210 Unir< r.slhj of California ruhlicaiions in Botanij [Vou 7 



stati' hccii tlioi'onjjlily cxainincd. Tlic seven districts reported upon, 

 liowever, furnish some indieatioii of tlie total amount of rubber tlial 

 mi^lit be obtained in case of need. The estimated amount alread.N- lo- 

 cal e(l by districts is as follows: 



Pounds 



J)istik-t ] — East Central Calit'oniia and adjai-cnt >.'i'va(la 3,280,000 



District 2— Mojave Desert, California 400,000 



District 3 — Northeastern California and adjacent Ncvaila and Oregon 1.000,000 



District 4— West Central Nevada 7,(i80.000 



District 5— Northern and Central Nevada 23,700,000 



District (5— Utah 20,000,000 



District 7— Colorado 24,300,000 



80,360,000 



Taking this total of approximately 80,000, 000 ])()uii(ls as represent- 

 ing the ])robable amount of pure rubl)er present in the shrub located, 

 it is believed that this estimate could be safely increas(d by 50 

 per cent by allowing for the presence of other areas within these dis- 

 tricts, althoufih we have not been able to visit them. After this has 

 been done, we have still to account for several whole states as well as 

 several fractions of states lying outside the seven districts noted above. 

 We hesitate to venture a guess as to wliat tliese might yield but it 

 seems i)robable that the total amount in all of the western states is 

 not less than 300.000,000 pounds. 



VIII. METHODS OF DETECTING THE PRESENCE OF 

 RUBBER AND DETERMINING ITS AMOUNT 



(I. :\IICROSCOPICAL METHODS 



Microscopical examinations of Chrysothamnns and related genera 

 were at first undertaken as a short cut method of determining whether 

 or not a given sample of shrub contained rubber. In addition we liave 

 attempted, with some success, to emjiloy the microscopical method for 

 estimating the relative amounts of rubber in the different samples. At 

 the beginning of the investigations we were forced to rely ui)on this 

 method almost entirely since facilities could not be secured for nuiking 

 ourselves the many chemical analyses which luivc since been carried 

 through. Chemical analysis is, of course, the only method of making 

 both the oi'iginal determination and of obtaining an estimate of rubber 

 present which is at once thoroughly dependable and i-eally significant. 



