CUPRESSUS 231 



Tracheids of the spring wood squarish-hexagonal. 

 Bordered pits round, distant, in i row. 



13. C. pulchellum. 



14. C. arkansanum. 



Bordered pits large, in i row, often in pairs, the latter sometimes so 

 approximated as to make the pits more or less 2-rowed. 



Pits on the lateral walls of the ray cells 1-2, in vertical series, or 

 in marginal cells and low rays 4, per tracheid. 



15. C. Dawsoni. 



Pits on the lateral walls of the ray cells obliterated. 



16. C. Wardi. 



Pits on the lateral walls of the ray cells minute, round. 



Medullary rays (tangential) small, the cells small, oblong, 

 15-iyx 10 p.. 



17. C. columbianum. 

 Bordered pits conspicuously in 2 rows. 



Pits on the lateral walls of the ray cells obliterated. 

 Growth rings obscure. 



1 8. C. elongatum. 

 Growth rings sharply denned. 



Tracheids of the earlier spring wood very large and 

 thin-walled. 



19. C. glasgowi. 

 Bordered pits in 2, or sometimes 3, rows. 



Pits on the lateral walls of the ray cells with large, oval pits 

 1-3 per tracheid. 



20. C. McGeei. 



Pits on the lateral walls of the ray cells 3 per tracheid. 



21. C. Calli. 



A. CHA1VLECYPARIS 



1. * C. thyoides, Linn. 



White Cedar 



Transverse. Growth rings thin, variable, the structure open throughout. 

 The summer wood chiefly thin, of 2-6 tracheids, the transition to the 

 spring wood rather abrupt, or sometimes thicker and not clearly sepa- 

 rable from the spring wood. Spring tracheids large, conspicuously 

 squarish, uniform, in regular rows, in small stems and branches often 

 much elongated radially, the walls not very thin. Resin cells widely 

 scattering and often apparently wanting ; when in bands, often giving 

 the appearance of secondary growth rings, chiefly in or near the sum- 

 mer wood. Medullary rays not very prominent or resinous, i cell 

 wide, distant 2-12 tracheids. 



