- 6 - 

 species of outstanding Talue as a rubber plant was discovered in this survey. 

 Genera containing species with a benzene extract (rubber content) in excess 

 of one percent of dry weight were: Apocynum, Asclepias^ Eueomia , Euonymu8» 

 Euphorbia « Lonicera« Parthenium, and Solidago , Tn comparison of 3-hour and 

 20-hour extraction periods with benzene there was little difference in the 

 amount of the extract obtained Aram plants of Apocynum , Aselepias, Chrysothamnus , 

 Euonymus. Lonicera, or Solidago ; but plants of the genus Lactuca yielded much 

 higher extracts (1.9-2.9^) from the 20-hour period than from the 3-hour period 

 (0.6-O.d^). 



Genera containing species with an acetone extract (resin content) in ex- 

 cess of 20^ of dry weight included the following: Acer. Apocynim. Arctostaphy- 

 los. Asclepias. Baptisia. Bet\ila. Campanula, Chrysothamnus . Comptonia. Cotinus. 

 Daucus , Euonymus. Eupatorium. Euphorbia. Grindelia. Lonieera. Rhus. Solidago . 

 and TragopogCTi . 



BEFEEENCES 



1. Buehrer, T.F., and L. Benson. Rubber content of native plants of the south- 



western desert. Tech. Bull, l&iiv. Ariz, agric. Exp. Sta. lOd: 1-33* 



1945. 



2. Hall, H.M., and T.H. Goodspeed. A rubber plant survey of western North 



America. Ohiv. Calif. Publ. Bot. 7: 159-278. 1919. 



3. Polhamus, L.6. Rubber content of various species of goldenrod. J. agric. 



Res. 47: 149-152. 1933. 



4. SpencOf D., and M.L. Caldwell. Detennination of rubber in rubber-bearing 



plants. Industr. Ehgng Chem. (Anal.) 5: 371-5. 1933* 



5. Willets, CO., C.L. Ogg, W.L. Porter, and M.L. Swain. Determination of 



rubber in fleshy and woody tissue plants. J. Ass. off. agric. Chem. 

 29: 370-387. 1946. 



