The Trees of Vermont 211 



hh. Rays (cross) not visible to the naked eye with 

 close scrutiny; pores (cross) not uniformly dis- 

 tributed, but somewhat larger and more numerous 

 in the spring wood; pith flecks (cross) usually 

 rather abundant ; wood light and soft. 

 i. Pores (cross) of spring wood visible to the naked 

 eye with close scrutiny; growth rings (cross) not 

 marked by narrow, whitish, concentric lines ; pith 

 flecks (cross) usually small, not conspicuous, 



Betula alba papyrifera. 

 ii. Pores (cross) of spring wood not visible to the 

 naked eye with close scrutiny ; growth rings 

 (cross) marked by narrow, whitish, concentric 

 lines, especially near the periphery ; pith flecks 

 (cross) usually large, conspicuous, 



Betula populifolia. 

 aa. Pores (cross) not visible nor conspicuous, even with magnifier, 

 i. e., wood composed mostly of one kind of cells (tracheids),. which 

 are uniform in structure and arranged in definite radial rows; resin 

 ducts and resin cells (cross) often present, especially in the summer 

 wood; rays (cross) never conspicuous. 



b. Resin ducts or resin cells or both (cross) present, the former 

 usually visible to the naked eye, the latter for the most part 

 prominent and more or less confluent, forming conspicuous tan- 

 gential lines; fusiform rays (tangential) present (absent in 

 J unip eru s znd Taxodium). 



c. Resin ducts and resin cells (cross) scattered, single or in 

 groups, but never forming tangential lines ; fusiform rays 

 {tangential) present; rays {radial) zvith tracheids. 

 d. Heartwood distinct in color from sapwood ; resin ducts 

 (cross) conspicuous, because of size or color, tJie epithelium 

 cells thin-walled; fusiform rays (tangential) broad and 

 prominent , usually zvith one to several large resin ducts, 

 e. Resin ducts (cross) few, widely scattering, without ty- 

 loses; resin cells (cross) present near the outer limit of 

 the summer wood; tracheids (radial) with occasional 

 spirals; heartwood light russet-brown, 



Larix lariclna, p. 219. 



ee. Resin ducts (cross) numerous, evenly scattered through 



the rings, zvith prominent tyloses; resin cells (cross) 



wholly absent ; tracheids (radial) zvholly zvithouf spirals; 



heartwood whitish, orange to reddish. 



