192 BOTANICAL GAZETTE [SEPTEMBER 
was 28 in. in height. The tap root was weak, being exceeded in 
diameter by several of the laterals. The laterals were numerous 
and arose just below the ground and proceeded horizontally 2 or 
3 in. below the surface, most of them beneath the bed of the arroyo. 
The ends of several of them dipped abruptly downward. This 
type of root is rare in the region. The root system of Parosela 
scoparia, which grows 
in sand, was found to 
be similar, but more 
deeply placed. 
Artemisia tridentata. 
—This plant grows 
along the sides of 
arroyos in the Chryso- 
thamnus association. 
Well developed speci- 
mens are rare, since 
the plant is freely 
eaten by grazing ani- 
mals. The specimen 
shown in fig. 19 grew 
in soil the upper 10 in. 
of which was adobe, 
overlying 12 in. of 
coarse gravel and 
Fic. 21.—Root system of Dysodia acerosum 
oped, but the laterals near the surface were extremely prominent. 
These were of two types: numerous short ones in the upper 12 in. of 
soil, and a few very long ones which arose from the upper 6 in. of the 
taproot. The latter proceeded horizontally 3—4 in. below the surface 
of the soil and reached a length of 20-40in. There was a tendency 
for the ends of these roots to turn downward, as in Parosela. 
Ephedra trifurca.—This is one of the dominant species of the 
_ Dysodia-Ephedra association. Investigation of a number of 
