Pseudotsuga 815 



high elevations in the Rocky Mountains, through Montana, Colorado, Utah, Arizona, 

 New Mexico, and Mexico, is a smaller tree than the form which occurs in the moist 

 climate of the Pacific coast region. It bears small cones, 2 to 3 inches in length, 

 which in rare cases have the bracts reflexed, but resemble in all essential characters, 

 except size, the cones of the coast form. The leaves are usually thicker in texture 

 and are very glaucous beneath ; but the bluish tint visible on the upper surface 

 of the leaves, which is supposed to be characteristic, while common in certain 

 localities, and in others occurring on scattered individual trees, is no more constant 

 than the similar coloured variation which is met with in trees like Picea pungens and 

 Cedrus atlantica. Mayr has separated the Rocky Mountain form as a distinct 

 species, P. glauca ; but the differences, being rather physiological than morpho- 

 logical, do not entitle it to rank as more than a variety. The main difference lies 

 in the rate of growth and the hardiness of the tree, when seeds of it are raised in 

 countries remote from its native habitat. 



Dr. C. C. Parry discovered this variety of the Douglas fir in the outer ranges 

 of the Rocky Mountains in 1862 ; and in the following year seeds were sent to the 

 Botanic Garden of Harvard College, from which plants were raised, that have 

 proved perfectly hardy and vigorous in growth in New England. In the north- 

 eastern States the Pacific Coast form, whether introduced by seeds collected in 

 Oregon or produced by trees growing in England, has not proved hardy. 



The exact date of the introduction of the Colorado Douglas into Europe is 

 uncertain; but it appears to have been unknown in 1884, when the first edition of 

 Veitch's Manual was published, and was described as a distinct variety by Beissner 

 in 1891. Seeds were apparently sent from Mexico by Roezl in 1856, and plants 1 

 raised from these on the continent do not seem to differ from the Colorado Douglas. 



According to the experiments of Johannes Rafn, of Copenhagen, the germination 

 of the seed of Douglas fir from Colorado is quicker and much better than that from 

 the Pacific coast. 2 



In England young plants of the Colorado Douglas 3 have ascending branches, 

 and are more narrowly pyramidal in habit than the Oregon Douglas, which has 

 wide-spreading horizontal branches. Owing to its slowness of growth, the Colorado 

 variety has short internodes between the branches, which give it a bushy appearance. 

 The blue tint of the foliage can scarcely be relied on as a distinctive character, as it 

 is variable in intensity and often disappears with age. The leaves are usually 

 thicker, but do not differ in length or shape from those of the Oregon Douglas, the 

 sharp-pointed apex being characteristic of both forms in the young stage. The 

 young branchlets of the Colorado variety are often either quite glabrous or show only 

 a few minute hairs under the lens, whereas those of the other form are distinctly 

 pubescent. In wild trees, judging from herbarium specimens, this distinction does 

 not occur. 



1 Pseudotsuga Lindleyana, Carriere, raised from Mexican seed sent by Roezl, and P. glaucescens, Bailly, also probably 

 from Mexican seed, belong to var. glauca, and bear cones with strongly reflexed bracts. 



2 Trans. Roy, Scot. Arbor. Soc, xvi. 408 (1901). 



3 The Colorado Douglas in cultivation in England has been supposed by Schwappach (cf. Richardson in Trans. Roy. 

 Scot. Arbor. Soc. xviii. 195, with figure) to be Pseudotsuga macrocarpa ; but there is no evidence to support this opinion. 



