth exceed- ingly slow, requiring on an average from 15 to 20 years to grow 1 inch in diameter. Vessels (fig. 12, v.) seldom more than 2 rows deep, round or occa- sionally in wide annual rings of growth elliptical or oval, and approxi- mately from 0.1 to 0.25 millimeter in diameter. Vessel walls in early wood thicker than those in late wood. Small vessels in late wood abruptly smaller, seldom over 0.025 millimeter, forming from 1 to 3 single, or rarely double, irregular, radial rows extending across the entire width of the annual ring of growth. Woodjihers (w. f.) nu- merous in early wood, averaging 1.16 millimeters long and 0.018 milli- 7718°— Bull. 102—11 4 26 IDENTIFICATION OF NORTH AMERICAN OAK WOODS. meter wide. Walls exceedingly thick and cavities small. Wood- 'parenchy ma fibers (w. p. f.) cliiefly surround large and small vessels. In outer portion of late wood these cells are arranged in tangential bands from 2 to 4 cells wide and near the early wood only 1 cell wide. Crystals of calcium oxalate very numerous. Pith rays: Large pith rays (I. p. r.) very conspicuous, from 35 to 45 cells wide and from three to five times as liigh and from 1.5 to 2.5 millimeters apart. Individual cells generalh^ filled ^vdth dark-brown coloring matter consisting of starch, tannin, and crystals of calcium oxalate. The small pith rays (s. p. r.) only 1 cell wide and from 4 to 15 cells liigh. The wood of gambel oak can be distinguished from that of the garry oak {Q. garryana), with wliich it may be confused, by its dark- brown color. 3. Pacific Post Oak {Quercus garryana DouglsiB) . (Fig. 13.) Heartwood light yellow and clearly distinguished from the tliin and nearly white sapwood. Wood is hard, exceedingly tough, close- grained, and very durable. Rate of growth rather slow, requiring from 12 to 15 years to increase 1 inch in diameter. Vessels (fig. 13, v.) in early wood 2 or rarely 3 rows deep, oval, with an average radial diameter of 0.35 millimeter and tangential diameter of 0.25 millimeter. In late wood (I. w.) they abruptly diminish to a uniform size of about 0.05 millimeter in diameter, arranged in two wide radial rows surrounded by numerous concen- tric bands of wood-parenchyma fibers visible under the compound microscope. Walls of small vessels in late wood tliinner than those in earl}' wood. Wood fibers {w. f.) on an average 1.3 millimeters long and about 0.018 millimeter wide. Walls thick and cavities small, occurring in more or less isolated and compact groups between the radial rows of small vessels and tangential bands of wood-paren- chyma fibers. Wood- pare ncliy ma jihers {w. p. f.) very abundant in early wood; also forming concentric bands around the small vessels in the radial rows and from 3 to 5 narrow, conspicuous tangential bands in late wood. Pith i^ays: Large pith rays (Z. p. r.) are about 300 cells wide and from four to five times as high and from 3 to 4 millimeters apart. Small pith rays {s. p. r.) are onl}" a single eel wide and. from a few to 20 cells high. (See reference under Valley oak to possible confusion of this wood with others.) 4. Valley Oak (Quercus lobata Nees von Esenbeck). (Fig. 14.) Heartwood light brown tinged with jxhI; sapwood rather thin and much lighter colored. Wood hard, heavy, rather fine-grained, brittle, and durable in contact with the soil. Although individual trees of this species grow moderately fast, most samples show that from 12 to 18 years are required for, a tree to grow 1 inch in diameter. CHARACTERISTICS. 27 Vessels (fig. 14, v.) in early wood {e. w.) 1 to 2 rows deep, round, varying from 0.2 to 0.5 millimeter in diameter, and generally filled with tyloses (t.); in late wood (I. w.) they become abruptly smaller, averaging approximately 0.06 millimeter and are distributed uni- formly across the late wood. Wood f hers (w. f.) average about 1.24 millimeters in length and are chiefly confined to late wood; early wood being almost wholly composed of large vessels and wood- parenchyma fibers. Cell walls thick with rather small cavities. Wood-parenchyma fihers (w. p. f.) abundant in early wood, surround- FiG. 13. Fig. 14. Fig. 13. — Pacific post oak ( Quercus garryana). Transverse section tlirougli one entire annual ring of growth ; e. w., early wood; I. w., late wood; I. p. r., large pith ray; s. p. r., small pith ray; v., vessel; w.f., wood fiber; w. p.f., wood-parenchyma filler. Magnified 20 diameters. Fig. 14. — Valley oak {Quercus lobata). Transverse section through three entire annual rings of growth; e.w., early wood; Z.w.,late wood; I. p. r., large pith ray; s. p. r., small pith ray; t'., vessel; v.f., wood fiber; w. p.f., wood-parenchyma fiber; t., tyloses. Magnified 20 diameters. ing large pores; more sparingly found in late wood with an almost entire absence of tangential arrangement. Numerous calcium oxalate ciystals present. Pith rays: Large pith rays (Z. p. r.) are from 10 to 25 cells wide, and from two to six times as high and from 1 to 4 millimeters apart. Small pith rays (s. p. r.) inconspicuous and very irregular on account of the numerous pores which they avoid. The v/ood of valley oak is distinguished from blue oak (Q. dougJasii) by its lighter brown color, and from the similar garry oak (Q. gar- ryajia) by the latter's very much wider pith raj's. 28 IDENTIFICATION OF NORTH AMERICAN OAK WOODS. 5. Netleaf Oak (Quercus reticulata Humboldt, Bonpland and Kimth). (Fig. 15.) Heartwood dark brown and occasionally tinged with red; sapwood thick and much lighter colored. Wood hard, heavy, very close- grained and not very durable in contact with the soil. Very little contrast between early and late wood. Rate of growth very slow, requiring from 12 to 18 years to grow 1 inch in diameter. Vessels (fig. 15, v.) in early wood (e. w.) from 1 to 3 interrupted rows deep, varying in diameter from 0.05 to 0.2 millimeter; those L^^Hl >, Fig. 15. Fig. 16. Fig. 15. — Netleaf oak {Quercus reticulata).— Transverse section through two entu-e annual rings of growth; e.w., early wood; Z. w.Jatew^ood; Z. p. r., large pith ray; s. p. r., small pith ray; v., vessel; M'./., wood fiber; w. p.f., wood-parenchyma fiber. Magnified 20 diameters. Fig. 16. — Arizona white oali (Quercus arizonica). Transverse section through one annual ring of growth e.M., early wood; Z.w., late wood; Z. p. r., large pith ray; s. p. r., small pith ray; «;., vessel; w./., wood fiber; w. p.f. , wood-parenchyma fiber. Magnified 20 diameters. first formed often much smaller than many in the late wood (I. w.), which are arranged in single or double and irregular radial rows, and surrounded by numerous wood-parenchyma fibers. Wood fibers (w. /.) average 1.06 millimeters long, with very thick walls and small cavities; onl}^ sparingly found in early wood. Wood-paren- cJiyma fibers (w. p. /.) A^ery abundant in late wood, occurring in numerous broad tangential bands from 0.2 to 0.5 cell wide and extending from ray to ray as uninterrupted lines. Crystals of calcium oxalate very numerous. Pith rays: Large pith ra^^s (Z. p. r.) very numerous and from 20 to 40 cells wide and from three to five times as high. Crystals of calcium oxalate present. Small pith CHARACTERISTICS. 