The root-system of _Acanthyllis_ offered some points of interest and a short study of it was made in the field. All of the specimens whose roots were examined were growing in the habitat above referred to and within a meter of one another. The leading results of the observation are as follows: The largest specimen studied possessed a tap-root 3 cm. in diameter at the crown. Growing rapidly smaller as it ran downward, the root gave off four laterals, of which a portion dipped at an acute angle to a depth of 20 to 30 cm., sending off branches by the way. One of the largest of the laterals was traced 75 cm. and where left was 2 cm. beneath the surface. The branches, at least of the main laterals, that is, the roots of the tertiary order, for the most of their course ran thus near the surface of the ground. One of the leading laterals was followed to the base of a neighboring specimen of quedad, where it lay close to the crown of the main root. The depth of the penetration of the tap-root of this specimen was not learned. The tap-root of a neighboring specimen ran directly downward 20 cm.; then, turning sharply, it extended in a horizontal direction for a distance of 70 cm. As the large laterals were wholly lacking on this plant, the tap-root was the entire system—surely an anomalous condition. On a third plant the tap-root penetrated the ground about 4 cm. only, after which it turned and ran the rest of its course within 4 cm. of the surface. The more superficial of the roots of a fourth specimen were found to extend to the base of the last plant mentioned. Thus it was found that the root-system of _Acanthyllis_, as growing naturally, extends both widely and deeply for a considerable distance, and that it is flexible to a degree; in short, is generalized[8] and closely resembles that of certain species of the Tucson region, particularly _Covillea tridentata_, which grows under similar conditions. The root-systems of three or four other species were also examined. Of these _Zollikoferia spinosa_ and _Artemisia campestris_ were growing in a little hollow in the plain close by the habitat of _Acanthyllis_. _Zollikoferia_ has a very close habit of growth with dichotomous branching (compare figs. 5 and 7). When dry the branches are slender and of a woody hardness. The root-system of this species is characterized by a pronounced tap-root and by the absence of large laterals, at least near the surface. The leading feature of the root-system is, in short, its tap-root. A root-system of a similar type was found in _Artemisia herba-alba_.