ECADS. 



119 



filling the soil to a distance of 18 to 24 inches on either side of the plant. 

 Such marked differences in root habit are probably accompanied by marked 

 changes in the aerial parts. This is a rich field for future investigation. 



Euphorbia montana. — This spurge is rather widely distributed throughout 

 the plains and mountains and is often locally abundant. Those examined 

 on the plains had a strongly marked tap-root, which started with a diameter of 

 6 mm. and pursued a tortuous and zigzag course downward to a depth of 

 7.5 feet, where it ended in pearly white, hairlike branches (fig. 57). Within the 

 first foot there were 4 short branches from 4 to 8 inches long, which were 

 themselves shghtly branched. The larger branches from this point downward 

 were very sparse, there being only one of note, which came off at a depth of 

 about 20 inches and pursued an obliquely downward course for a distance of 

 about 2.5 feet. Along the whole course of the root below the first 21 inches, 

 very fine, pearly-white, hairlike branches were found in abundance. Par- 

 ticularly was this true from 21 to 55 inches deep. In this region a large soil 

 fissure occurred, and these pearly-white branches, oftentimes arising in pairs, 

 were matted and profusely branched, extending horizontally from the main 

 root to a distance of 10 inches in some cases. The matting of these small 

 branches in the fissure was probably due to the excess of water which came 

 down from the surface. Below this fissure these branches continued, but 

 much fewer in number, to a depth of 60 inches, where a very moist, easily 

 penetrable stratum of soil was encountered. In this stratum the small 

 branches again occurred in great numbers, being sometimes 6 to 8 inches long 

 and as many as 25 per linear foot. Here, too, they often occurred in pairs. 

 The root is light brown in color. It has a fleshy cortex and a tough, fibrous 

 stele; when broken a very small amount of latex exuded. 



Compared with this root type, that of the half-gravel-slide, with its shal- 

 lower but more widely spreading and much more profusely branched roots, 

 stands out in marked contrast. It shows a profoimd series of modifications in 

 adapting itself to this very different habitat. This is evident from a com- 

 parison of figures 57 and 58, notwithstanding the fact that the half-gravel- 

 slide plant here illustrated was exceptionally deep-rooted, and from the follow- 

 ing description, which is typical of one of several other half-gravel-slide 

 plants examined. 



This was a large plant, with a tap an inch in diameter, which divided at a 

 depth of 1 inch into two nearly equal parts. The one ran up the slope in a 

 horizontal position and at a depth of only 4 to 10 inches. It soon broke up 

 into many smaller branches, which diverged in all but a downward direction 

 and extended to distances of 3 to 4 feet, and mostly only a few inches below 

 the soil surface. The second descended vertically, but gave off 2 branches 5 

 and 8 mm. in diameter, respectively, at a depth of 2 and 3 inches, while the 

 tap was now only 5 mm. in diameter. The largest of these branches ran off 

 at a depth of only 8 inches to a lateral distance of 5 feet. At 16 inches from 

 the base of the plant it broke up into numerous equal-sized branches which 

 rebranched profusely. None of these reached a depth greater than 14 inches, 

 while many of the obHquely upward running branches filled the soil to near 

 the surface with great masses of finely branched rootlets. The tap tapered 

 very gradually and after branching considerably, mostly with vertically 

 descending or oblique or even horizontal branches, reached a depth of 58 

 inches. The spread of the deeper branches on either side of the tap was only 

 about 12 inches. Tiny, fragile, glistening-white mats of branches form a 

 network of rootlets 2 to 8 inches long, surrounding all but the larger parts of 

 the older laterals. Four plants were examined. 



