538 RELATION TO ENVIRONMENT. 



times was slight, and the vegetation retarded the flow of water to 

 a much greater extent than on a more pronounced incline. This, 

 together with the effect of the sands in damming up to some extent 

 the flow, has produced the conditions which have made this great 

 swamp possible. Some of the characteristic vegetation growing 

 in the area is especially effective in retarding the flow of the 

 drainage water from the surface and higher elevations, the cane 

 (Arundinaria), the bald cypress, the tupelo gum, in some places 

 the mangrove, etc. The bald cypress in wet ground develops 

 numerous erect "knees" (fig. 4980) from the roots, which serve 

 the purpose of aerating the root system, and they also catch 

 floating material. 



1019. Forests of the Pacific transition area. This is a majes- 

 tic coniferous forest, in parts of Washington, Oregon, and Califor- 

 nia, due to the unusual conditions which prevail. The annual 

 rainfall is very heavy. The principal trees are the Douglas fir, 

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

 gain an average height of more than 200 feet. Altogether in 

 Washington and Oregon there are 27 different species of conifer- 

 ous trees. Some of those not mentioned above are the western 

 white pine, the giant redwood, and the Big trees of California. 

 Broad-leaved trees, as maples, birches, oaks, aspens, alders, madro- 

 nas, western dogwoods, and different kinds of shrubs, many of 

 them reaching the size of small trees, occur as undergrowth which 

 often chokes the interior of the forest, while the forest floor in 

 many places is carpeted with mosses and ferns. 



1020. The redwood (Sequoia sempervirens) reaches a greater 

 height than any other American tree,* but does not attain the 

 age of the Big tree of the Sierra Mountains in California. The 

 redwood is confined to a "narrow strip of the coast ranges 10 to 

 30 miles wide extending from the Bay of Monterey, Cal., to a 

 short distance across the southern border of Oregon." On 

 mountain slopes it reaches a maximum height of about 225 feet 

 and 10 feet in diameter, while in the valleys, where soil and moist- 



* According to R. T. Fischer. 



