288 JOHN ERNST WEAVER 



anchor the plant in place and lay hold upon the moisture of the 

 superficial soil layers. It is a notable fact that the Eriogonums 

 (including E. compositum and E. niveum) blossom and appear 

 to thrive when most other plants of the rim-rock have long since 

 dried out. This is explained in part by their extensive root- 

 systems, of which the one shown in the figure will be described. 

 A few others were excavated as checks. 



The strong, woody, tap root 1 inch in diameter broke up at a 

 depth of 6 inches into seven nearly equal laterals; only about 

 one-fourth of the old tap root is shown in the figure. One of 

 these laterals extended a distance of 13 feet and 6 inches as 

 measured in a direct line from the plant, but had an actual 

 length of 14 feet and 3.6 inches. It tapered off gradually, 

 throwing off both large and small laterals which branched to the 

 fifth order. Upon leaving the main tap it ran along in very 

 shallow soil for 7 feet and 6 inches before turning down in the 

 rock crevices, where it followed a very devious route dipping 

 up and down more than a foot, and branching profusely to the 

 tip. 



Some examinations were also made of the roots of Rosa nut- 

 kana, and Symphoricarpos racemosus, both very common in 

 nearly all prairie situations. They were found extending to 

 depths of from 6 to over 8 feet. Iris missouriensis roots pene- 

 trated the soils of dry hillsides to 3 feet and 10 inches, and Ber- 

 beris repens to a depth of over 10 feet. The orange-yellow 

 roots of the latter, arising from the great system of horizontal 

 stems on the rim-rock (where it often forms societies), resemble 

 Eriogonum heracleoides in their abundant laterals and in the 

 devious route they pursue in following the basaltic crevices. 



Likewise, two species of Lomatium,L. grayi andL. inacrocarpum, 

 both abundant on thin soils, were examined. The long, fleshy, 

 poorly branched taps are usually flattened, folded, and twisted 

 as they crowd into the narrow crevices of the rock to depths of 

 3 to 5 feet or more. On the other hand, Polygonum majus, 

 growing with Poa on thin stony soil, has a shallow but well de- 

 veloped root-system. The tap, seldom over 6.5 inches long 

 (and usually less), sends off laterals profusely. In spite of the 



