AS CLEPIADACEAE 



to the very hot dry regions of the extreme southwest. It often- 

 grows in large clumps with many stems to the plant. The stems are 

 unbranched, straight and three to seven feet long. The rocky dry 

 sites in which this plant grows suggest the possibility of raising 

 it for rubber in the worst desert regions in the southwest. Its 

 value for erosion control purposes on any of our projects as they 

 exist at present is out of the question. 



Asclopias erosa i;j reported to be our best Milkweed for latex. 

 It is nowhere abundant in our region and its range is limited to the 

 hot dry sections of the extreme southwest. In the Tule Tank country 

 in western Pima County, Arizona this plant occupies the beds of sand 

 washes and has an intricate system of horizontal roots. Plants are 

 frequently five feet high. On cutting the stems a stream of juice 

 exudes. If this is rich in rubber this species should be worth 

 planting in sitpis of this kind. 



Asclopi as subulata resembles A. albicans and has about the 

 same range. It is a somewhat smaller plant. Experiments indicate- 

 that it is valuable for rubber. None of the above Asclcpias plants 

 have been grown in the nursery at Tucson. 



C ONV OLVULACEAE 



Dichondra argentea is too rare to have a common name and 

 too unusual and pretty to leave unmentioned. Where it grows it is 

 frequently abundant but it is suited only to very dry, rocky vara 

 situations. Naturally, it is confined to western Texas, southern 

 New Mexico, southern Arizona and adjacent Mexico. The leaves and 

 stems of this plant are silvery gray and the stems cling close to 

 the ground and root freely. Where it will grow it is an ideal 

 erosion control plant and should prove a novelty in rock gardens, 



POLEMON IACEAE 



The Gilia and Phloxes are abundant in the southwest, mostly 

 in tnc mountainous sections. Seme of the former are annuals. Many, 

 however, arc perennials. All of our Phloxes arc showy perennials 

 and some are fair erosion control plants whi£h nay sometime find 

 a place in our work. They resemble the cultivated phloxes and arc 

 interesting as ornamentals. 



HYDROPHYLLACEAE 



♦Eriodictyon angustif olium or Yerba Santa, is a shrub which 

 is abundant in many of the mountains of the extreme southwest from 

 southern Arizona to southern California, Utah and Nevada, at alti- 

 tudes of about 3,000 to 5,000 feet. The traveler between Superior 

 and Globe, Arizona is likely to observe the largo patches of this 

 shrub along the highway embankments. It forms dense stands, sprouting 



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