i'OO Pub. Puget Sound Biol. Sta. Vol. 2, No. 46 



thing but fungi. The warmth and moisture of autumn in the Puget Sound 

 region greatly favor the growth of these plants. 



There are four distinct plant associations in this area. In the cen- 

 tral portion of the area, approximately at its lowest point is an open por- 

 tion containing a few vigorous bunches of sedge. The remainder of this 



PLATE 29 



Diagram of plant associations in the Covington depression: a, Carex- 

 Sphagnum; b, Spiraea-Sphagnum; c, Populus-Polytriclium; d, Pseudotsuga- 

 Gaultheria. 



zone had no vegetation, except a thin but continuous carpet of Sphagnum 

 and an occasional mushroom. This is designated as the Carex-Sphagnum 

 association on the accompanying diagram. By far the larger portion of 

 the depression is covered with a dense growth of hardback (Spiraea doug- 

 lasii). These bushes are mostly from 1.5 to 3 meters (5 to 10 feet) high 

 and grow so close together that it is difficult for one to make his way 

 through the dense thicket that they form. This shrub is quite charac- 

 teristic of swamps and of the marginal ditches of bogs in the Puget Sound 

 region. It flourishes well where the soil is covered with water much or 

 even all of the time. Its stems have a tendency to become prostrate, and 

 when this occurs they send up new erect branches in great numbers, thus 

 forming a dense tangle of woody stems. It is thus well fitted to continue 

 its growth into a swamp. Since a dense growth of Sphagnum covers the 

 ground thruout this zone in this depression it may be called the Spiraea- 

 Sphagnum association. While the hardback thicket is continuous over the 

 larger part of this zone, there are occasional openings in it. The growth 

 of Sphagnum was more vigorous in these openings than in the thicket. The 

 Sphagnum everywhere covers the prostrate hardback stems and extends 

 15 to 25 cm. (6 to 10 inches) up the bases of the erect stems. In many 

 cases it has formed little mounds 10 to 20 cm. (4 to 8 inches) high over 

 stubs of broken hardback stems. A few mushrooms were found in this 

 zone also. On a few slightly elevated areas in the less dense portions of 



