208 MISC. PUBLICATION 303, U. S. DEPT. OF AGRICULTURE 



Pseudotsuga douglasii, see Pseudotsuga taxifolia. 



Pseudotsuga glauca Mayr. T Colorado Douglas fir. 



P. douglasii glauca Mayr. 

 Range : 9, 11, 13, 14, 16. 

 Site : Well-drained, sun. 

 Fruit : Cone, available September-October. 



A large evergreen tree ; resistant to winter cold ; susceptible to spring frost ; 

 grows well on dry, sandy soil and moist loamy soil but not clay, gravel or poorly 

 drained sites ; slow growing ; wood much less valuable commercially than that 

 of P. taxifolia; does not pioneer in burns; shorter lived than P. taxifolia. 



Stomach records: Richardson's grouse; plains white-tailed deer, black-tailed 

 deer, mountain sheep. Observations: Captive sharp-tailed grouse, dusky grouse ; 

 red squirrel, chestnut-mantled ground squirrel, porcupine, bighorn. 



Pseudotsuga macrocarpa (Torr.) Mayr. Bigcone spruce. 



Range : 4, 5, 10. 

 Site : Dry, well-drained, sun. 

 Fruit: Cone; mature in August, seeds shed August-September, some 



cones persistent the year round. 



A large evergreen tree ; slow growing ; wood not used commercially ; seed 

 vitality low but persistent. 



Observations: Seeds eaten by rodents and birds. 



Pseudotsuga mucronata, see Pseudotsuga taxifolia. 



Pseudotsuga taxifolia (Lam.) Britt. Oregon Douglas flr. 



P. douglasii Carr., P. mucronata (Raf.) Sudw., P. douglasii caesia Schwerin. 

 Range : 1, 2, 3, 4, 5, 6. 

 Site : Well-drained, sun. 



Fruit : Cone ; mature September-October, seeds shed at once. 

 A very large evergreen tree ; demands high relative humidity for best growth ; 

 cannot withstand severe cold or drying winds ; grows best on well-drained, 

 sandy loam; absent from poorly drained areas; growth rate rapid; an ex- 

 tremely important timber tree ; often a pioneer in burns ; much larger and 

 longer lived tree than P. glauca. (See footnote under P. glauca.) 



Var. caesia Schwerin is a form more or less intermediate between this species 

 and P. glauca; it occurs in regions 6, 7, and 12 ; makes no summer growth and 

 is slower growing than the species. 



Observations: Dusky and Franklin grouse; browsed as a last resort by Olym- 

 pic wapiti; porcupine; much eaten by Douglas squirrel, Sierra chickaree, red 

 spruce squirrel, and Magdalena chipmunk ; of slight importance as browse for 

 mule deer. 



Psilostrophe cooperi (Gray) Greene. 

 Riddelia cooperi Gray. 

 Range: 9, 10, 11. 

 Site: Dry, well-drained, sun. 

 Fruit : Achenje. 

 A small, clump-forming shrub. 



7 The separation of the Rocky Mountain from the western form of the Douglas fir has 

 not commonly been made in this country, but there appears to be such a good basis for 

 this separation, not only ecologically but taxonomically, that it is here made. Reference 

 to Henry and Flood (278) and Frothingham (204) will show the following characteristics 

 to separate the two species: P. taxifolia (1) Rapid growing; (2) wide crown; (3) 

 produces a second leading shoot in summer and this late growth makes it susceptible to 

 injury by late frosts ; (4) foliage more regularly disposed in two ranks, soft to touch ; 

 (5) leaves thin, under surface flat, no idioblasts present; (6) leaves contain geraniol, and, 

 consequently, smell like pineapple; (7) young cones green to pink, bracts erect; (8) cones 

 3 to 4 inches long; (9) wood straight, light, durable, excellent timber; (10) torus of 

 bordered pits centrally placed, wood readily permeated by creosote; (11) germination of 

 seed poor; (12) attacked by Uhermes; (13) growth rate twice that of the other species, 

 timber yield 4 to 10 times that of the other; (14) will grow in England but not New 

 England. P. glauca (1) Less rapid growing; (2) crown narrow, compact, pyramidal; 

 (3) does not produce a second leading shoot, growth completed early in the season, and, 

 consequently, not susceptible to frost ; (4) foliage less regularly disposed in two ranks ; 

 (5) leaves thick, under surface convex, idioblasts present: (6) leaves contain bornyl ace- 

 tate and, consequently, smell like turpentine ; (7) young cones brilliant red, bracts 

 spreading and reflexed ; (8) cones 2 to 3 inches long; (9) wood irregular in structure, 

 strong and durable, rough timber; (10) torus of bordered pits pressed to one side, wood 

 not readily permeated by creosote; (11) germination of seed much better and sooner than 

 the other species; (12) not attacked by Chermes; (13) growth rate about half that of 

 the other species, timber yield much less than that of the other species; (14) will not 

 grow in England, but will grow in New England. 



