296 WOOD AND FOREST. 



6. 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. 



&'. Color of heart-wood light russet brown; of sap-wood yellowish 

 brown; resin ducts very few, irregularly scattered (tracheids 

 without spirals) TAMARACK. 



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. 



&.' Color of radial section light yellow; by which, together with its 

 hardness and weight, this species is easily recognized, 



OSAGE ORANGE. 



6. 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. 

 &. Heavy; medium hard to hard. 



The following convenient and useful classification of pines into four groups, 

 proposed by Dr. H. Mayr, is based on the appearance of the pith ray as seen 

 in a radial section of the spring wood of any ring: 

 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. 



Section II. Walls of tracheids of pith ray smooth, without dentate projec- 

 tions. 

 a. One or two large pits to each tracheid on the radial walls of each cell 



of the pith ray. Group 3. P. strolus, lambertiana, and other true 



white pines. 

 6. 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 . 



