ROOT-SYSTEMS OF PERENNIAI.S. 



65 



parvifolia, Opuntia discata, Opuntia versicolor, other species of Opuntia, and 

 Parkinsonia microphylla. 



The soil of the habitat is much hke that of the portion of the bajada at 

 the northern base of Tumamoc Hill, where Covillea was studied, adobe clay 

 constituting the upper soil to about 20 cm. depth, under which is rotten 

 caliche, the latter resting on hard caliche. The situation is probably the 

 most severely arid of any habitat studied. 



Fig. 9. — Vertical extension of the root-system of Franseria deltoidca from 

 different habitats, a, root-system of a bajada-grown plant. Upper 

 surface of caliche hardpan indicated by dotted line. 6, root-system of 

 a plant from the flood-plain by West Wash to show depth to which 

 tap root penetrated, 1.8 m. 



Two specimens of Franseria from the bajada habitat and one from the 

 flood-plain of West Wash were examined. Therefore, as regards soil con- 

 ditions and water relations, the two habitats present the greatest contrast 

 to be found on the domain. 



