26 ROOT HABITS OF DESERT PLANTS. 



not in diameter. Only lo cm. of the main root was recovered, but it may 

 have been much longer than that, since, where it was broken, it was 0.5 mm. 

 in diameter. The root was 4 mm. in diameter at the crown. From the 

 main root 5 leading laterals take their origin. These are coarse and over 25 

 cm. long. The laterals of the first order bear numerous long delicate roots, 

 which in turn are branched. The ultimate roots are long and filamentous, 

 but rudiments, mere root tips, are also very numerous. 



The root-system of Amaranthus thus is characterized by two classes of 

 roots, coarse and fine, without intergradation, and b)'' the presence of rudi- 

 ments (plate 2). 



Anoda Thurberi. 



The specimen of Anoda which was studied was procured August 10; it 

 was an unbranched shoot 22 cm. in height and bore several large leaves. 

 The root-system is characterized by a prominent main root and several deli- 

 cate secondary ones. The tap root was over 18 cm. long and was forked. 

 From the tap root arise numerous laterals, mostly within 4 cm. of the 

 surface of the ground, of which the largest is over 6 cm. in length. The 

 laterals of the second order bear filamentous branches. No rudiments are 

 present. As a rule the roots arise singly, although a few of the ultimate 

 ones are in groups (plate 2). 



Aster Tanacetifolius. 



On August 26 the roots of Aster were removed from the soil. The plant 

 has a dense habit of growth and bears many leaves. The shoot was 25 cm. 

 high. The tap root is especially well developed. It is 4 mm. in diameter 

 at the crown, and over 15 cm. was recovered. The laterals form a dense 

 tuft 3 to 6 cm. beneath the surface of the ground and are uniformly slender. 

 There are no rudiments. 



A peculiarity, not observed in other species, was the place of origin of the 

 laterals of the second order. All of the laterals of the first order, which 

 W'cre in the dense tuft referred to, were short — that is, less than 3 cm. long — 

 and the tips were dead, but they all bore long and delicate branches, as 

 shown in plate 2 . The cause of this was not definitely ascertained, although 

 laterals with branches near the somewhat enlarged base were seen with 

 the tips yet living, so that the condition noted may be the usual occurrence 

 in the species. The ultimate roots of Aster are of the fourth order. 



Below the tuft of absorbing roots just described are scattered slender 

 laterals arising from the main root. The root habit, with the relation of 

 the laterals to the main root, is shown in plate 2. 



BoErhaavia sp. 



The specimens of Boerliaavia examined were from Tumamoc Hill near the 

 Laboratory building and were washed out August 10. The shoot of the 

 plant to be described, which was in bud, was 12 cm. high and bore numerous 

 large leaves. 