29 rays (s. p. r.) only a single cell wide and from 4 to 20 cells high, rather inconspicuous 6. Arizona White Oak {Quercus «n2ow>a Sargent) . (Fig. 16.) Heartwood dark brown or sometimes nearly black; sapwood thick and much lighter colored. Wood hard, very heavy, strong, close- grained, very durable in contact with the soil, and exceedingly variable in its general gross characters. Rate of growth rather slow, requiring from 15 to 18 years for the tree to grow 1 inch in diameter. Vessels (fig. 16, v.) in early wood {e. w.) 1 to 2 rows deep, round and from 0.2 to 0.3 millimeter in diameter, becoming abruptly smaller in late wood {I. w.), where they are from one-fourth to one-third as large as those in early wootl and of nearly uniform diameter. Walls of small vessels in late wood thicker than those of larger pores in early wood. Distribution of small pores rather irregular, though a slight resemblance to radial arrangement present in wood showing wide annual rings of growth. Wood-Jibers (w. /.) form bulk of late wood, but are seldom present between larger pores in early wood. Walls rather thick and cavities small. Lengtli varies from 0.71 to 1.42 millimeters with average width of O.OIS millimeter. Wood-parenchyma fibers {v:. p. f.) almost entirely con- fined to early wood, forming the bulk of the elements which compose the inner half of annual rings of growth. Almost entire absence of tangential arrangement in late wood; traces of such bands present in outer portion. Pith rays: Large pith rays (Z. p. r.) very numer- ous, from 20 to 30 cells wide, from three to four times as high and from 1.5 to 3.5 millimeters apart; the cells contain numerous crystals of calcium oxalate. Small pith rays {s. p. r.) inconspicuous, only a single cell wide and from 3 to 15 cells high. 7. Post Oak {Quercus minor (Marsh) Sargent). (Fig. 17.) Heartwood light brown or sometimes tinged with red; sapwood thick and lighter colored. Wood very heavy, hard, close-grained, and in durability compares with that of white oak. Rate of growth rather slow, requiring approximately 16 years to grow 1 inch in diameter. Vessels (fig. 17, v.) in early wood {e. w.) generally 2 rows deep, round, and about 0.2 millimeter in diameter. In late wood (I. w.) nearh' uniform in size, approximately one-third as large as those in early wood and arranged in nearly regular radial rows of from 3 to 5 between the large pith rays. Wood fihers (w. f.) compose major part of annual rings of growth. W^alls very thick, rendering the wood exceedingly hard and heavy. Length varies from 0.83 to 1.25 millimeters with an average of 0.98 millimeter. Wood-parenchyma fibers {w. p. f.) occur sparingly in early wood. From 4 to 10 incon- spicuous tangential bands of average width in late wood. Pith rays: Large pith rays (I. p. r.) are about 25 cells wide and about four times 30 IDENTIFICATION OF NORTH AMEEICAN OAK WOODS. as high and 3 minimeters apart. Approximately 30 small rays (s. p. r.) only a single cell wide occur between the large rays. Post oak resembles white oak (Q. alba), but is distinguished from it by more numerous and conspicuous pith rays and smaller pores in the early wood. 8. Swamp White Oak (Quercus platanoides (Lambert) Sud worth). (Figs. 18 and 19.) Heartwood light brown, sometimes slightly tinged with red; sap- wood ratlier thin and somewhat lighter colored. Wood very hard, heavy, strong and equally as du- rable in contact with the soil as white oak. R ate of growth moder- ately fast, requiring on an average about 9 years to grow 1 inch in diameter. Vessels (fig. 19, v.) in early wood {e. w.) from 1 to 3 rows deep ; the inner row usually large and ellipti- cal, and the succeeding rows usu- ally very much smaller and round. Large vessels from 0.2 to 0.3 milli- meter in diameter. In late wood (Z. w.) they become abruptly smaller and arranged in moi-e or less narrow, radial rows, of which there are frequently from ten to twelve between the large pith rays (1. p. r.). Occasionally these ra- dial rows originate in the middle of late wood and extend to the outer part of annual ring of growth. They average about 0.04 millimeter in diameter. Wood fibers (w. f.) approximately 1.04 millimeters long with tluck walls and relatively small cavities. Wood-parenchyma fibers {w. 'p. f.) chiefl}" confined to the early wood, but border small vessels in late wood. They are arranged in numerous, inconspicuous, tangential bands in late wood. Pith rays: Large pith rays {I. p. r.) are from 15 to 25 cells wide, from three to four times as high, and from 8 to 10 millimeters apart. Small rays {s. p. r.) exceedingly numerous but seldom more than 1 cell wide. Swamp white oak superficially resembles white oak {Q. alba), from which it is distinguished by its very light-brown color, contrasting more or less shar])ly with the reddish-brown color of white oak wood. Fig. 17. — -Post oak {Quercus minor). Transverse section through one entire annual ring of growth; €. w., early wood; I. u\, late wood; I. p. r., large pith ray; s. p. r., small pith ray; v., vessel; «'./., wood fiber. Magnified 20 diameters. CHARACTERISTICS. 31 9. Emory Oak (Quercus emoryi Torrey), (Fig. 20.) Heartwood dark brown or sometimes nearly black; sapwood rather thick and light brown, tinged with red. Wood hard, heav^', strong, close-grained, and not durable m contact with the soil. Wood of old or slow-growmg trees very brittle. Rate of growth very slow, requiring from 12 to 15 years to grow 1 inch in diameter. Vessels (fig. 20, v.) in early wood (e. w.) are from 2 to 4 rows deep and vary from 0.15 to 0.35 millimeter in diameter, gradually diminish- ».Swf>i*T^Jlfefi- Fig. 18. Fig. !■ Fig. is.— Swamp white oak (Qmctcws platanoidcs) . Transverse section through 13 entire annual rings of growth. Magnified 20 diameters. Fig. 19.— Swamp white oak (Quercus platanoides). Transverse section through one entire ring of annual growth; e. «'., early wood; 1. w., late wood; I. p. r., large pith ray; «. p. r., small pith ray; v., vessel; w.f., wood fiber; u\ p.f., wood-parenchyma fiber. Magnified 20 diameters. ing in size in late wood Q,. w.), where they are 0.1 millimeter or less in .diameter. Small vessels arranged in regular single or rarely double radial rows extending to the outer part of the annual ring of growth. Usually two, though occasionally 1 and rarely 3 or 4 radial rows of small vessels between the large pith ravs. Walls of small A^essels thicker than those of large ones in early wood. Wood fibers iw. f.) on an average 1.12 millimeters long and about 0.02 millimeter wide. Walls tliick and the cavities very small, especially near the periphery of the amiual rings of growth. Wood- parenchyma fibers (w. p. /.) very abundant in earh^ wood and along the radial rows of small ])ores. Numerous single or double tangential bands in late wood. Pith rays: Large pith rays (I. p. r.) arc very numerous and vary from 10 to 25 32 IDENTIFICATION OF NORTH AMERICAN OAK WOODS. cells wide, from three to four times as high, and from 1.5 to 2.5 milli- meters apart; conspicuous in transverse sections. Small pith rays (s. p. r.) conspicuous and cells unusuall}" large compared to those of otlier oaks. Crystals of calcium oxalate usually confined to cells of large pith rays and to wood-parenchyma fibers. 10. California Black Oak (Quercus calif ornica (Torrey) Cooper). (Fig. 21.) Heartwood bright red or tinged with yellow; sapwood thin, lighter colored and easily distinguished from lioartwood. Wood hard, Fig. -20, Fig. 20. — Emory oak {Quercus emoryi). Transverse section through parts of two annual rings of growth; e. w., early wood; I. w'., late wood; I. p. r., large pith ray; s. p. r., small pith ray; v., vessel; w.f., wood fiber; j^;. p./., wood-parenchyma fiber. Magnified 20 diameters. Fig. 21.— California black oak (Quercus californica). Transverse section through one entire annual ring of growth; e. w., early wood; I. w., late wood; I. p. r., large pith ray; s. p. r., small pitli ray; v., vessel; w.f., wood fiber; iv. p.f., wood-parenchyma fiber. Magnified 20 diameters. heavy, strong, though brittle, rather close-grained and not durable in contact with the soil. The tree requires from 12 to 15 years to grow 1 inch in diameter. Vessels (fig. 21, v.) in early wood {e. w.) from 3 to 5 rows in mod- erately fast-growing trees, occupying about one-fifth of the width of the annual ring of growth; the vessels are from 0.2 to 0.45 millimeter in diameter. Small vessels in late wood (J. w.) occur in single or double and rather irregular radial rows extending to the outer edge of the annual ring, usually uniform in size and measuring about 0.1 millimeter in diameter. Wood fibers {w.f.) form the bulk of late wood CHARACTERISTICS. 