Chapter XIV: Section I: Walls of the tracheids of the pith ray with dentate

projections.

_a._ One to two large, simple pits to each tracheid on the radial
walls of the cells of the pith ray.--Group 1. Represented in
this country only by _P. resinosa_.

_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.