THE FOREST COMMUNITY. 



105 



are rebranched much after the fashion of the main roots already described. 

 As the main roots and these larger branches approach their extremities, they 

 are divided several times so as to form fairly well-branched termini. 



Arctostaphylos uva-ursi. — This ericad, which is the typical undershrub of 

 the pine forest, also occm's rather abundantly in the more open portions of the 

 Douglas fir forest, where it forms great mats covering areas of many square 

 meters. Its xerophytic qualities are shown by its frequent appearance in the 

 half-gravel-slide community. A very elaborate and well-developed root 

 system arises from the woody prostrate stems, which vary from a few milli- 

 meters to 3 cm. in diameter. While some of the roots reach a maximum depth 

 of from 40 to 46 inches, the major portion of the absorbing system lies in the 

 first 18 inches of soil. From the base of the prostrate stems as well as from 

 numerous shallow horizontal roots arise great numbers of rootlets only 1 to 2 

 mm. in diameter and from 4 to 8 inches long, but so abundantly supplied with 

 masses of branched and rebranched laterals that they fill the surface soil with 

 a network of roots. In addition to these, larger branches, sometimes even a 

 centimeter in diameter, run off at all angles from the horizontal to vertically 

 downward, pursuing tortuous courses and branching and rebranching freely. 

 They attain a length of 3 or 4 feet and end at depths varying from a few 

 inches to more than 3 feet. The branches from these as well as the ends of 

 the main roots themselves form great mats of well-developed rootlets in the 

 crevices of the gravelly soil. Plate 28, a, shows something of the extent and 

 abundance of these branches. 



Senecio cernuus. — ^This herb is abundant in the fir forest. The root system 

 consists of a group of from 8 to 20 white, somewhat fleshy roots. At their 

 point of origin they vary from less than 0.5 mm. to 2 or 3 mm. in diameter. 

 Relatively few of these penetrate the soil in a vertical or slightly oblique 

 direction to a maximum distance of 12 to 15 inches. By far the greater part 

 of these roots take a course practically parallel with the surface at a depth of 

 from 1 to 3 inches — ^in fact, many of them run just below the surface accumu- 

 lation of duff and semi-decayed leaves ; others may take a slightly more down- 

 ward course and end at a depth of from 4 to 8 inches below the surface. The 

 maximum spread of these horizontal roots may vary from a few inches to 18 

 or 25 inches. Throughout their course the main roots are fairly well supplied 

 with laterals varjdng in length from a centimeter or less to 6 or 8 inches. 

 These in turn may be branched again to the second and third order, so as to 

 form a very efficient surface system well adapted to absorb the shallow water- 

 content resulting from the frequent mountain showers. Eight plants were 

 examined (fig. 48). 



Castilleia miniata. — This plant is a conamon component not only of grassy 

 half-gravel-slides, but it also occurs rather abundantly in the fir forest. Rela- 

 tive to the size of the plant it has a very meager root system. This consists 

 of 5 to 20 main branches, varying in size from 1 to 3 mm. These all show a 

 strong tendency to spread out laterally and run off in the surface soil, usually 

 at a depth not greater than 5 to 6 inches to distances of 12 to 18 inches or less. 

 No roots were found penetrating deeper than 8 inches. While these rather 

 coarse, yellow, brittle roots are fairly well branched, they are only poorly 

 supplied with fine absorbing laterals as compared with other plants examined 

 in this community. 



Heuchera parvifolia. — This plant is fairly abundant in the Douglas fir 

 forest. It has a strong tap-root, sometimes as large as 15 mm. in diameter. 

 However, this tapers so rapidly that within a distance of 6 to 8 inches it is 



