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_a._ One or two large pits to each tracheid on the radial walls of each cell of the pith ray.--Group 3. _P. strobus, lambertiana_, and other true white pines.
_b._ Three to six small pits on the radial walls of each cell of the pith ray. Group 4. _P. parryana_, and other nut pines, including also _P. balfouriana_.
II.--RING-POROUS WOODS.
(Some of Group D and cedar elm imperfectly ring-porous.)
A. Pores in the summer wood minute, scattered singly or in groups, or in short broken lines, the course of which is never radial.
1. Pith rays minute, scarcely distinct.
_a._ Wood heavy and hard; pores in the summer wood not in cl.u.s.ters.
_a.'_ Color of radial section not yellow.................ASH.
_b.'_ Color of radial section light yellow; by which, together with its hardness and weight, this species is easily recognized, ............OSAGE ORANGE.
_b._ Wood light and soft; pores in the summer wood in cl.u.s.ters of 10 to 30 .......................................CATALPA.
2. Pith rays very fine, yet distinct; pores in summer wood usually single or in short lines; color of heart-wood reddish brown; of sap-wood yellowish white; peculiar odor on fresh section .....................................Sa.s.sAFRAS.
3. Pith rays fine, but distinct.
_a._ Very heavy and hard; heart-wood yellowish brown.
BLACK LOCUST.
_b._ Heavy; medium hard to hard.
_a.'_ Pores in summer wood very minute, usually in small cl.u.s.ters of 3 to 8; heart-wood light orange brown.
RED MULBERRY.
_b.'_ Pores in summer wood small to minute, usually isolated; heart-wood cherry red ..........COFFEE TREE.
4. Pith rays fine but very conspicuous, even without magnifier.
Color of heart-wood red; of sap-wood pale lemon ...HONEY LOCUST.
B. Pores of summer wood minute or small, in concentric wavy and sometimes branching lines, appearing as finely-feathered hatchings on tangential section.
1. Pith rays fine, but very distinct; color greenish white.
Heart-wood absent or imperfectly developed ...........HACKBERRY.
2. Pith rays indistinct; color of heart-wood reddish brown; sap-wood grayish to reddish white .........................ELMS.
C. Pores of summer wood arranged in radial branching lines (when very crowded radial arrangement somewhat obscured).
1. Pith rays very minute, hardly visible .................CHESTNUT.
2. Pith rays very broad and conspicuous .......................OAK.
D. Pores of summer wood mostly but little smaller than those of the spring wood, isolated and scattered; very heavy and hard woods.
The pores of the spring wood sometimes form but an imperfect zone.
(Some diffuse-porous woods of groups A and B may seem to belong here.)
1. Fine concentric lines (not of pores) as distinct, or nearly so, as the very fine pith rays; outer summer wood with a tinge of red; heart-wood light reddish brown ....................HICKORY.
2. Fine concentric lines, much finer than the pith rays; no reddish tinge in summer wood; sap-wood white; heart-wood blackish .............................................PERSIMMON.
ADDITIONAL NOTES FOR DISTINCTIONS IN THE GROUP.
Sa.s.safras and mulberry may be confounded but for the greater weight and hardness and the absence of odor in the mulberry; the radial section of mulberry also shows the pith rays conspicuously.
Honey locust, coffee tree, and black locust are also very similar in appearance. The honey locust stands out by the conspicuousness of the pith rays, especially on radial sections, on account of their height, while the black locust is distinguished by the extremely great weight and hardness, together with its darker brown color.
[Ill.u.s.tration: Fig. 131. Wood of Coffee Tree.]
The ashes, elms, hickories, and oaks may, on casual observation, appear to resemble one another on account of the p.r.o.nounced zone of porous spring wood. (Figs. 129, 132, 135.) The sharply defined large pith rays of the oak exclude these at once; the wavy lines of pores in the summer wood, appearing as conspicuous finely-feathered hatchings on tangential section, distinguish the elms; while the ashes differ from the hickory by the very conspicuously defined zone of spring wood pores, which in hickory appear more or less interrupted. The reddish hue of the hickory and the more or less brown hue of the ash may also aid in ready recognition. The smooth, radial surface of split hickory will readily separate it from the rest.
[Ill.u.s.tration: Fig. 132. _A_, black ash; _B_, white ash; _C_, green ash.]
The different species of ash may be identified as follows (Fig. 132):
1. Pores in the summer wood more or less united into lines.
_a._ The lines short and broken, occurring mostly near the limit of the ring .......................................WHITE ASH.
_b._ The lines quite long and conspicuous in most parts of the summer wood .......................................GREEN ASH.
2. Pores in the summer wood not united into lines, or rarely so.
_a._ Heart-wood reddish brown and very firm ..............RED ASH.
_b._ Heart-wood grayish brown, and much more porous ....BLACK ASH.
In the oaks, two groups can be readily distinguished by the manner in which the pores are distributed in the summer wood. (Fig. 133.) In the white oaks the pores are very fine and numerous and crowded in the outer part of the summer wood, while in the black or red oaks the pores are larger, few in number, and mostly isolated. The live oaks, as far as structure is concerned, belong to the black oaks, but are much less porous, and are exceedingly heavy and hard.
[Ill.u.s.tration: Fig. 133. Wood of Red Oak. (For white oak see fig. 129, p. 291.)]
[Ill.u.s.tration: Fig. 134. Wood of Chestnut.]
[Ill.u.s.tration: Fig. 135. Wood of Hickory.]
