THE SPECIES. 49 



ing position on the twig by the torsion of their short stems. The 

 twigs also have a habit of spreading horizontally, and those which 

 originate above or below bend into a horizontal position to conform 

 with the rest. The cones of the grand fir are green at maturity, 

 about 3 or 4 inches in length and 1 inch or more in thickness, com- 

 posed of broad, closely overlapping scales. The bark of this species 

 is smooth in youth, but gradually it becomes broken by furrows, 

 which deepen with age ; in old trees the bark is about 2 inches thick, 

 with uniformly narrow ridges and deep grooves, grayish on the 

 surface, but a deep brick-red within. 



The alpine fir (Abies lasiocarpa) , often called balsam fir, in Mon- 

 tana is more common. It is not the true balsam fir, however, as that 

 species is a native of the northeastern part of the continent and dif- 

 fers from this in some very important features. The range of the 

 Alpine fir extends from Alaska to Alberta in the north, and south- 

 ward through the Cascades to California and in the Rocky Moun- 

 tains to Arizona and New Mexico. In Montana it is common on all 

 the higher altitudes, not only of the main but also of the outlying 

 ranges. In some places it occurs as low as 2,000 feet, as in the north- 

 western part of the State, along the Kootenai River, but for the most 

 part it occurs from 5,000 feet up to timber line, where it is mixed 

 with Engelmann spruce and whitebark pine. 



One of the striking features of this tree is its form, by which a 

 normal specimen can be distinguished as far as it can be seen. Its 

 typical shape is that of a very narrow spire. It seldom has much 

 clear length, owing to its habit of growing in open groups. The 

 bark is smooth, seldom rough, even in old specimens. The leaves are 

 shorter and darker colored than those of the grand fir. The cones 

 are oblong, dark purple, and 1J to 3 inches in length. This tree 

 may attain, under the best conditions, a height of 150 feet and a 

 diameter of 3 or more feet. Owing to its usual inaccessibility and 

 its inferior form, the alpine fir is of no importance commercial^. 



ARBOR VITAE. 



The arbor vitse is commonly called a cedar, although that 

 appellation is applied to several other genera as well. Two species 

 of this genus occur in North America, one on the Atlantic, the other 

 on the Pacific coast. They are trees which endure shade, require a 

 good deal of moisture, and a moderately cool climate. 



In all of the preceding genera the leaf arrangement is alternate 

 or spiral; in the arbor vitse and juniper the arrangement is oppo- 

 site or cyclic. This applies to the cone members as well as to the 

 leaves. The stem of the arbor vitae is a straight central shaft, ex- 

 tending through the crown. The branches droop conspicuously, and 



