Mat 10, 1918 



SCIENCE 



453 



the border of the continental United States 

 could be utilized. It mifrht be noted here that 

 the quality of this new rubber is, according to 

 rubber experts, somewhat better than the best 

 grades of guayule. but not as good as Para. 



The choice of Chrysothamnxis and related 

 genera as the plants first to be investigated 

 was the result of a preliminary examination 

 made in 1904. In September of that year the 

 late Judge A. V. Davidson, of Independence, 

 Inyo County, California, sent some twigs to 

 the Department of Botany for identification, 

 with the information that the Indians prepared 

 from the plant a sort of " gum " which they 

 chewed. The plant was a species of Chryso- 

 tJiamnus of the graveolens group. Further 

 samples were submitted at our request, and in 

 October, 1905, a preliminary chemical exami- 

 nation of them was made by Professor G. E. 

 Colby, of the California Experiment Station. 

 This examination indicated the presence of 

 rubber, but not in sufficient amount to warrant 

 further investigation. A report to this effect 

 was made public in the press and as a result 

 some further examinations were made by at 

 least one commercial rubber company. The 

 matter was soon dropped, however. It is prob- 

 able that the plants used in this commercial 

 examination were of an entirely different spe- 

 cies from those now being examined. 



During the past year some 200 different 

 plants have been studied in detail, both in the 

 field and in the laboratory. As a result it 

 can now be definitely stated that many species 

 of Cltrysothamnus (formerly known as Bige- 

 lovia and commonly called rabbit-brush, or 

 golden-bush) carry rubber in at least small 

 quantities and that it occurs also in three 

 species of Ericameria and in one species of 

 Stenotus. 



One species of Ericameria carries 9.5 to 10 

 per cent, of pure rubber, in addition to about 

 9 per cent, of acetone-extraetable resins, etc. 

 Although this plant possesses agricultural pos- 

 sibilities, it is too small and occurs too spar- 

 ingly to be considered as a source of wild 

 rubber. In six species of Chrysothamnus the 

 older parts carry from 3 to 5 per cent, of 

 rubber. This percentage is for dry rubber 



and does not include the resins or other ace- 

 tone-soluble impurities. The term "species" 

 is here used in a narrow sense. The six spe- 

 cies referred to are all allies of C. nauseosus, 

 C. graveolens, or C teretifoUus. Further tax- 

 ononiic studies will be necessary before final 

 determinations can be made, since some of 

 the forms do not correspond to any of the de- 

 scribed species. 



Tlie most important of these species is a 

 large shrub, the rubber-producing portions of 

 which commonly weigh from two to ten 

 pomids, with a maximum observed weight of 

 about sixty pounds. It forms nearly pure 

 stands of considerable extent in some parts of 

 the Great Basin Area. Histological examina- 

 tions indicate that the rubber content is fairly 

 uniform throughout its distribution. Much 

 care must, however, be exercised to avoid con- 

 fusion with closely similar forms, some of 

 which exhibit marked fluctuation in their rub- 

 ber content, while others uniformly carry not 

 even a trace of this substance. Professor P. 

 L. Hibbard, of the California Experiment 

 Station, who has made the chemical analyses, 

 reports for the most important form as follows : 



Acetone Benzol 



Extract, Extract. 



Per Cent. Per Cent, 



Plant 1, base of stem 3.74 5.06 



Plajit 2, base of stem 3.90 4.40 



Assorted plants, trunk and root 



bark 3.90 7.80 



These figures are for fairly dry shrub. If 

 based upon perfectly dry shrub the percentages 

 would be somewhat higher. 



Field e.xperiments have been instituted to 

 determine the possibility of inducing a greater 

 growth of the rubber-bearing tissues and also 

 to determine whether or not it is feasible to 

 harvest the rubber without killing the plants. 

 Some attention is also being paid to the pos- 

 sibility of bringing the plants under culture 

 for commercial purposes. 



It is now proposed greatly to extend the 

 scope of the investigation and to include many 

 more species. In addition to locating the 

 principal supply of the more promising species 

 and its extent, we hope to study more inten- 



