314 GEOGEAPHICAL DISTRIBUTION OF PLANTS. 



formed sandbanks of the. rivers up to the 68th parallel, its 

 flexible, densely growing young stems serving to arrest the 

 mud, and speedily to raise the bank above the ordinary level of 

 the water. In drier spots, by river banks in the Saskatchewan 

 basin, it forms bushes from 20 to 25 feet in height. Even 

 in the passes of the Rocky Mountains, as at Jasper Lake, it 

 grows freely on drifting sands. Lieut. Abert found it growing 

 at Council Grove, and Hundred-and-ten-mile Creek, at the height 

 of 1,200 feet above the sea, between the 38th and 39th parallels. 

 It inhabits also the banks of the Susquehannah, and all the 

 Northern States. The soft pliable twigs are a favoux-ite food of 

 the moose-deer, and might, indeed, as they grow on the flooded 

 sandbanks, be mowed like hay. Populus balsamifera, balsam 

 poplar, or tacamahac, was found growing on the banks of the 

 Mackenzie up to lat. 59°, where it makes a very slender tree. 

 In the southern part of the delta of that river it forms groups 

 of healthy young trees, and from thence to the United States it 

 flourishes on rich alluvial and occasionally flooded banks of rivers 

 to the exclusion, on such spots, of most other trees : its trunk 

 attains a greater circumference than any other member of the 

 northern forest, but its wood is of no value, except for fuel ; and, 

 when old, the tree is unsightly from having very generally lost 

 its top. Its growth is rapid, and its decay apparently equally so. 

 I measured some drift logs of this tree which were floating 

 down the Mackenzie, and found them to be about 15 feet in 

 circumference, with a very moderate tapering upwards. The 

 Crees name it Mathch-metus, or ugly poplar. Dr. Asa Gray 

 gives as its southern limit New England, Wisconsin, and per- 

 haps Pennsylvania, but not further. It crosses Beering's Sea 

 to Kamtschatka ; and on the rivers of Oregon it grows, ac- 

 cording to Douglas, to the height of 140 feet, and 20 feet in 

 diameter. P. candicans, balm of Gilead, which greatly resem- 

 bles the preceding, has not been detected north of Wisconsin : 

 it is the common balsam poplar of Pennsylvania, New York, 

 and New England. P. monilifera, Icevigata vel canadensis 

 (Mx.), is a more southern species, being rare in New England, 

 but taking the place of P. candicans in Western Pennsylvania, 



