1917] MARKLE—ROOT SYSTEMS 185 
Rumex is common in the arroyos on the mesa; Cucurbita foetidissima 
occurs most abundantly along the banks of irrigation ditches in the 
valley; Berlandiera lyrata is confined almost entirely to the sides 
of arroyo beds. Thus it appears that the plants having this 
“adaptation” to an arid environment are in less need of it than 
most of the plants of the region. 
Fics. 6, 7.—Fig. 6, Sisymbrium canescens; fig. 7, Linum rigidum 
Astragalus diphysus and A. mollissimus——These are common 
€vergreen plants of the mesa. The root systems are similar and 
are characterized by prominent tap roots with a few large and 
several small laterals, which are generally deeply placed. The root 
tubercles are small and not numerous. A ae of A. mollissimus a 
is shown in fig. 10. eS 
Solanum eleagnifolium. This plant is very characteristic i ae 
- sandy situations and the oS ee sides of arroyos. te 
