ECADS. 81 



may either end abruptly or gradually taper away again. The enlarged portion 

 is often several inches long. These enlargements most often occur on the 

 larger roots, and especially on those which are extending rapidly into new 

 territory. Usually they are quite devoid of branches. They are apparently 

 developed under normal conditions and seem to be due almost entirely to 

 an increase in the growth of the cortical tissues. Waterman (1919) has ob- 

 served the same phenomenon in Juncus balticus and other dune species about 

 Lake Michigan and suggests the name "pioneer" or invading root-tip. 



Further examination of this species was made at Yuma, Colorado, where in 

 a valley of sandy loam it was dominant in a turf of short-grasses (plate 7, b). 

 Here again the surface spread of the laterals was found to be very great. 

 Large masses of roots ran out to distances of 1.3 to 1.7 feet or more in the 

 surface 0.4 foot of soil. However, these widely spreading roots, which came 

 off at all angles from the vertical, were supplemented by many more which 

 penetrated vertically downward. These roots, like the soil in which they 

 were growing, were intermediate in type between those described in nearly 

 pure sand and those of clay-loam. 



A final examination of this species was made on a hillside at Seneca, Ne- 

 braska, where the bunches were exceedingly well developed and where it was 

 a dominant species (plate 8, a). The flowering stalks reached a height of 2.3 

 feet, and many of the bunches were 1.5 to 2 feet in diameter. They were 

 composed of scores of individual stems, the old leaves and dead stems persisting 

 for a number of years. This species has in size, duration, and abundance all 

 the prerequisites of a dominant, and in fact is the bunch-grass of widest dis- 

 tribution and most controlling influence. 



From one-half to two-thirds of the exceedingly well developed root system 

 spreads laterally in the surface 1 to 1.5 feet of sand. Some roots ended at a 

 depth of only 0.4 to 0.7 foot, but at a distance of 3.3 feet from the base of the 

 clump. One root was traced to a horizontal distance of 3.8 feet from its 

 origin. It ended with a well-branched tip at a depth of only 1.5 feet. Some 

 penetrated laterally at various depths as far as 3.8 to 4.2 feet. All were well- 

 branched, some of the deeper oblique roots sending up more or less vertical 

 branches which ended near the surface. But while many of the roots ran 

 out obliquely at all angles between the vertical and horizontal and thus 

 furnished an excellent surface absorbing system, others penetrated nearly 

 straight downward; these, with the oblique roots which often turned down- 

 ward and reached a depth of several feet, provided for absorption in the deeper 

 soil. Many of these well-branched roots reached depths of 6 or 7 feet, and 

 some were found at a maximum depth of 8 feet. The working depth of most 

 of these deeper roots was about 6.7 feet. Throughout, the root branching 

 was very profound, the root-ends being unusually well supplied with branches. 



It may be seen from these data that the root system of the little bluestem 

 is always well developed but quite variable. Its extreme range in depth from 

 2.3 feet in poorly disintegrated subsoil to 8 feet in the sandhills is indeed 

 remarkable and is equaled only by its marked variation in lateral spread, 

 especially in the surface soil. In clay or silt-loam this is normally only about 

 10 or 12 inches, but as the substratum becomes sandier the lateral spread and 

 proportion of roots in the shallower soil increase, reaching the maximum in 

 the sandhills. Of all the plants examined, those at Seneca were the largest, 

 the others, although old plants, having been either grazed or annually mown. 

 This may account in part for the exceptionally great depth of the roots on the 

 steep hillside at the former station, although repeated partial burial by the 

 sand may also have been a factor. The great plasticity of the root system 

 of this species is undoubtedly a factor accounting for its wide distribution. 



