104 



THE ECOLOGICAL RELATIONS OF ROOTS. 



not unlike that of Corylus (page 30). Two plants, 5 and 12 years old respectively 

 and about 3 feet high, were examined in the Douglas fir forest. From the base 

 of the clump prostrate stems about a centimeter or less in diameter run 

 horizontally just beneath the surface, or at least at a depth of only a few 

 inches, to distances of 2 or 3 feet, where they give rise to new plants. The 

 roots of this plant are often large and woody, sometimes a centimeter or more 

 in diameter, but usually smaller. They have a lateral spread of 5 to 8 feet, 

 but seldom penetrate the soil to a greater depth than 3 feet (plate 30, a). 

 From the base of the clump 6 to 12 of these roots arise. They run out laterally 

 in all directions, tapering gradually and branching freely and often dichoto- 

 mously, the ultimate branches being very minute and forming a great network 

 of absorbing brushes. From the main roots and their branches, as well as from 

 the rhizomes, great clusters of exceedingly well-branched laterals (from a few 

 centimeters to several inches in length) lay hold upon the moist soil of the 

 forest floor. In fact, the majority of the roots are confined to the surface 8 

 inches, while only one or two branches were found to reach the maximum depth 

 of 32 inches. 



Ribes lacustre. — ^This plant is characteristic of rather dense moist woodland. 

 Four specimens, 6 or 7 years old and 1.5 to 2 feet high, were examined. They 

 spread through distances of 1 to 2 feet or more by means of rhizomes or 

 prostrate stems. From the base of the clump a tap-root 10 to 15 mm. in 

 diameter arises. Instead of descending vertically, this almost invariably 

 runs off in the surface soil, dividing rapidly into many major branches. While 

 many of these are only 2 to 4 mm. in diameter, they taper so slowly that at a 

 horizontal distance of 3 to 4 feet from the plant they may still be 1 to 2 mm. 

 wide. These long, tough surface laterals pursue their winding way through a 

 length of 6 to 8 feet, frequently reaching distances of from 5 to 7 feet from the 

 plant. They are usually unbranched or only poorly branched, save for 

 isolated brushes of small laterals, until within 12 to 18 inches from their tip. 

 Here they divide up into long, slender laterals all well-branched near their 

 extremities, but not at all to the same degree as Opulaster. While many of 

 these branches end in moist duff, others penetrate downward to a depth of 

 8 to 12 inches. The major portion of the root system is confined to the surface 

 soil, but a few branches were found at a depth of 2 to over 3 feet (plate 28, b). 



Rosa acicularis. — The rose frequently occurs in the spruce-fir forest, where 

 it is a relict of earher stages in the succession. While under the lower light 

 intensity of the forest it is merely a low shrub, outside the forest it frequently 

 forms dense chaparral several feet in height. The plants are connected by an 

 extensive system of rhizomes which lie at a depth of 2 to 10 inches and vary 

 in diameter from 2 to 6 mm. These rhizomes run in all directions, branching 

 freely and at irregular intervals, giving rise to the stems which seldom reach a 

 height in the forest of more than 1.5 to 2.5 feet. The root system originating 

 from these rhizomes consists of both long and short roots. The shorter ones 

 vary in length from 1 to 12 inches. Almost from their point of origin they are 

 profusely branched and rebranched so as to form a brush-like mat. These 

 groups of thickly branched roots penetrate the surface soil in all directions, 

 forming a very efficient absorbing system. The longer roots vary in diameter 

 from 1 to 4 mm. at their point of origin and penetrate the soil downward in a 

 wandering course to a maximum depth of 2 to 5 feet. Throughout their course, 

 these longer roots are fairly well supplied with both short and long branches, 

 the shorter ones varying in length from 0.5 to 3 inches. The longer ones, 

 which are almost threadlike in appearance, may wander off in all directions, 

 even obliquely upward to a distance often of 2 feet or more. These branches 



