1917] MARKLE—ROOT SYSTEMS 199 
the plant owes its success as a ruderal in so many associations 
(figs. 29, 30). 
Atriplex canescens.—This evergreen shrub is common on the 
fans at the mouths of arroyos and less so along the sides of the 
smaller arroyos. A small plant 18 in. in height and growing in a 
small arroyo was selected for excavation. The upper 15 in. of the 
soil was sandy adobe, underlaid by 32 in. of coarse sand and gravel 
and 15 in. of hardpan. The plant had a strong tap root which 
forked at a depth of 32 in. One branch continued vertically 
downward and penetrated the hardpan layer. The other branch 
Ais 
mwweeeen ww +e ee we we ee ee ee 
ee cee eee te tee ede cece weet ts ee 
Cs) eae eek we ee pe 2 ee 8 oe 
Fic. 28 a, 7 Se ee, een * - 4 me ff oT. wo. 
. le j 
root penetration was evident fom the twisted character of the ) 
fonts es 32; 32, 33): os : 
(|.  dycum pallidum.—This solana eo 
— [ane Heiiho ee mie TOY oye yo 