33 / / and are approxiinatcl}- 1.21 niillimeters long and about 0.022 milli- meter wide. Wood- parenchyma fibers (w. p. /.) conspicuously ar- ranged in irregular ,tan^0ntial bands from 2 to 6 cells wide. In early wood they are lilled either with starch, tannin, or crystals of calcium oxalate. Pith rays: Large pith rays (I. p. r.) from 10 to 30 cells wide, from three to five times as high, and from 2 to 3 millimeters apart. Small ]uth rays (s. p. r.) very clearly defined in transverse sections. 11. White Oak {Quercus Gi6a Linnaeus). (Fig. 22.) Heartwood reddish brown; sapwood narrow and light colored. Wood very hard, heavy, strong, close-grained, and very durable in contact with the soil. Rate of growth moderately fast, requir- ing about 10 years to grow 1 inch in diameter. Vessels (fig. 22, v.) in early wood {e. w.) round, from 0.3 to 0.5 millimeter in diameter, and 1 row, or rarely 2 or more rows, deep. In late wood (I. w.) ves- sels abruptly diminish in diame- ter to approximately one-sixth of that in early wood, where they vary but little in size and out- line. Practically all the large vessels are filled with tyloses (t. ) . Wood fibers (w. /.) from 1 to 1.63 millimeters long and about O.OIS millimeter in diameter, forming the bulk of late wood. They have very thick walls and consequently rather small cavi- ties. Wood -parenchyma fibers {w. p. f.) scattered irregularly throughout the early wood. In late w^ood they occur in distinct single or double irregular, tangential bands, varying from a few to many, depending upon the width of the annual rings of growth. Pith rays: Large pith rays (I. p. r.) are from 10 to 40 cells w^ide, and from three to five times as high, and approximately 0.4 millimeter apart. Small pith rays (s. p. r.) usually 1 cell wide, though some rays are from 2 to 3 cells wide and from a few to 20 cells high. The wood of white oak is readily distinguished from that of red oak by the fact that the pores in the late wood diminish abruptly in Vft Fig. 22.— White oak {Quercus alba). Transverse sec- tion through one entire annual ring of growth; e. w., early wood; I. w., late wood; I. p. r., large pith ray; s. p. T., small pith ray; v. vessel; w. /., wood fiber; w. p.f., wood-parenchyma fiber; t., tyloses. Magni- fied 20 diameters. 34 IDENTIFICATION OF NORTH AMERICAN OAK WOODS. tlie former, while in the hitter they diminish gradually in size. Another character helpful in separating these two species is the pres- ence of tyloses within the pores of white oak and their absence in those of the red oak. White oak wood may be confused with the wood of bur oak (Q. macrocarpa), swamp white oak (Q. platan oide s) , post oak (Q. minor), chestnut oak {Q. prinus), cow oak (Q. micJiauxii), chinquapin oak ar Fig. 23 Fig. 23.— Bur oak {Quercus macrocarpa). Transverse saction through three entire aiinaal rin,c;s of growth; a. r., annual ring. Magnified 20 diameters. Fig. 24.— Bur oak {Quercus macrocarpa). Transverse section through one entire annual ring of growth; e. w., early wood; /. «,'., late wood; /. p. r., large pith ray; s. p. r., small pith ray: v., vessel; r. r., radial row; w.f., wood fiber: ir. p.f., wood-parenchyma filipr: /., tyloses. Ma'ini.'ied 20 diameters. {(}. acnminata), and overer.p oak (Q. lyrata). See special distinctions under each. 12. Bur Oak (Quercus macrocarpa Micliaux). (Figs. 23 and 24.) Ileartwood dark, rich brown in color; sapwood thin and much lighter in color. Wood hard, heavy, very strong and tough, close- grained, and not liable to warp or check. Lumber never distin- guished from white oak (Quercus cdha) on the market. The most valuable timber of the American oaks. This oak has the power to adapt itself to great variation of soil and climatic conditions, which enables it to live from Maine to Manitoba and southwest to Texas. The character of the wood pro- duced under favorable conditions varies considerably from tliat pro- duced near the limits of its botanical distribution. Illustrations of CHARACTERISTICS. 35 transverse sections of different samples of wood are here shown. Figure 24 shows a transverse section of wood collected in southern Indiana, where tlie bur oak attains its largest size and greatest value; the wood from which figure 23 was made was collected in north- western Minnesota, where this species approaches the chaparral form and consequently has very narrow annual rings of growth (fig. 23, a. r.). Bur oak may often be distinguish-ed from white oak by its wider radial rows of small vessels (fig. 24, r. r.) in late wood (J. w.). In white oak small pores often form a single narrow and rather regular row between the large pith rays (/. p. r.); while in the bur oak they are scattered in several rather wide bands bordered by wood-paren- chyma fibers {v\ p. f.), which often renders the wood somewhat lighter than that of white oak. Tangential bands of wood-paren- chyma fibers are more conspicuous in bur oak. The wood fibers (w.f.) average about 1.35 millimeters long and 0.021 millimeter in diameter. Large pith rays (I. p. r.) are about 6 millimeters apart. 13. Durand Oak (Quercus hreviloha (Torrey) Sargent). (Fig. 25.) lleartwood small and brown in color; sa})wood thick and much lighter colored. Wood moderatel}" hard, rather light, though brittle, and in general appearance resembles white oak; not durable in contact with the soil. Rate of growth very slow, especially near its limits of distribution, requiring approximately 15 years to grow 1 inch in diameter. Vessels (fig. 25, v.) in early wood (e. id.) oval and generally only a single row deep; generally contain considerable tyloses {t.). Small vessels in late wood (Z. iv.) surrounded by wood-parenchyma fibers («\ p.f.); they diminish in size abruptly and form broad radial rows (/'. /'.) which widen or become branched as they approach the periphery of the annual ring of growth (a. r.). Wood fibers (w.f.) chiefly occur in groups scattered tlirough the late wood. They are 1.23 millimeters long, vv'hich is only slighth' shorter than those of white oak. Walls thick and cavities small. Wood-parenchyma Jihers highly developed and largely confined to late wood, rendering the wood among the liglitest of the eastern oaks. Pith rays: Large pith rays (1. p. r.) from 10 to 30 cells wide and from three to four times as high. Distance between the large rays varies exceedingly in different parts of the same specimens. They are more numerous in this species, however, than in wb.it e oak. Small pith rays (s. p. r.) numerous but incon- spicuous, only a single cell wide and from a fev,' to 20 or more cells high. 14. Willow O&k (Quercus pheUos 'Linnseus). (Fig, 26.) lleartwood reddish brown, sometimes tinged with yeUow; sapwood thin and much lighter colored, though sometimes slightly tinged 36 IDENTIFICATION OF NORTH AMEEICAX OAK WOODS. with red. Wood moderately hard, heavy, strong, rather cross- grained, and moderately durable in contact with soil. Rate of growth usually rather slow, requiring from 10 to 15 years to grow 1 inch in diameter. Vessels (fig. 26, v.) in early wood (e. w.) are elliptical or oval in outline, with an average radial diameter of from 0.25 to 0.4 milli- meter ami tangential diameter of from 0.2 to 0.3 millimeter. Usually Fig. 25. Fig. 2G. Fig. 25.— Durand oak (Quercus hrcviloha). Tranverse section through three entire annual rings of growth; a. r., annual ring; e. w., early wood; I. w., late wood; /. p. r., large pith raj-; s. p. r., small pith ray; v., vessel; r. r., radial row; «'./., wood fiber; w. p./., wood-parenchyma fiber; /., tyloses. Magnified 20 diameters. » Fig. 26. — Willow oak {Quercus pheUos). Transverse section through one entire annual ring of growth; e. w.. early wood; I. w., late wood; I. p. r., large pith ray; s. p. r., small pith ray; v., vessel; w.f., wood fiber; w. p.f., wood-parenchyma filDer; /., tyloses. Magnified 20 diameters. only a single row of vessels within an annual ring of slow growing trees and chiefly filled with tyloses {t.); in fast growing trees usually from 2 to 3 rows, abruptly diminishing in size in late wood {I. id.). Small vessels often laterally compressed and irregular in outline and arranged in 2 or 3 rather conspicuous radial rows between the large pith rays. Wood fibers (w.f.) 1.52 millimeters long and 0.021 milli- meter wide. They are seldom found to any great extent in early wood, but form the bulk of elements in late wood between the radial rows of small vessels and entirely surrounded by wood-parenchyma fibers. Wood-parenchyma fibers (w. p. f.) are confined chiefly to early wood and bordering the small vessels in late wood. The tangential bands of wood-parenchyma f.bers, so common in most CHARACTERISTICS. 