ROOT SYSTEMS OF TRUE-PRAIRIE SPECIES. 23 



younger ones are a dark tan. Some of the roots run obliquely to horizontal 

 distances of 2 feet from the base of the plant before turning downward, while 

 others run almost straight down to distances of 5 to 9 feet (fig. 5). The root 

 system throughout is rather poorly branched, the larger roots especially often 

 running distances of 6 to 8 inches without giving off branches. On the 

 other hand, the smaller roots may branch in a forked manner, and these re- 

 branch into long, slender rootlets furnished rather abundantly with hairlike 

 laterals. These rootlets, although several inches in length, are, like the root- 

 tips, only moderately rebranched. In the surface soil, however, the rootlets 

 may be well branched to the third and fourth order, while in soil crevices, and 

 in earthworm burrows especially, a great network of hairlike branches often 

 occurs. Thus Salvia exemplifies the deeply penetrating, widely spreading, 

 but rather coarse root system characteristic of so many prairie plants. 



Melilotus alba. — White sweet clover is a biennial ruderal throughout much 

 of the grassland formation where it has escaped from cultivation. It is an 

 excellent forage crop for semiarid regions, withstanding drought better than 

 alfalfa and often thriving where the latter crop fails. This species was ex- 

 amined on rather low-lying level land adjoining a sandy ridge near Central 

 City. The old bluegrass sod had been covered to a depth of 1.2 feet by wind- 

 blown sand from the adjacent hills. The sweet clover was planted to prevent 

 further local soil-shifting (p. 64). The roots were examined early in July, 

 1919, when the plants were just 12 months old. At this time they were 3 

 feet high, but formed rather a poor stand. The plant described had 15 stems 

 arising from the crown of the fleshy tap-root. Below the drifted sand was a 

 layer of 1 foot of black sandy loam, underlaid by 2.8 feet of fairly pure sand, 

 while at 5 feet in depth a very hard, black clay-loam was encountered, above 

 which the water oozed into the trench. The largest plant examined (plate 

 18, b) had a tap-root 1.5 inches in diameter. It tapered off gradually and at a 

 depth of 1.7 feet was only a centimeter thick. Although no major branches 

 were given off in the surface layer of sand, 5 large laterals, 5 to 8 mm. in diame- 

 ter, came off at a depth of 1.3 to 2 feet. The tap-root pursued a nearly verti- 

 cally downward course until it reached the hard layer of soil, when it turned 

 abruptly, ran horizontally for about 7 inches, and then penetrated the hard 

 black clay for only 2 or 3 inches. The first 1.5 feet of the tap-root gave off 

 numerous small laterals only a millimeter or two in diameter. These ran off 

 horizontally to distances of 0.5 to 1.5 feet or even more, filling the surface sand 

 with a delicate network of absorbing roots. Few of the main laterals spread 

 to a greater distance than 2 feet from the downward course of the tap-root, but 

 most of them reached depths of about 5 feet. All were abundantly supplied 

 with extremely well-branched sublaterals, so that the soil was well filled with 

 roots to a depth of 5 feet. Other plants examined, though somewhat smaller, 

 agreed in branching habit with the one described, though many gave off major 

 branches in the surface stratum of sand (cf. p. 131). Thus sweet clover is 

 not only quite deeply rooted, but is also fitted to absorb at all levels in the soil. 



Helianthus rigidus. — This sunflower is a prairie species of wide distribution 

 and forms extensive autumnal societies which are conspicuous both because 

 of the height and abundance of the plants. Like so many other prairie species, 

 it propagates by means of rhizomes. From the base of the plant there often 

 arise a number of these, with diameters of 2 to 4 mm., which run off in soil 

 usually not more than 6 or 8 inches deep and often at a depth of only 3 or 4 

 inches. In length they vary from 0.3 to 1.5 feet. In the main they are rather 

 destitute of roots. The rhizomes are often enlarged throughout the last 6 



