208 MISC. PUBLICATION 303, U. S. DEPT. OF AGRICULTURE 
Pseudotsuga douglasii, see Pseudotsuga tazvifolia. 
Pseudotsuga glauca Mayr.’ Colorado Douglas fir. 
P. douglasii glauca Mayr. 
Range: 9, 11, 18, 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. tazifolia. 
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 tavifolia. 
Pseudotsuga taxifolia (Lam.) Britt. Oregon Douglas fir. 
P. douglasii Carr., P. mucronata (Raf.) Sudw., P. douglasii caesia Schwerin. 
mansesle 324: 
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: Achene. 
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. tazifolia—(1) Rapid growing; (2) wide crown: (3) 
produces a second ieading 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, smeil 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 Chermes; (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. glawca—(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 haif 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. 
