ROOT-SYSTEMS OF PERENNIALS. 53 



composed of two laterals which left the main root just beneath the surface of 

 the soil and ran in opposite directions each for about a meter. These roots 

 were little branched and lay within 5 cm. of the surface. In addition to the 

 difference in the position of the two portions of the root-system there was a 

 further diiference in size : the deeper part being uniformly of greater diam- 

 eter than the more shallow horizontal portion. 



The older plant whose roots were examined was situated about 10 meters 

 south of the one just described. It was i meter high and bore several 

 branches, and although mature was somewhat under the average size for 

 the species. The habit of the plant is shown in plate 10. 



In the immediate neighborhood of the cactus, or growing within the reach 

 of its roots, were numerous perennials, Echinocacius wislizeni, Mcnodora 

 scabra, Jatiopha cardiophylla, Cassia bauhinoides, Acacia constricta, and Par- 

 kinsoniamicrophylla. There also were several species of annuals. The posi- 

 tion of specimens of Mcnodora and the census of the species within the 

 T;emco/or area are as follows : (i) 50 cm. northeast; (2) 1.4 meters north; 

 (3) 2 meters north; (4) 2.2 meters southwest; (5) 2.6 meters west; (6) 50 

 cm. south; (7) 60 cm. southwest; (8) 1.5 meters west; (9) 1.6 meters east; 

 (10) 2.1 meters east; (11) 1.2 meters southeast. Of these plants, only one 

 was placed so that the roots of the cactus did not go near it. The situation 

 of Jatropha and Echinocacius are indicated in plate 12. Of other perennials 

 growing in the area, two specimens of Cassia were 2.8 meters southeast 

 and 2.2 meters south respectively, one specimen of Acacia was 2.7 meters 

 northwest, and one Parkinsonia was 2.2 meters southeast. Among the 

 herbaceous iorms Astragalus nuttallianus , Daucus pusillus, Brodicea capitata, 

 Harpagonclla pabncri, and Hilaria sp., all of which except Astragalus and 

 Daucus were in flower at the time the roots of the cactus were examined. 

 No record was to be had of the number or kind of the summer annuals which 

 belonged to the area. In addition to the perennials and annuals, both of 

 summer and of winter, which were growing within reach of the cactus 

 roots, the roots of a neighboring specimen of Opuntia discata invaded the 

 area. Thus within a space of little more than 20 square meters there were 

 16 perennials belonging to 6 genera, and numerous herbaceous forms, of 

 which those appearing in winter belonged to 5 genera. This area was the 

 richest in variety as well as in number of plants, both perennials and 

 annuals, of any observed during the course of this investigation. 



The root-system of the older cactus was an extensive one, the leading 

 characters of which are shown in plates 10 and 1 1 and require little further 

 description. The root-system is composed of a widely extending horizontal 

 portion and a rather deeply penetrating portion. The former system was 

 not seen to attain a depth greater than 5 cm., but the latter reached as 

 deep as 25 cm. The horizontal roots of the first order are slender except 

 at the bases, which, as the plates show, are rather heavy. The laterals 

 branch but little except where they run imderneath stones, where, as in 



