THE GRAVEL-SLIDE COMMUNITY. 



87 



Mentzelia multiflora. — Size, duration, and abundance combine to make 

 this species a dominant on many gravel-slides. The plants are usually about 

 10 to 14 inches high when in full bloom. The roots start with a tap 12 mm. or 

 less in diameter, which, after penetrating to a depth of 2 to 5 inches, sends off 

 strong laterals as large as 3 or 4 nma. in diameter. These are distinctly shallow, 

 run almost parallel with the surface, and are repeatedly branched, the 

 fine rootlets ending in hairhke extremities. Although they seldom run more 

 than 18 inches from the base of the tap, they are frequently much longer 

 because of their curved and twisted course. The tap-root takes an almost 

 vertically downward course, except where it follows for a time the crevices in 

 the rocky soil, and penetrates to a maximum depth of about 22 inches. 

 Although the tap is not so profusely branched as are the shallower laterals, the 

 branches of both are very similar. The smaller branches of both the laterals 

 and the tap are profusely covered with a fine growth of root-hairs. Although 

 this plant, when compared with most others, has an exceedingly well-developed 

 absorbing system, it does not compare favorably with the wonderfully exten- 

 sive and excellently developed root system of Aletes. However, both are well 

 adapted to get the water falling during the frequent mountain showers and 

 thrive under conditions where most plants could not grow. The roots are 

 almost white in color and very spongy in texture. 



Eriogonum flavum. — This plant is a subdominant in the gravel-slide com- 

 munity, its masses of yellow flowers making it very conspicuous in the 

 autumnal aspect. The specimen had a strong woody tap-root 2 cm. in 

 diameter which tapered within a length of 6 inches to only 3 mm. in diameter. 

 Here it gave off 2 laterals each 2 mm. in width. These ran off laterally for 

 about 2 feet at a depth of 3 to 7 inches. An enormous number of smaller 

 profusely branched laterals arose, forming a dense absorbing network about 



Fig. 36. — Eriogonum flavum. 



