64 ROOT HABITS OF DESERT PLANTS. 



' A character of the smaller roots of the plant was the bearing of groups of 

 filamentous, adventitious rootlets about i cm. in length. At the time the 

 study was made, January, these rootlets were dead. 



The only roots of neighboring plants which intruded on the root-area of 

 Fouquieria were two of Parkinsonia micro phylla, which lay 3 and 15 cm. 

 from the surface of the ground. 



The larger specimen of Fouquieria examined was 1.75 meters high and 

 bore numerous long branches. In February, when the study was made, the 

 plant was without leaves. 



The following were the main characters of the root-system of the larger 

 plant. A tap root penetrated the ground until it met a mass of caliche 

 which lay immediately below the base of the plant. The depth attained by 

 the root was about 15 cm. Five laterals arose immediately below the sur- 

 face of the ground ; they were 5 cm., more or less, in diameter, at the base. 

 It is a characteristic of Fouquieria that the roots, although relatively heavy 

 at the base, taper rapidly; for example, one 5 cm. in diameter at its base 

 had a diameter of i.i cm. about 50 cm. away. After the diameter of i.o cm. 

 is reached, the root maintains this very closely for a considerable distance. 



The depth usually attained by the laterals may be illustrated by a few 

 examples. Taking a typical root, we find that while it leaves the tap root 

 immediately beneath the surface of the ground, at a distance of 40 cm. it 

 is 25 cm. deep ; at 50 cm. it is 16 cm. deep ; at a distance of i meter it is 23 

 cm. beneath the surface; and at a point 1.75 meters from the main axis, 

 where it is 2 mm. in diameter, the root is 21 cm. deep. A branch of this 

 root was traced downward to a depth of 37.5 cm., but at that point it was 

 no longer living. 



Groups of filamentous roots were not seen in the larger specimen. There 

 were several specimens of Covillea in the area included within the scope of 

 the roots of Fouquieria. One was about 25 cm. distant and its roots occu- 

 pied much the same area as those of the Fouquieria, but they were deeper 

 and, although the roots of Fouquieria were exposed with great care, only 

 four instances were noted where roots of the neighboring Covilleas were 

 found in the same horizon as those of the plant examined. Competition 

 between the two species of shrubs, therefore, is probably not very active. 



Franseria Deltoidea. 



Although perhaps as widely distributed locally as Covillea, the character- 

 istic habitat of Franseria deltoidea on the domain of the Desert Laboratory 

 is the bajada, just to the west of West Wash. In this habitat the popula- 

 tion of Franseria for any given area is greater than that of any other shrub 

 in its characteristic habitat in this vicinity. In fact, the species at the 

 place in question fairly completely conceals the ground. 



In the neighborhood of the Franseria examined, the following woody 

 plants also occurred: Covillea tridentata, Krameria canescens, Krameria 



