ROOT-SYSTEMS OF PERENNIALS. 



59 



Fig. 6. — Root-systems of Covillea tridenlala, from various locations on the domain of the 



Desert Laboratory. . . , r , 



a and h. Horizontal extensions of root-system of one plant, separated tor sake ot clearness. 



Dotted lines indicate the intruding roots of neighboring Covilleas encountered on the 



same level, or nearly so. as the roots of the plant studied, 

 c, Vertical extension of bajada-grown plant. , , . , „. „, , 



d and r. Vertical extensions of root-systems of two plants from the flood-plam of Uest \V ash. 



Hntire length of laterals in c is not shown. 



About ID large and numerous small laterals were given off from the 

 main root within 15 cm. of the surface of the ground. These roots were 

 from 5 mm. to i.i cm. in diameter at the base, and the longest extended 

 as far as 4 meters from the central root axis. This, the longest lateral, 

 branched from the main root 3 cm. from the surface, and lay 21, 39, 31, 

 and 28 cm. from the surface of the ground at various distances from its 

 base. The position of this root with relation to the surface is fairly illus- 

 trative of all of the rest. The mutual relations of the principal roots, 