37 oaks, occur veiy sparingly in the wood of this species. There are a few short bands or groups of these elements, but usually they can be distinguished only under the microscope. Pitli rays: Large pith rays (i. p. r.) from 10 to 30 cells wide, and from two to four times as high, and from 2 to 3 millimeters apart. Small rays (s. f. r.) are, as a rule, only a single cell wide, and from a few to 20 cells high. The wood of willow oak, frequently confused with that of shingle oak {Q. imbricaria) , is distinguished by having less porous early wood than the latter, while the pores in the early wood of willow oak are usually elliptical, those in the shingle oak being round. 15. Overcup Osik (Quercushjrata Walter). (Fig. 27.) Heartwood dark brown and easily distinguished from the thick lighter-colored sapwood. Wood moderately hard, rather heavy, strong, and very durable in contact with soil. In its general appear- ance, physical characteristics, and rate of growth it is similar to white oak. Vessels (fig. 27, v.) in early w^ood (e. w.), 2 to 3 rows deep; and, as well as the smaller pores in late wood (l. w.), are slightly compressed laterally. They are abruptly smaller in diameter in late wood, forming broad and often rather irregular, radial bands surrounded by conspicuous and thin-walled w^ood-parenchyma fibers (r. r.). lloofZ fihers (w. f.) are 1.32 millimeters long and 0.022 milHmeter in diam- eter, and less numerous than those of white oak; their walls are usually somewhat thinner. Wood-par encliyTna fibers (w. p. f.) arranged in clearly defined tangential bands in late wood. The number of these bands varies with the width of the annual rings of growth. Pith rays: Large pith rays (Z. p. r.) are from 15 to 40 milh- meters wide and from three to five times as high. Small rays (s. p. r.) are only a single cell wide and from a few to 20 or more cells high. Overcup oak wood, sometimes confused with white oak (Q. alba), is readily distinguished from the latter by its larger and more niuner- ous pores in the early wood. 16. Cow Oak (Quercus micha.uxii Nuttall). (Fig. 28.) Heartwood light brown or somewhat tinged with red; sapwood thin and somewhat darker colored. Wood hard, heavy% tough, close-grained and durable in contact with soil. Under favorable conditions cow oak requires from 8 to 10 years to grow 1 inch in diameter. In the form of lumber it is seldom distinguished from white oak. Vessels (fig. 28, v.) in early wood (e. w.) from 2 to 3 rows deep, and approximately 0.5 millimeter in radial and 0.4 millimeter in tangen- tial diameter. In late wood (?. w.) small vessels arranged in 3 to 5 radial rows, which gradually widen or become branched near the periphery of annual rings of growth. Wood Jibers (w. f.) are thick walled and on an average 1.54 millimeters long and 0.021 milHmeter 38 IDENTIFICATION OF NORTH AMERICAN OAK WOODS. wide. They form the bulk of the elemeuts in kite wood. Wood- parencliyma fibers {w. p.f-) are confined chiefly to early wood, but also surround the smaller vessels in late wood. Narrow, irregular, tan- gential bands of wood-parenchyma fibers occur in the outer part of late wood. Pith rays: Large pith rays (I. p. r.) are from 20 to 40 cells wide and from one to three times as high. Small rays (s. p. r.) are exceedingly numerous and are only one cell wide and from a few to 20 or more cells high. Cow oak wood, whicli resembles white o:i!: {Q. alba) more closc^ly than that of any other species, is lighter colored end generally has Fig. 27. Fig. 2S. Fig. 27.— Overcup oak {Quercus lyrala). Transverse section through one entire annual ring of growth; e. w., early wood; I. uk, lale wood; I. p. r., large pith ray; s. p. r.. small pith ray; v., vessel; r. r., radial row; !«./., wood fiber; w. p. f., wood-parenchyma fiber; f., tyloses. Magnified 20 diameters. Fig. 28.— Cow oak {Quercus mkhauxii) Transverse sectioa through a portion of two annual rings of growth; e. «,'., early wood; /. w., late wood; I. p. r., large pith ray; s. p. r., small pith ray; v., vessel; r. r., radial row; u\f., wood fiber; tv. p.f., wood-parenchyma fiber; /., tyloses. Magnified 20 diameters. less conspicuous tangential ])ands of wood-parenchyma fibers in the late wood than white oak. 17. Chestnut Oak (Quercus prinus Linnteus). (Fig. 29.) Heartwood yellowish or reddish brown and sharply defined from the lighter and slightly reddish, narrow sapwood. Wood hard, hea^s^^, strong, tougli, moderately close-grained and durable in contact with soil. Rate of growth is low, requirmg from 12 to 20 years for the tree to grow 1 inch in diameter. Vessels (fig. 29, v.) round or elliptical in early wood (e. w.) and from 3 to 5 rows deep. Small vessels in late wood (?. w.) often polygonal CHARACTERISTICS. 39 and sometimes so small that their diameters hardly exceed those of wood-parenchyma fibere. Radial rows (/'. r.) of small vessels are wavy or slightly branched, and surrounded by numerous wood- parenchyma fibers which form narrow tangential bands (lo. p. f.) in late wood. Wooffhers (^v.f.) compose the bulk of late wood and are about 1.31 millimeters long and 0.020 millimeter wide, with thick walls and rather small cavities. Wood-jiarenchyma fhers (w. p. f.) are scattered in isolated groups in early wood. In late wood they occur in regular or branched and uninterrupted tangential bands which can be readily seen with the unaided eye. Pith rays exceedhigly numerous and constitute about one-fifth of the cellular sub- stance of the wood. Large pith rays (/. p. r.) are often 20 to 30 cells wide and from three to six times as high. Small pith rays (s. p. r.) only one cell wide and from 4 to 15 cells high, appear- ing as long, well-defined lines in transverse sections. The wood of chestnut oak is sometimes mistaken for white oak (Q. alba), but it is distin- guished from the latter by its more prominent pith rays and the lack of a faint reddish tinge present in the wood of white oak. 18. Chinquapin Oak (Qiiercus- a c u m i nata (Mi c h a u x ) Houba). (Figs. 30 and 31.) Heartwood light brown or slightly tinged with red; sa])- wood thin and lighter colored. Wood hard, heavy, strong, and close-grained. Its durability and chestnut oak. Vessels (fig. 30, v.) in early wood (e. w.) round or sometimes elUptical and from 0.15 to 0.35 millimeter in diameter; seldom formmg con- tinuous rows, but are generally arranged in groups of 2 to 5 vessels deep (fig. 31) between the large pith rays. Small pores in late wood (Z. w.) are about one-third as large as those of early wood, and with very thick walls compared w^ith those of the large pores which are usually filled with tyloses (fig. 30, t.). They are arranged in 3 to 5 ev/ Sp.T' Lp.T Fig. 29. — Chestnut oak {Qucrcus prinus). Transverse section through one entire annual ring of growth; f. w., early wood; I. «'.. late wood; I. p. r., large pith ray; s. p. r., small pith ray; v., vessel; r. r., radial row; u'.f., wood fiber; w. p. /., wood-parenchj-ma fiber. Magnified 20 diameters. rate of p;rowth similar to that of 40 IDENTIFICATION OF NORTH AMEEICAN OAK WOODS. rather irregular radial rows which extend to the periphery of the annual ring of growth where they are exceedingly small. Wood fibers (fig. 31, w. /.) composed mainly of thick-walled elements of about 1.15 millimeters in length. In very narrow annual rings of growth, such as are usually