296 WOOD AND FOREST. 



h. Resin duets 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 Speuce. 



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



brown; resin ducts very few, irregularly scattered (tracheids 



without spirals) Tamarack. 



II. — EixQ-PoRous Woods. 



(Some of Group D and cedar elm inipi-rfecl]^- rinfj-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. 



n..' Color of radial section not yellow x4sH. 



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

 hardness and weight, tliis species is easilj' recognized, 



OsAOE 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 bro\ra . .Black Locust. 



b. 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 tlie 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 traeheid on the radial walls of 

 the cells of the pith ray. — Group 1. Represented in this country only 

 by P. resinosa. 

 h. Three to six simple pits to each traeheid, on the walls of tlie cells of 

 the pith ray. — Group 2. /'. Inciln. iiiihislris. etc.. including most of our 

 "hard" and '\yellow" pines. 

 Section IT. \^;\lls of tracheids of pith ray smooth, without dentate projec- 

 tions. 



a. One or two large [lits to each traeheid on the radial walls of each cell 

 of the pith ray. — Group 3. P. strobiif:. lainbcitiinin, 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. parryaiia, and other nut pines, including also P. balfouriana. 



