72 



ROOT HABITS OF DESERT PLANTS. 



what larger one branched only twice. The roots of no cactus studied, and 

 in fact no perennial plant except the parasite Kramcria, branched less than 

 this one. 



The roots were slender, as the following representative measurements 

 will indicate. One of the superficial roots which was 3 meters in length 

 was 6 mm. in diameter 35 cm. from the base; another long lateral, 1.2 

 meters from its base, was 3 mm. in diameter; and a third root, 1.5 meters 

 from the point of origin on the main root, was 4 mm. in diameter. This 



Fir,. 12. — Root-system of Opiinlia fulgidn. In the sketch of the horizontal extension of O. fulgida, 

 A, two specimens of Riddellia cooperi (a) and one Acacia constncta (b) are shown. The 

 vertical extension of the roots of O. julgida is given in b, and of Acacia conslrKta in c. 



system was also shallow, the main lateral running southwest, at a point 35 

 cm. from the central axis, was 4 cm. deep, and at a point 1.2 meters from 

 the main plant axis it was 6 cm. beneath the surface of the ground. The 

 other laterals also were found to lie 5 to 6 cm. below the surface, although, 

 as was pointed out above, the soil at the place was relatively deep and 

 would have offered no obstacles to deeper root penetration. 



The roots of the 3 specimens of Riddellia cooperi, growing within the 

 root-area of the cactus, were also examined. They each sent a tap root 

 straight down, and in each root a few laterals were given off which ran in 

 a more or less horizontal direction as far as 10 cm. How deep the tap 

 root of Riddellia penetrated was not learned. At no place, however, did 

 the root-systems of Riddellia appear to occupy the same horizon as the 



