[PENH allow] N. AMERICAN TAXACE^ AND CONIFERS 53 



9. PsEUDOTSUQA, Carr. 



Transverse. Growth -rings and summer wood very variable. Eesin-pas- 

 sages present and usually without thyloses, but with thick-walled 

 epithelium. Eesin-cells more or less numerous on the outer face of 

 the summer wood. 



Badial. Eay tracheids present. Eay-cells straight or contracted at the 

 ends ; the terminal walls thick and more or less coarsely pitted. 

 Wood tracheids with rather close spirals. Pits on the tangential 

 walls of the summer wood only. 



Tangential. Fusiform rays present, generally narrow, the central tract 

 of one small resin-passage without thyloses, but with small, thick- 

 walled epithelial cells. 



Species. 

 1. P. Douglasii, Carr. 



" " var. macrocarpa, Engel. 



10. Larix, Tourn. 



Transverse. Summer wood prominent, usually dense ; the transition 

 from the spring wood more or less abrupt. Eesin-passages without 

 thyloses, but Avith thick-walled and small but conspicuous ej^ithelial 

 cells. Eesin-cells rather frequent but scattering, on the outer face 

 of the summer wood. 



Radial. Eay tracheids prominent. Eay-cells contracted at the ends, 

 the upper and lower walls thick and entire or distinctly pitted ; the 

 lateral walls with simple or bordered pits ; the terminal walls thick 

 and strongly pitted. Tracheids wholly without spirals. 



Tangential. Fusiform rays prominent, usually high and narrow ; the 

 cells small and thick-walled ; the central tract small, and in branches, 

 often more or less completely obliterated. A well-defined genus, at 

 once distinguished bf the narrow and often high fusiform rays, and 

 the resin-cells scattering on the outer face of the summer wood. 



Species. 



1. T. occidentalis, Nutt. 



2. L. aviericana Michx. 



3. L. Lyalli, Pari. 



11. PiCEA, Link. 



Transverse. Growth-rings either broad or narrow. Transition from the 

 spring to the summer wood gradual. Eesin-passages with or with- 

 out thyloses, but with thick-walled ei^ithelial cells conspicuous. 

 Eesin-cells wholly wanting. 



Radial. Eay tracheids conspicuous, narrow, Eay-cells contracted at 

 the ends or straight, the terminal walls strongly pitted. Wood 

 tracheids wholly without sjMrals. 