found near the periphery of the stem of old trees, the bulk of the wood substance consists of large vessels, wlule the remainder is mostly composed of thin-walled wood-paren- chyma fibers, which render the wood light and brittle. Wood- parenchyma f hers (fig. 31, w. p. f.) in early wood highly developed spr' Fig. ?a. Fig. 30. — Chinquapin oak {Quctcus acuminata). Transverse section through four entire annual rings of growth; e. w., early wood; I. w., late wood; I. p. r., large pith ray; s. p. r., small pith ray; r., vessel; t., tyloses. Magnified 20 diameters. Fig. 31. — Chinquapin oak (Quemis acuminata). Transverse section through one entire annual ring of growth; v., vessel; «''./., wood fiber; tc. p.f., wood-parenchyma fiber. Magnified 20 diameters. and scattered among the vessels. In late wood these fibers are found most abundantly near the small pores, and also in irregular and interrupted tangential bands. Pith rays: Large pith rays (fig. 30, Z. p. r.) from 10 to 35 cells wide, and from three to four times as high and about 3 millimeters apart. Numerous small pith ra3's (fig. 31, s. p. r.) only a single cell wide and from 3 to 15 cells high. Chinquapin oak is often sold as white oak {Q. alba) and is used for the same purposes, but it resembles chestnut oak {Q. jJnniis) more closely than it does white oak. It is distinguished from white oak b}' its dark-brown color, which contrasts more or less sharply with the reddish-brown tinge of the latter. The narrow amiual rmgs of CHARArTERTSTTC'ri. 41 growth and the proportionately larger amount of early wood than late wood of chmqiiapm oak will usually serve to separate it from chestnut oak. 19. Shingle Osi^ (Quercus imhricariaMivhiiux). (Fig. 32.) Heartwood light brown and slightly tinged with red; sapwood although somewhat lighter in color is not clearly distinguished from the heartwood. Wood hard, heavy, close-grained and rather tough. Rate of growth moderately fast, requiring from 10 to 12 years to grow 1 inch m diameter. Vessels (fig. 32, v.) in early wood {e. w.) occupy about one-half of the annual rings of growth. Large vessels from 3 to 6 rows deep and are more or less uniform in size and usually contain tyloses {t.). Their average radial diameter about 0.35 millimeter and tangential diameter about 0.25 millimeter, although in general outline the pores vary from round to elliptical or oval. In late wood (I. w.) t\\&j are of uniform size and only about one-eighth as large as those in early wood, and arranged in 2 or 3 single or double conspicuous radial rows. Wood fibers {w. /.) on an average 1.03 millimeters long and 0.017 millimeter wide and chiefly found between radial rows of small pores and wood-parenchyma fibers in late wood. Less than one-fifth of all the wood elements within annual rings of growth consist of wood fibers. Wood-parencJiyma fibers (w. p.f.) conspicuous in late wood, and form the bulk of elements surrounding the radial rows of small vessels. They branch out from these rows into tangential bands that can be readily seen with the unaided eye. There are from 8 to 1 2 of these bands to each annual ring of growth. Pith rays: I^arge pith rays (Jt. p. r.) from 15 to 40 cells wide and from two to four times as high. Small pith rays {s. p. r.) inconspicuous and, as a rule, only a single cell wide, and from 5 to 20 cells high. (See descri])tion under Willow oak {Q.. pheUos) for possible confusion with the wood of sliingle oak.) 20. Water Oak (Quercus nigra Linuiieus). (Fig. 33.) Heartwood light brown tinged with yellow; sapwood rather thick and lighter colored. Wood hard, rather close-grained and not durable in contact with soil. Rate of growth moderately fast, requiring from 10 to 12 years to grow 1 inch in diameter. Vessels (fig. 33, v.) in early wood (e. w.) arranged in from 1 to 3 tangential rows. Their tangential diameter varies from 0.14 to 0.28 millimeter and radial diameter from 0.16 to 0.35 millimeter. Vessels diminish gradually in size in late wood (J,, w.), where they are aiTanged in 2 or 3 single or double radial rows, extending to the periphery of the annual rings of growth. The average diameter of the small pores is about 0.05 millimeter. They are circular and have very tliick walls. V/ood ^bers (w. f.) vary in length from l.OS 42 IDENTTFICATION OF NORTPI AMERICAN OAK WOODS. to J.IK) millimeters, with an average length of 1.43 millimeters. Their walls are very thick and cavities small, forming the hard tissue between the radial rows of small vessels in late wood. The masses of hard fibers are intersected by very many small pith rays and by single or double tangential bands of wood-])arenchyma fibers. Wood-parencliyma Jihers (iv. p. /'.) very abundant both in early and late wood, and in the latter are arranged in numerous tangential bands, wliich are easily see^i with a pocket lens. There are from 5 to 15 of these bands in late wood, depending upon the ^'lp7 ^V^ Fi(,. .« SP^-- Fig. 32. Fig. .32.— Shingle oak {Quercus iinbricaria). Transverse section through one entire annnal ring of growth; f. w., early wood; 1. w., late wood; 1. p. r., largo pith ray; s. p. r., small pith ray: r.. vessel; w. /.. wood fiber; u\ p./., wood-parenchjTna fiber; t., tyloses. Magnified 20 diameters. Fig. .3.3.— Water oak (Qucrciis nigra). Transverse section through one entire annual ring of growth; r. u\, early wood; 7. ?/'., late wood; ?. p. r., large pith ray; s. p. r., small pith ray; v.. vessel; »•./., wood fiber; M'. p. /., wood-parenrhjTna flijer. Magnified 20 diameters. width of the annual rings of growth. Pith rays: Large pith rays (?. p. r.) from 15 to 40 cells wide, from tlu"ee to four times as liigh, and from 3 to 5 millimeters apart. The small pith rays (s. p. r.) are conspicuous, but only 1 cell wide and from 5 to 20 cells high. 21. Turkey O&k (Quercus cateshsei Michaux) . (Fig. 34.) Heart wood light brown tinged with red or yellow; sap wood tliick and somewhat lighter colored, though occasionally quite yellowish. Wood rather hard, heavy, medium close-grained and not very dura- ble in contact with the soil. Tliis species usually grows in dry uplands, where the rate of diameter increase is moderately slow, rcHpiiring from 10 to 15 years to grow 1 inch in diameter. CHAKACTERISTICS. 43 Vessels: Large vessels (fig. 34, v.) in early wood (r. lo.) from 1 to 3 rows deep, varying in diameter from 0.26 to 0.40 millimeter, but gradually diminishing in size toward the periphery of the annual ring of growth. Vessels in late wood (/. w.) vary from 0.10 to 0.20 millimeter in diameter and have very thick walls compared with those in early wood. There are from 1 to 3 irregular, interrupted radial rows of small pores between the large pith rays. Wood fibers (w. /.) tliick-walled and almost entirely confined to late wood, where they are scattered in small groups. Wooclfhers on an average Ipf Fig. 34. Ipr -' Fig. 3.5. Fig. 34. — Turkey oak (Quercus catesbxi). Transverse section through parts of two annual rings of growth; e. w., early wood; I. w., late wood; /. p. r., large pith ray; s. p. r., small pith ray; v., vessel. Magnified 20 diameters. Fig. 35.— Spanish oak (Quercus digitata). Transverse section through one entire annual ring of growth; e. te., early wood; I. w., late wood; I. p. r., large pith ray; s. p. r., small pith ray; v. vessel; w.f., wood fiber; w. p. /., wood-parenchyma fiber. Magnified 20 diameters. 1.47 millimeters long and about 0.026 millimeter wide. Wood- imrencliyma fibers abundant both in early and late wood, in the latter surrounding the smaller vessels and forming irregular, incon- spicuous, and much interrupted tangential bands. Usually from 6 to 10 of these bands within an annual layer of growth. Pith rays: Large pith rays (I. p. r.) from 20 to 45 cells wide, from two to four times as high, and from 2 to 4 millimeters apart. Cells in the small pith rays {s. p. r.) are large and the rays themselves quite conspicuous. 