TSUGA 265 



walls medium, unequal, very sparingly pitted, in the summer wood 

 becoming conspicuously thicker and strongly pitted ; the terminal 

 walls coarsely pitted, when seen in plan like a sieve plate ; the lateral 

 walls with obscurely bordered pits, 1-4, or in the marginal cells and 

 low rays upwards of 6, per tracheid, becoming reduced toward the 

 summer wood, where they are only i or entirely wanting. Bordered 

 pits numerous, elliptical, usually less than half the tracheid, in i row 

 or often in pairs and imperfectly 2-rowed. Pits on the tangential 

 walls of the summer tracheids not very numerous, rather small. 

 Resin cells and resinous tracheids wanting. 



Tangential. Rays medium to high, sparingly resinous, narrow, strictly 

 i-seriate ; the cells uniform, oblong, rarely oval. 



13. TSUGA, CARR. PLATES 44 AND 45 



Transverse. Growth rings usually thin, the summer wood prominent, usu- 

 ally dense. Resin passages rarely present (T. heterophylla) and 

 then imperfectly organized. Resin cells scattering on the outer face 

 of the summer wood and distinguished by (i) their resinous contents, 

 (2) their somewhat advanced position, (3) their thinner walls, and 

 (4) the sieve-plate structure of the terminal walls ; rarely numerous 

 and zonate in the spring or summer wood. Resinous tracheids wanting 

 (except in T. Mertensiana). 



Radial. Ray tracheids usually prominent, sometimes interspersed, usually 

 marginal. Ray cells usually resinous, more or less contracted at the 

 ends, the terminal walls strongly pitted. Tracheids wholly without 

 spirals. 



Tangential. Fusiform rays wholly wanting. Ray cells rarely in pairs, not 

 broad, chiefly oval or round. 



* 

 SYNOPSIS OF SPECIES 



Bordered pits in 2 rows. 



Resin passages wholly wanting, the prominent resin cells scattering 

 on the outer face of the summer wood. 



Pits on the lateral walls of the ray cells 2-4, or in the summer 

 wood 1-2, per tracheid. 



i. T. canadensis. 

 Bordered pits in i row. 



Resin passages present but imperfectly formed, in more or less con- 

 tinuous series, the resin cells scattering on the outer face of the 

 summer wood. 



Pits on the lateral walls of the ray cells 1-2, rarely 3, per 

 tracheid. 



Spring tracheids very large and uniform, distinctly 4-sided, 



the walls thin. 



5. T. Mertensiana. 



