64 JOURNAL OF THE ARNOLD ARBORETUM [vol. i 



This variety of the Canoe Birch differs from the tyi>e in the sHghtly cor- 

 date or rounded base of the leaves whicli are acute on the type specimen but 

 are as often acuminate or abruptly acuminate as acute; the spreading teeth 

 of the leaves, which have been used to distinguish this tree, more often point 

 forward and appear to have no specific importance. The biirk separates in 

 thin layers and is usually white but is sometimes on occasional trees dark 

 red-browTi or orange color. 



This is the common White Birch of the northern Rocky Mountain region 

 from Alberta to northern Montana and Idaho, and westward to eastern 

 Washington, Oregon and British Columbia where it grows witli the var. oc- 

 cidentalis Sarg. from which it dlifers cliiefly in its smaller leaves subcordate 

 or rounded at bjise, and its usually smaller strobiles. The leaves of the var. 



occidental^ Sarg. are rounded or cuneate at ba^se, and onh' rarely cordate 



usually only on vigorous shoots. 



'/. 



and its viirietlcs, differs on different individuals from white to reddish 

 brown and to orange color. 



Much reliance has been placed on the color of the bark for distinguishing 

 species among the Canoe Birches which cross the continent in the north, 

 but late colkvtions indicate that this character cannot be depended on. 

 The pubescence on the leaves and branchlets do not furnisli si)ecific char- 

 acters in tliis group, and the shai)e of the scales of the mature strobiles, 

 which usually vary in all species of Betula, cannot be used to separate 

 successfully the different varieties of the Canoe Birch cO-s here considered. 



Betula papyrifera var. montanensis, n. var. — B. moiitancnsis Butler in 

 Bull. Torrey Bot. Club, xxxvi. 439, f. 17 (1909). 



From other forms of Betula papyrifera this variety differs in its thicker, 

 darker green leaves and in the unusually long base of some of the mature 

 scales under the nutlets which below the middle of the strobile is rather 

 more than twice the length of the exijanded upper part of tlie scale, while 

 near the apex of the strobile it is only about as long. The leaves of the 

 type of /?. viojittuien^'ib- from Yellow Bav on the eastern shore of Flathead 

 Lake, IMontana, arc represented as broadly ovate, truncate at base and acute 

 at apex; and the bark of this tree is described as of the same bronze color as 

 that of B. occidentalin but '' is dull, never peeled, and is always mottled with 

 gray." What is evidently the same variety was collected by J. G. Jack 

 Sej)tember 13, 1919, at Sandpoint, Bonner County, Ididio, where close to 



the railroad station are growing a number of trees 14-17 m. tall with white 

 bark. On one of the two branches collected by Mr. Jack the leaves resemble 

 exactly the leaf of B. montanensis as figured in the Bull. Torrey Bot. Club, 

 but on the fruiting branch of the same tree the leaves are all coarsely doubly 

 serrate, long-i)ointed and acuminate, and vary from l)road-ovate with a 

 rounded base to oblong-ovate or IanfHH>late, and narrowed and rounded at 

 base, and are KM 2 cm. long and 4-5 cm. wide. The branchlets during the 

 first season are puberulous. In the stoutness of the mature catkins and 

 in the shape of their scales, and in the shape and thickness of the leaves 

 this appciu-sthe most distinct of the different forms of the Canoe Birch. 