22. Spanish Oak {Quercus digitata (Marsh) Sudworth). (Fig. 35.) Heartwood reddish; sap wood thick and lighter colored, with a slightly brownish tinge. Heartwood resembles that of red oak, except that it is tinged brighter red. It is light in weight, though 44 IDENTIPTCATTON OF NORTH AMERICAN OAK WOODS. moclorately hard and strong, not durable in contact witli the soil, and moderately fast gi-owing, recjiiiring approximately 8 years to grow 1 inch in diameter. Vessels (fig. 35, v.) in early wood {e. w.) form a single interrupted row. They are elliptical or oval and vary from 0.15 to 0.25 milli- meter in diameter. Small pores on an average about 0.075 milli- meter in diameter, becoming smaller in late wood (/. iv.), where they form single radial and nearly parallel rows extending through the annual rings of growth. Wood Jihers (w.f.) very nmnerous in early wood, where they occur in small groups among the thinner-walled elements and gradually increase in number in late wood. In trans- verse section the}" are pentagonal in outline and have moderately tluck walls and small cavities. The individual fibers vary from 1.08 millimeters to 2 millimeters in length, with an average width of 0.024 millimeter. The wood of this species contains fibers having the greatest average length (1.65 millimeters). Wood-parendtyma Jibers {w. p. /.) arranged in concentric lines around the vessels in early wood and bordering the small pores in late wood. They also form irregular, narrow tangential bands in late wood. There are from 10 to 12 of these bands in annual rings of growth of moderately fast- growing trees. Pith rays: Large pith rays (I. p. r.) on an average about 20 cells wide and from two to three times as high, and from 2 to 4 millimeters apart. The height and width of the rays vary con- siderably, depending upon the age and size of the trees. Small pith ra3^s (s. p. r.) are numerous, and usually only 1 cell wide and from 8 to 16 cells high. The wood of Spanish oak is occasionally confused with red oak {Q. rubra), but is distinguished by having fewer and less-pronounced pith rays than red oak. 23. Blackjack Odik {Quercus 7na,rila,ndica^l\\eYic\\\\.). (Fig. 36.) Ileartwood dark brown; sap wood somewhat lighter colored and with a yellowish tinge. Wood hard, heavy, and not durable in con- tact with soil. Rate of growth comj^ares mtli that of post oak. Vessels (fig. 36, v.) in early wood (e. w.) usually 4 rows deejD and invariably filled with tyloses it.), round or seldom elliptical m outline and varying from 0.2 to 0.4 millimeter in diameter. Vessels in late wood (L ID.) about one-sixth as large as those in early wood, and arranged in irregular or branched radial rows. Small pores uniform in size with very thick walls. Wood fibers (w.f.) have veiy thick walls and rather small cavities. They vary from 1.04 to 1.63 milli- meters in length, with an average length of 1.38 millimeters, and are approximately 0.027 millimeter wide. Wood- parenchyma fibers {w. p. f.) are scattered in short, irregular, tangential bands or in small groujxs in late wood and surroimding the large and small vessels. CHAKACTESISTICS. 45 In radial section these elements may be seen with, the aid of a micro- scope in distinct parallel lines. Pith rays: Large pith rays (Z. p. r.) from 10 to 40 cells wide and from two to four times as high. Rays in the wood of trees grown in dry upland are more higldy developed than those in wood grown in rich moist lowlands. Small pith rays {s. J), r.) are exceedingly numerous and usually only one cell wide, occasionally 2 or 3, and from 10 to 20 cells high. 7! -tpr Fig. 3G. Fig. 37 Fig. 3G. — Blackjack {Qucrcus marilandica). Transverse section through one annual ring of growth; r. v., early wood; I. w., late wood; 1. p. r., large pith ray; s. p. r., small pith ray; r., vessel; w.f.. wood fiber; tv. p. /., wood-parench>^lla fiber. Magnified 20 diameters. Fig. 37. — Scarlet oak (Quercus coccinea). Transverse section tlirough two entire annual rings of growth; e. w., early wood; I. tc, late wood; I. p. r., large pith ray; s. p. r., small pith ray; t'., vessel; «'./., wood fiber; «'. p./., wood-parenchyma fil)er. Magnified 20 diameters. 24. Scarlet Oak (Quercus coccinea Muenchh.). (Fig. 37.) Heart wood reddish brown or slightly tinged with yellow; sap wood thick and much lighter colored. Wood hard, heavy, and tough and in its general properties and rate of growth compares with that of yellow oak. Approximately one-half of the annual ring of growth consists of early wood. Vessels (fig. 37, v.) in early wood (e. iv.) form a conspicuous ring from 3 to 5 rows deep. They are either round, elliptical, or oval and are from 0.2 to 0.4 millimeter in diameter; gradually diminishing in size in late wood (I. w.). In late wood they are arranged in smgle though more or less irregular radial rows, visible with a pocket lens or even wdth the unaided eye when perfectly smooth sections are 46 IDExXTIFICATIOK OF NORTH AMERICAN OAK WOODS. prepared. Walls of vessels in late wood are very thick, averaging 0.05 millimeter. There are from 2 to 4 conspicuous radial rows of small vessels between the large pith rays. Wood fibers (iv. f. ) are almost entirely wanting in early wood. They form a rectangular grouj) in late wood between the radial lines of small vessels and tan- gential bands of wood-parenchyma fibers. They have an average length of 1.49 millimeters and are approximately 0.023 millhneter wide. The longest individual fiber was found in the wood of this species, measuring 2.08 millimeters. Wood-parenchyma fibers (uk P-f-) are arranged principally in numerous tangential bands in late wood, where there are from 5 to 15 of such rows within an annual layer of growth of average width. Pith rays: Large pith rays (L p. r.) are about 30 cells wide and from three to four times as high. Small pith rays {s. p. r.) only a single cell wide and vary in height from several to 12 or 15 cells. Scarlet oak is often mistaken for yellow oak (Q. velutina), from which it can be recognized by its more or less reddish tinge, yellow oak having a yellowish tinge. Scarlet oak wood is sometimes con- fused also with red oak (Q. rubra), from which it is distinguished by its more pronounced reddish color and narrow annual rings of growth, red oak wood liavmg a pale red tinge and wide rings of growth. 25. Bluejack Oak (Quereus hrevifolia Sargent). (Fig. 38.) Ileartwood liglit brown and occasionally tinged with red; sapwood thick and dark brown and easily distinguished from the heartwood. Wood hard, strong, moderately close-grained, and not durable in contact with the soil. Vessels (fig. 38, v.) in early wood {e. w.) from 0.15 to 0.25 milli- metei' in diameter. They are from 3 to 5 rows deep and much interrupted, giving the ap])earance of a succession of gi'ou])s of vessels. Vessels diminish in size to less than 0.05 millimeter in diameter in late wood (L w.), forming from 3 to 5 irregular radial rows and having thicker walls than those in early wood. Wood fibers (w. f.) have an average length of 1.12 millimeters. They are not abundant ill early wood, but form the bulk of the elements between the radial rows of small vessels in late wood. Wood-parenchyma fibers (tv. p. f.) abundant both in early and late wood. They surround the large and small vessels, and in late wood occur in numerous, inconspicuous, irregular tangential bands. Pith rays: Large pith rays (L p. r.) are from 15 to 40 cells wide, from three to four times as high and 1 to 4 millimeters apart. Small pith rays {s. p. r.) are conspicuous in transverse sections, though seldom more than 1 cell wide and from 10 to 20 cells high. 26. Pin Oak {Quereus palustris Mlienchh.). (Fig. 39.) Heartwood dark brown tinged with red ; sapwood somewhat lighter, though occasionally slightly darker in color than the heartwood = CHARACTERISTICS. 