100 



THE ECOLOGICAL RELATIONS OF ROOTS. 



VIII. THE FOREST COMMUNITY. 



A forest community finally occupies the half -gravel-slide. It is 

 represented by Pinus ponderosa or Pseudotsuga mucronata, both of 

 which are frequently preceded by a chaparral stage. Along the 

 streams and moister slopes, Douglas fir meets the Engelmann spruce, 

 Picea engelmanni, with which it often forms a mictium. A rather large 

 number of herbs and undershrubs characteristic of the more mesophytic 

 type of forest were examained (plate 27, a, b). 



Pirola chlorantha. — ^This evergreen herb is very abundant and foiins 

 extensive clans on the floor of the spruce forest. The clusters of leaves arise at 

 intervals from a few inches to more than a foot from the glistening white 

 underground stems. These vary from 1 to 3 mm. in diameter, branch freely, 

 and form a connecting system for the individual plants. They lie at a depth 

 varying from 0.5 inch to about 5 inches. Just before the rootstock approaches 

 the surface to send up a cluster of leaves, it invariably branches, the branch 

 continuing to the next plant, etc. The root system is very meager and con- 

 sists of brownish roots arising at irregular intervals, usually about 1 inch apart 

 on the horizontal rootstock, although it is not unusual to find several inches of 

 the rootstock practically free from rootlets. These roots penetrate the moist 

 duif and rich humus soil to a depth of only 6 to 10 inches; while many of them 

 are only 1 to 1.5 inches long, others form brush-like clusters 3 to 5 inches in 

 length (fig. 42). 



Fig. 42. — Pirola chlorantha. 



Thalictrum fendleri. — This polydemic ranges in habitat from the half- 

 gravel-slide, into which it has worked its way from the bordering woodland, 

 to dense spruce forest. In the Douglas fir forest it forms extensive societies. 

 The plants here described were examined in a spruce forest. The slender 

 tops of these plants arise from a meager system of rhizomes almost black in 

 color, from 0.5 to 2 mm. in diameter, and seldom over 6 to 8 inches long. 

 The root system springs from the rhizome near the base of the erect stems, 

 sometimes as many as 30 or more fibrous roots originating from the base of a 



