GEOLOGICAL AND GEOGRAPHICAL DISTRIBUTION 547 



barren throughout most of its extent, and with its most conspicuous 

 plant the fantastic Tree-yuccas (PI. XIII), which occur in scattered 

 groves in a few places. Any more absolute contrast between the 

 eastern and western ends of the journey it would be hard to imagine. 



The Flora of the Pacific Coast 



The distribution of the plants upon the Pacific coast, especially in 

 California, offers most interesting problems to the student of phyto- 

 geography. Owing to the equalizing influence of the Pacific, and 

 the position of the mountain ranges, the climate of the whole Pacific 

 coast is extremely equable, luxuriant forests extending northward in 

 Alaska to about latitude 60. At Sitka, in latitude 57, extreme cold 

 is unknown, and the annual precipitation is nearly 250 centimetres, 

 so that the vegetation is almost tropical in its luxuriance. Spruce, 

 Hemlock, and Cedars, 30 to 50 metres in height, and with trunks 2 

 to 3 metres in diameter, are met with, and the ground is covered with 

 an impassable thicket of shrubs and herbaceous plants. Many of 

 these are northern types common to the whole sub-arctic zone ; but 

 others are evidently of Asiatic origin, and do not occur away from 

 the Pacific coast. The commonest tree, the Sitka-spruce (Picea 

 Sitchensis), is said to occur also on the northeast Asiatic coast, and 

 a number of herbaceous plants are also Asiatic. Of the latter, the 

 most conspicuous is the common Aroid (Lysichiton Kamtchatcense), 

 which resembles somewhat the Skunk-cabbage of our Eastern states. 

 Another Asiatic plant is Fritillaria Kamtcliatica, belonging to a 

 genus which occurs in America only on the Pacific slope. 



The whole coast, as far south as Puget Sound, is covered with an 

 extraordinarily heavy forest of coniferous trees which often come 

 down to the water's edge. While at the far north the Spruce and 

 Hemlock predominate, in British Columbia and Washington the 

 Douglas Spruce (Pseudotsuga Douglasii) is the predominant tree. 

 Here it attains a height of 100 metres or more, and forms the most 

 important timber tree of the region. 



Most of the herbaceous plants of this region are allied to the 

 common northern species, and in many instances are identical ; 

 but there is a mingling of forms not found farther east, such as 

 Lysichiton. Violets, Trilliums, Dicentras, White Clover, much like 

 those of the Northeastern states, are common, and the general 

 aspect of the woodland flowers resembles that of northern Michigan, 

 or the Adirondacks. 



The high mountain ranges of the northern Pacific coast are continued 

 southward into California, where they divide into the Sierra Nevada 

 and the series of Coast ranges. The rainfall diminishes rapidly 

 southward, and most of California has an absolutely rainless summer. 