47 Wood hard, heavy, tough, and coarse-gramed. Rate of growth and durabihty similar to that of willow oak. Vessels (fig. 39, v.) in early wood (e. w.) arranged in rather small groups between the large pith rays, and numbering from 6 to 12, nearly round pores, to each group; pores from 0.15 to 0.25 milli- meter in diameter. Small pores in late wood (J. w.) occur in rather irregular, interrupted radial rows, which originate near the middle of the late wood and extend to the periphery of the annual ring of growth. There are usually 3, but occasionally from 5 to 7, radial Fig. 39. Fig. 38.— Bliiejack oak (Quercus hredfoUa). Transverse section through one entire aiiuual ring of growth; f. ii'., early wood; ?.»■., late wood; /. p. r., large pith ray; s. p. r., small pith ray; v., vessel; w./., wood fiber; tv. y.f., wood-parenchyma fiber. Magnified 20 diameters. Fig. 39. — Pin oak {Quercus palustris). Transverse section through one entire annual ring of growth; e. w., early wood; I. w., late wood; I. p. r., large pith ray; s. p. r., small pith ray; v., vessel; «'./., wood fiber; w. p.f., wood-parenchyma fiber. Magnified 20 diameters. rows of small pores between the large pith rays. Wood fibers {w. f.) in early wood very sparse, but they form the bulk of the late wood. They are about 1.35 millimeters long and 0.017 millimeter wide. The cell walls are usually quite thin. Wood-parenchyma fibers (w. p.f.) abundant both in early and late wood. In the latter they are arranged in numerous distinct narrow bands, depending upon the width of the annual rings of growth. Pith rays: Large pith rays (Z. p. r.) are from 0.25 to 0.5 millimeter wide, from 7 to 15 millimeters high, and from 2 to 3 millimeters apart. Small pith rays (.., vessel; «•./., wood fiber; ic. p.f., wood-parenchyma fiber. Magnified 20 diameters. Fig. 43.— California live oak (Quercus agrifolia). Transverse section through two annual rings of growth; a. ?■., annual ring; Z. p. r., large pith ray; s. p. r., small pith ray; y., vessel; w./., wood fiber; w.p.f., wood-parenchyma filler. Magnified 20 diameters. walls and form from 3 to 6 radial rows extending across the width of the annual rings of growth. The size of the vessels gradually diminishes from the early to the late wood. Tliis is a constant character and may be rehed upon in separating the red oak from the white oak. In the latter the pores diminish abruptly. The average diameter of small vessels in late wood is about 0.08 milli- meter. Wood fibers (w. /.) compose the bulk of late wood. They have rather tliick walls and moderately large cavities. The average length of the fibers is 1.19 millimeters and the average width 0.018 millimeter. Wood-parenchyma fibers (w. p. f.) are scattered rather CHARACTERISTIC'S. 51 irregularly throughout the annual rings of growth and surround the large and small vessels. They also form narrow tangential bands in the late wood. Pith rays: Large pith rays (Z. i?. r.) are usually from 1 to 3 millimeters apart. Small pith rays (s. ]). r.) are very numerous and usually but 1 cell wide. The wood of this oak may be confused with Spanish oak (Q. digi- tata), scarlet oak (Q. coccinea), yellow oak (Q. velutina), pin oak (Q. palustris), and Texan oak (Q. texana). See description of ejich for special distinctions. 30. California Live Oak {Quercus agrifolia Nees von Esenbeck). (Fig. 43.) Heartwood light brown tinged with red; sapwood thick and slightly darker colored. Wood hard, heavy, close-grained, and rather brittle. Kate of growth exceedingly slow, requiring from 15 to 30 years to increase 1 inch in diameter. Vessels (fig. 43, v.) arranged in 2 or 3 radial rows between the large pith rays, showing very little contrast between early (e. w.) and late wood (I. w.). The absence of distinct tangential rows of pores renders it difficult to obtain figures on rate of growth. Ves- sels formed during the beginning of the growing season are usually larger than those formed later. Occasionally, however, the pores in the middle of the annual rings of growth are larger than near the inner boundary. Large vessels vary fi-om 0.15 to 0.25 milli- meter, while those near the periphery of the annual ring are only about one-half as large, and usually round, though sometimes slightly elongated radially. Wood fhers {w. f.) are, on an average, 1.34 millimeters long and have exceedingly thick walls and very small cavities. They are regularly arranged throughout the entire width of the annual ring. Wood-parenchyma fibers (w. p. f.) in early wood cliiefly surround vessels. Near the periphery of the annual ring of growth these elements are arranged in numerous irregular, tangential bands clearly distinguishable under the com- pound microscope. The wood of tliis species contains more wood- parenchyma fibers per unit area than that of any other oak. It also contains a great many crystals of calcium oxalate. Pith rays: Large pith rays (Z. p. r.) are from 15 to 30 cells wide, from three to four times as liigh, and from 3 to 6 milhmeters apart. Small pith rays (s. p. r.) are exceedingly numerous and are composed of unusually large cells. 31. Highland Live O&k {Quercus wislizeni K. deQsiwCioWe.) (Fig. 44.) Heartwood light reddish brown; sapwood thick and somewhat lighter colored. Wood hard, heavy, tough, moderately close-grained, and very durable in contact with soil. It is an evergreen oak with rather indistinct annual rings of growth, the boundaries of which 52 TDENTTFTCATION OF NORT?T AMERICAN OAK WOODS. can only be seen with the aid of a pocket lens magnifying 6 or 8 diam- eters. Rate of growth moderately slow, requiring from 12 to 15 years to grow 1 inch in diameter. Vessels (fig. 44, v.) in early wood (e. w.) from 1 or 2 interrupted tangential rows, gradually diminishing in size in late wood (/. iv.), where they are arranged radially in single or double rows across the annual rings of growth. The average width of vessels in late wood is about one-half of those in early wood. There are 2 or 3 distinct radial rows of small vessels between the large pith rays. Walls of Fig. 45, Fig. 44.— Highland oak (Quercus wislizeni). Transverse section through parts of two annual rings of growth; e. w., early wood; I. ?('., late wood; 7. p. r., large pith ray; s. p. r., small pith ray; v., vessel; w.f., wood fiber; w. p.f., wood-parenchyma fiber. Magnified 20 diameters. Fig. 45. — Canyon live oak (Quercus chrysolepis). Transverse section through three entire annual rings of growth; a. r., annual ring; I. p. r., large pith ray; s.p. r., small pith ray; v., vessel; w./., wood fiber; w. p./., wood-parenchyma fiber. Magnified 20 diameters. vessels very thick, especially in the outer part of late wood. Wood fibers {w.f.) about 1.16 milluneters long and 0.019 millimeter wide, with thick walls and exceedingly small cavities. Wood-2)arencJiyma fibers (w. y.f.) more or less evenly distributed throughout the annual layers of growth. Tangential bands not clearly visible with an ordinary pocket lens. Under the microscope they are shown to be irregular and greatly interrupted by wood fibers. Pith rays: Large pith rays (Z. p. r.) about 30 cells wide and from 2 to 3 millimeters apart. Small pith rays (s. p. r.) seldom more than a single cell wide and from 8 to 12 cells high. CHARACTEEISTICS. 53 32. Canyon Live Oak (Quercus chrysolepis Liebmann). (Fig. 45.) Heartwood light brown or sometimes tinged with red; sap wood (generally quite thick) is sometimes darker colored than the heart- wood. Wood very hard, heavy, strong, and not durable in contact with soil. In manner and rate of growth this species approaches the eastern live oak. Vessels: The manner in which the vessels (fig. 45, v.) in the annual rings of growth are grouped corresponds somewhat to that in the eastern live oak, except that in the former they are more numerous, particularly the smaller pores near the periphery of the annual ring of growth (a. r.). Vessels are usually round and vary from 0.08 to 0.2 millimeter in diameter. The walls of small pores are very thick and their cavities small. Wood Jihers {w. f.) uniforaily distributed throughout the annual rings of growth. They average 1.2 millimeters long and about 0.02 millimeter wide. The cell walls are veiy thick and the cavities small. Wood- parencJiyTna fibers {iv. p. f.) are scat- tered irregularly among the wood fibers. Near the periphery of the annual rings they are arranged in short tangential bands, seldom more than one cell in width. Pith rays: Large pith rays (l. jj. r.) are from 20 to 35 cells wide, from two to four times as high, and from 0.3 to 0.8 millimeter apart. 