Fig. 130. "Diffuse-porous" Woods. ar, annual ring; pr, pith rays which are "broad" at a, "fine" at b, "indistinct" at d.

Note.—The above described three groups are exogenous, i.e., they grow by adding annually wood on their circumference. A fourth group is formed by the endogenous woods, like yuccas and palms, which do not grow by such additions.

I.—Non-Porous Woods.

(Includes all coniferous woods.)
A. Resin ducts wanting.[1]
1. No distinct heart-wood.
a. Color effect yellowish white; summer wood darker yellowish (under microscope pith ray without tracheids)Firs.
b. Color effect reddish (roseate) (under microscope pith ray with tracheids)Hemlock.
2. Heart-wood present, color decidedly different in kind from sap-wood.
a. Heart-wood light orange red; sap-wood, pale lemon; wood, heavy and hard.Yew.
b. Heartwood purplish to brownish red; sap-wood yellowish white; wood soft to medium hard, light, usually with aromatic odor.Red Cedar.
c. Heart-wood maroon to terra cotta or deep brownish red; sap-wood light orange to dark amber, very soft and light, no odor; pith rays very distinct, specially pronounced on radial section.Redwood.
3. Heart-wood present, color only different in shade from sap-wood, dingy-yellowish brown.
a. Odorless and tasteless.Bald Cypress.
b. Wood with mild resinous odor, but tasteless.White Cedar.
c. Wood with strong resinous odor and peppery taste when freshly cut.Incense Cedar.
B. Resin ducts present.
1. No distinct heartwood; color white, resin ducts very small, not numerous.Spruce.
2. Distinct heart-wood present.
a. Resin ducts numerous, evenly scattered thru the ring.
a'. Transition from spring wood to summer wood gradual; annual ring distinguished by a fine line of dense summer-wood cells; color, white to yellowish red; wood soft and light.Soft Pines.[2]
b'. Transition from spring wood to summer wood more or less abrupt; broad bands of dark-colored summer wood; color from light to deep orange; wood medium hard and heavy.Hard Pines.[2]
b. Resin ducts not numerous nor evenly distributed.
a'. Color of heart-wood orange-reddish, sap-wood yellowish (same as hard pine); resin ducts frequently combined in groups of 8 to 30, forming lines on the cross-section (tracheids with spirals).Douglas Spruce.
b'. Color of heart-wood light russet brown; of sap-wood yellowish brown; resin ducts very few, irregularly scattered (tracheids without spirals).Tamarack.

[Footnote 1:] To discover the resin ducts a very smooth surface is necessary, since resin ducts are frequently seen only with difficulty, appearing on the cross-section as fine whiter or darker spots normally scattered singly, rarely in groups, usually in the summer wood of the annual ring. They are often much more easily seen on radial, and still more so on tangential sections, appearing there as fine lines or dots of open structure of different color or as indentations or pin scratches in a longitudinal direction.

[Footnote 2:] Soft and hard pines are arbitrary distinctions and the two not distinguishable at the limit.