LIST OF TREES AND SHRUBS. 315 



Ohio, and Kentucky. Ikgrows on the banks of the Arkansas 

 and other southern tributaries of the Missouri. P. tremuloides, 

 aspen. Dr. Gray believes that, south of Pennsylvania and 

 Kentucky, this tree is confined to the Alleghanies, and even 

 on these mountains it is rare. In the Northern States it is 

 common, and varies in height from 20 to 50 feet. It abounds 

 in Rupert's Land in the more fertile soils, and very generally 

 springs up in place of the white spruce, when that tree has 

 been destroyed by fire. Its range is co-extensive with the 

 forest land ; but towards the Arctic Sea, and in lat. 69° on the 

 Mackenzie, it is a slender willow-like tree. It is the best fire- 

 wood in the country, but is applied to no other economical 

 purpose, except that its ashes are collected on account of the 

 abundance of potash they contain. It do not know whether it 

 inhabits the Pacific coasts or not. P. grandidenta, big-toothed 

 aspen, is common in the Northern States, and reaches New 

 Brunswick and Canada, but did not come under our notice on 

 the canoe route. 



Peatanace^e. — Platanus occidentalis, American Plane-tree, 

 resembles the well-known P. orientalis in the way that its ex- 

 terior bark falls off in thin plates. It extends northwards to 

 Canada, but does not appear north of Lake Superior. 



Conifers. — Pinus banksiana, gray pine, the Cypres of the 

 voyagers, grows from the arctic circle on the Mackenzie, dow r n 

 to the great Canada lakes, south of which, Dr. Gray has scarcely 

 seen it, but has heard that it is found in the northern districts 

 of Maine ; and it occurs in the list of Wisconsin plants pub- 

 lished by the American Association. It crosses the Rocky 

 Mountains to the Spokan River in latitude 47° north. This 

 would be an ornamental tree on many sandy and otherwise 

 unproductive wastes. P. resinosa, red pine, has its southern 

 limit, according to Emerson, at Wilkesbarre, in Pennsylvania 

 (latitude 411° north). I have traced it to 56±° of latitude 

 on Methy River, and it crosses the Rocky Mountains to lati- 

 tude 43° in Oregon. Dr. Gray says that its height in the 

 northern states is from 60 to 80 feet, and Emerson relates 

 that a few years ago it was not uncommon to find trees 