33. Blue Oak (Quercus douglasii Hooker and Arnott). (Fig. 46.) Heartwood dark bro^v^^ or sometmies nearly black when exposed; sap wood rather thick and of much lighter color. Wood moderately hard, heavy, coarse-grained, often very brittle, and not durable in contact with soil. Rate of growth slow, requiring from 15 to 20 years to grow 1 inch in diameter. Vessels (fig. 46, v.) vary from 0.05 to 0.25 millimeter in diameter. Individual vessels often extend across the entire width of the annual ring of growth (a. r.). These as well as the smaller vessels in late wood are surrounded by wood-parenchyma fibers, allowing compara- tively little space for the development of thick-walled wood fibers. Vessels have very thick walls, particularly the small ones in late wood. Wood fibers (w. f.) invariably found only near the periphery of wide annual rings of growth. They vaiy from 0.96 to 1.38 millimeters in length with an average length of 1.13 millimeters. Wood-parenchyma fibers (w. p.f.) scattered uniformly throughout, but are chiefly found bordering the vessels. They contain numerous crystals of calcium oxalate. Pith rays: Large pith rays (Z. p. r.) veiy numerous, from 15 to 35 cells wide, from two to four times as high, and from 1.5 to 3 millimeters ai)art. Small pith rays (s. p. r.) onXj a single cell wide and from 5 to 15 cells high; they are very irregular on account oi tlie small pores which they avoid. (For possible confusion of this wood with that of valley oak {Q. lobata) see description of the hitter.) 54 IDENTIFICATION OF KOKTII AMERICAN OAK WOODS. 34. Tanbark Oa,k (Quercusdensiflora Hooker emd Arnott). (Fig. 47.) lieartwood light brown or tinged with red; sap wood thick, dark brown or often tinged with yellow. Wood very hard, heavy, strong, and close-grained. Old and slow-growing trees produce wood that is very brittle and not durable in contact with soil. Rate of growth slow, recpiiring from 15 to 20 years for the average tree to grow 1 inch in diameter. Vessels (fig. 47, v.) arranged in rather wide radial rows which can be easilv seen on a smooth transverse section with the unaided eye. ar - L pr Vpf Fig. 40. Fig. ■!? Fig. 40.— (California) Rock oak (Quercus douglasii). Transverse section through IJ aimual rings of growth, o.r., annual ring; Z. p. r., large pith ray; s. p. r., small pith ray; ?)., vessel; )/'./.. wood fiber; ;<'. p./., wood- parenchyma filler. Magnified 20 diameters. Fig. 47.— (California) Tanbark oak (Quercus densiflora). Transverse section through one entire annual ring of growth; a. r., annual rmg; s. p. r., small pith ray; v., vessel; w.f., wood fiber; w. p.f., wood-paren- chyma fiber. Magnified 20 diameters. There is no sharp contrast between early and late wood. The boundaries of annual rings of growth (a. r.) are indistinctly marked by a few rows of radially compressed wood fibres. Although vessels are usually larger in early wood, they are sometimes larger in late wood and gradually increase in number toward the periphery where the radial rows are branched. The diameters of the pores vary from 0.05 to 0.3 millimeter with an average of about 0.15 milli- meter. Wood fibers (w. /.) average 1.23 millimeters long and are most abundant in earlv wood and near the middle of the annual CHAEACTEKISTICS. 55 rings. Wood-parenchyma fibers (w. jj. /.) very abundant between the large pores, forming conspicuous radial rows across the entire width of the annual rings of growth. They are also arranged in single or double conspicuous tangential bands. The late wood is largely composed of small pores and wood-parenchyma fibers. Pith rays: Large pith rays (I. p. r.) from 25 to 40 cells wide and from two to four times as high. Small pith rays (s. p. r.) are only a single cell wide and from 30 to 40 cells high. In a transverse section they are very conspicuous when viewed under the compound microscope. The cells composing the rays con- tain considerable starch, tannin, and numerous crystals of calcium oxalate. 35. live Oak (Quercus Virginia na Miller). (Fig. 48.) Heart wood light brown and tinged with yellow; sapwood'very thin and cream colored or some- times nearly white. Wood very hard, heavy, strong, and very durable in contact with soil. Rate of growth very slow, requiring on an average from 15 to 20 years to grow 1 inch in diamater. Vessels (fig. 48, v.) in early and late wood usually round and vary from 0.1 to 0.25 millimeter in di- ameter. Radial rows of small ves- sels so common in most American oaks are generally absent. Walls very thick, especially near the periphery of the annual rings of growth {a. r.). Wood fibers (w.f.) uniformly distributed and vary in length from 0.83 to 1.79 millimeters and about 1.39 millimeters in diameter. Walls very thick and the cavities small, thus giving to the wood its peculiar hardness and toughness which make it so valuable for construction purposes. The outer edge of each annual ring of growth is marked by 2 or 3 layers of wood fibers which are very much flat- tened radially. Wood-parencJiym a fibers (w. p. f.) occur in concen- tric bands around the larger vessels, but they are also arranged in irregular and inconspicuous tangential bands in late wood. The number of these bands varies with the width of the annual rings. Fig. 48. — Live oak (Quercus virginiana) . Trans- verse section through two entire annual rings of growth; a. r., annual ring; I. p. r., large pith ray; s. p. r., small pith ray; v., vessel; w.f., wood filler; uk p. /., wood-parenchyma fiber. Magnified 20 diameters. 56 IDENTIFICATION OF NORTH AMERICAN OAK WOODS. There are on an average about 10 such bands to each millimeter in radial distance. Pith rays: Large pith rays {I. p. r.) are from 25 to 50 cells wide, from two to four times as high, and from 1 to 3 milli- meters apart. The small pith rays (s. p, r.) are seldom more than 1 cell wide and from a few to 12 or 15 cells high. (For possible confusion of this wood with that of laurel oak {Q. laurifoUa) see description of the latter.) Table 1. — The lengths and widths of wood Jihers of the most important North American Species. Length. Width. Average. Maximum. Minimum. Average. Maximum. Minimum. (^uercus laurifolia Mm. 1.342 1.158 1..300 1.242 1.063 .921 .979 1.038 1.121 1.213 1.267 1.354 1.229 1. .521 1. 325 1.538 1.308 1. 154 1.0.33 1.433 1.471 1.646 1.375 1.488 1.121 1.354 1.367 1.300 1.188 1.358 1.163 1.204 1.133 1.225 1.388 Mm. 1.875 1.417 1. 625 1.542 1.333 1.417 1.250 1.250 1..500 1.458 1. 625 1.667 1.417 1.875 1.708 1.792 1.667 1.500 1.417 1.958 1.833 2.000 1.625 2.083 1.375 1.625 1.583 1.667 1.458 1.625 1.375 1.542 1.375 1.458 1.792 Mm. 0. 958 .875 1.083 .792 .750 .708 .833 .750 .833 .833 1.000 1.042 .875 1.167 1.000 1.083 .958 .917 .667 1.083 1.208 1.083 1.042 1.000 .792 1.042 1.167 .958 .708 1.042 .917 .917 .958 .958 .833 Mm. 0.021 .018 .018 .020 .017 .018 .014 .017 .020 .022 .018 .021 .018 .021 .022 .021 .020 .018 .017 .018 .026 .024 .022 .023 .018 .017 .023 .022 .018 .022 .019 .020 .018 .027 .016 Mm. 0.027 .019 .019 .023 .019 .019 .015 .019 .023 .027 .019 .023 .023 .027 .023 .023 .023 .023 .019 .023 .031 .027 .027 .031 .023 .019 .031 .027 .019 .031 .019 .023 .023 .031 .019 Mm. 0.019 gambelii .015 .015 lobata .015 reticulata .015 .015 minor . . .012 platanoides .012 .019 caUfomica .019 alba .015 .019 breviloba .015 phellos .015 lyrata .019 michauxii .019 prinus .019 .015 imbricaria. . . . .015 nigra .015 .023 digitata .019 marilandica .019 .019 brevifolia. . . . . .015 palustris .015 .015 velutina . .015 rubra .015 .015 wislizeni .019 .015 douglasii . . .015 densiflora .023 .015 o ^c '12