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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 fungens 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? 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.’
In England young plants of the Colorado Douglas* 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, Carriére, raised from Mexican seed sent by Roezl, and P. glaucescens, Bailly, also probably from Mexican seed, belong to var. g/auca, 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.