Oe Se te om, 
1917] MARKLE—ROOT SYSTEMS 193 
specimens showed a considerable variation in the root system, 
which in general has a good development of both tap and lateral 
roots. The plant shown in fig. 20 grew in adobe soil about 2 ft. 
above the bottom of an arroyo and had prominent laterals and a 
stout but rapidly tapering tap root. Below the part shown in the 
photograph, two large laterals were given off, below which the 
tap root was insig- 
nificant. Another 
specimen growing 
in adobe soil to ft. 
above the bottom of 
an arroyo and ex- 
posed by erosion 
showed a relatively 
much greater de- 
tap root. Several 
laterals, the largest 
alf an inch in dia- 
meter, were given off 
in the upper 2 ft. of 
soil. Three small 
laterals occurred 
3 ft. below the sur- 
face. The tap root 
proceeded somewhat 
tortuously down- : a ' 
ward to a depth of Fic. 22.—Root system of Chrysothamnus Bigelovit 
at least 11 ft., a little 
below the level of the arroyo bed, where a large lateral arose. 
Below this the tap root had a diameter of 5 mm. and was not 
followed farther. A third specimen grew ona hill and was exposed 
by the removal of gravel. The plant grew in a soil composed of 
boulders up to 8 in. in diameter, the interstices of which were a : 
filled with sand. The root system was essentially similar to ie 
second specimen described. The cause of the variation in the = i 
appa ney is not t the c character of 
