_b._ Three to six simple pits to each tracheid, on the walls of the cells of the pith ray.--Group 2. _P. taeda_, _palustris_, etc., including most of our "hard" and "yellow" pines. Section II. Walls of tracheids of pith ray smooth, without dentate projections. _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 clusters. _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 clusters 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 .....................................SASSAFRAS. 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 clusters 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.