48 



THE ECOLOGICAL RELATIONS OF ROOTS. 



Fig. 11. — Gutierrezia sarothrce showing 

 wide lateral spread of roots in the 

 surface soil. 



Fig. 12. — A small part of caudex of 

 Yucca glauca, showing number and 

 extent of horizontal roots, many 

 exceeding 25 to 30 feet in length. 



