PRACTICAL STUDY OF PLANT FORMATIONS. 643 



turnip, etc., are cultivated, while orchard crops like apples, peaches, 

 cherries, pears, plums, and a variety of berries are common. 



b. The Arid Transition Area. "The western or arid division of the Tran- 

 sition zone comprises the western part of the Dakotas, northern Montana 

 east of the Rocky Mountains, southern Assiniboia, small areas in Mani- 

 toba and Alberta, the higher parts of the Great Basin and the plateau 

 region generally (except the boreal mountain areas), the eastern base of 

 the Cascade-Sierra system, and local areas still farther west, jn Oregon 

 and California, where it merges into the humid Pacific Coast division." 

 The prevailing type of vegetation is the true sage-brush (Artemisia tri- 

 denta) with extensive tracts of the yellow or bull pine. Wheat, oats, 

 barley, corn, apples, cherries, grapes, pears, plums, potatoes, sugar-beets, 

 etc., are cultivated. 



c. The Pacific Coast Transition Area. "The humid Pacific Coast divi- 

 sion of the Transition zone comprises the western parts of Washington 

 and Oregon between the coast mountains and the Cascade Range, parts 

 of northern California from near Cape Mendocino southward to the Santa 

 Barbara Mountains. To the south and east it passes into the Arid Tran- 

 sition, and in places into the Upper Sonoran." This region, as a whole, is 

 one of great humidity. "The northern and more humid part is covered 

 by a magnificent coniferous forest, carpeted with moss and ferns, and 

 often choked with undergrowth. The prevailing trees are Douglas fir, 

 Pacific cedar, western hemlock, and Sitka spruce, whose majestic trunks 

 attain an average height of more than 200 feet. There are also many 

 broad-leaf maples, tree-alders, madronas and western dogwoods, and 

 numerous kinds of shrubs," as sabal (Gaultheria shallon), thimble-berry 

 (Rubus nootkanus), Oregon grape (Berberis nervosa), and devil's-club 

 ( Echinopanax horridula) . 



"The region as a whole is one of relatively uniform temperature, the 

 wide seasonal differences usual in other parts of the Transition zone being 

 unknown. The temperature of the summer season, the hottest part of the 

 year, is phenomenally low for the latitude, enabling northern or boreal 

 types to push south as far as latitude 35. On the other hand, the summer 

 season is so prolonged (from the standpoint of temperature) that the total 

 quantity of heat for the entire season is phenomenally high for the Latitude, 

 enabling southern or austral species to push north as far as Puget Sound, 

 where the total quantity of heat is even greater than at Philadelphia, Pitts- 

 burg, Cleveland, and Omaha, although Puget Sound is 500 miles north 

 of the latitude of these places. Even at Cape Flattery the extreme north- 

 western point of the United States which is exposed throughout the year 

 to the cold coast fogs, the total quantity of heat is 500 F. greater than 

 at Eastport, Maine, although the latter is the more southern locality and 

 has the higher mean summer temperature. The low summer temperature 



