42 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



flowered currant {Ribes sanguineum). By this time the Scoiiler wil- 

 low is conspicuous, and in wet places the red alder (Alnus oregana). 

 These two trees dominate the vegetation until the young red firs 

 which spring up in a very dense growth have become large enough 

 to supersede them. The red fir is so completely the dominant tree 

 in the region that as a rule it quickly reforests itself whenever 

 destroyed. 



BOTTOM LANDS. 



The bottom lands of western Washington are mainly river valleys. 

 Less commonly they occur about lake borders or form marshes. The 

 commonest type of forest covering is a red alder and giant cedar asso- 

 ciation, which, hoAvever, is seldom pure. Rarely either one of these 

 trees may occupy the ground exclusively. Usually, however, there arc 

 associated various other trees, as white fir {Abies grandis), large- 

 leaved maple {Acer macrophyllum) ^ Oregon ash {Fraxhms oregana), 

 and Cottonwood {Populns tnchocarpa.) The cottonwood often foruis 

 groves of pure growth in the river valleys, and the maple does so 

 occasionally. Moisture of the soil is apparently the one factor that 

 favors the red alder-cedar association, which is quite as common on 

 springy hillsides and upland swamps as in river valleys. Wliere the 

 amount of soil moisture is not too great the red fir occurs sparingly, 

 but the individuals are often of gigantic size. In bottom lands that 

 are excessively wet, the alder is absent and often the cedar also. Such 

 lands commonly are covered by dense thickets composed of various 

 species of willows, western cornel {Comus occidentalis), crabapple 

 {Pyrus diversifolia), and vine maple {Acer circinatum) . These same 

 species form the usual fringe along the banks of small streams flow- 

 ing through the forest, especially the cornel and the vine maple. In 

 such situations occur also various shrubs, as the devil's club {Echino- 

 panax horridum) which, contrary to the oft-told tale, seldom forms 

 dense thickets, the salmon berry {Rubus speetabilis), the fetid currant 

 {Ribes bracteosum), and the red-berried elder {Sambucus callicarpa). 



GRAVELLY PRAIRIES. 



The soil of these prairies, which are comparatively limited in 

 extent, consists mainly of fine water-worn gravel, the pebbles mak- 

 ing up perhaps 50 per cent, or more, of the soil. The prairies com- 

 monly present the appearance of a sterile pasture (PI. IX) with scat- 

 tered oaks {Quercus garryana) here and there, and occasional beauti- 

 fully symmetrical young trees of red fir. At the edges of the prairie, 

 where the gravelly soil ceases, a dense forest of red fir usually occu- 

 pies the ground, the gravelly prairie soil serving as an almost perfect 

 barrier to this tree. In a few localities, where the gravelly soil 

 merges gradually into the ordinary loams or clays of the region, the 



