1917] MARKLE—ROOT SYSTEMS 187 
irregular form, without evident differentiation into tap root and 
laterals. The main root often proceeds horizontally and is little 
larger than the minor roots. The specimen shown in fig. 13 grew 
in pure gravel. 
Euphorbia sp.—This small, prostrate plant grows on the sides 
of arroyo beds. The root system has much the same general form 
Fics. 9, 10.—Fig. 9, Rumex hymenosepalus; fig. 10, Astragalus mollissimus 
as that of Sphaeralcea, but all the roots are slendex, brown, and 
fibrous. The identity of the tap root is lost a short distance below S 
the surface. The slender ultimate branches are very numerous. 
The root system is not deep, but very ee | weareeeas 2. 
limited amount of soil hei. |: vs 
__ Sphaeralcea cuspidata.—This plant is very | comr Or 
Bouteloua and pees edra associations. The plant 
