2")2 JJniversihi of CdJifoniia f'lihlicdfiotis in Jiotdtn/ |\in.. 7 



Ivubbcr Plant {II ijiik no.ijjs j{urihiiit(Ui i(tilis) lias hccii iiiisiu^eessfully 

 tried and the (Juayidc a shrub native to oui- soutlurn boidcrs and to 

 Mexico, is now iukUt ti'ial in Arizona. Since none of these rubber 

 ])lants luis as yet been ajjrieulturally established in the Tnited States 

 it would seem worth while to yive attention also to (Uiri/sodKim iiu.s as 

 a possible plant to t)e brou<:ht under cultivation t'oi- its luliher. 



If a further incentive is needed for the study of rubber plants 

 suitable to our conditions it may be found in the extent of uinised and 

 apparently unusable lands that are still to be found in our western 

 states. The inti-oduction of new af?ricultui'al industries for the i)roper 

 utilization of these practically idle lands is one of the most important 

 problems that now confront the people of the arid West. While we 

 hesitate to predict that they will ever l)e used foi- the pi'o(hiction of 

 rubber, yet that this is within the realm of i)Ossibility is evidenced by 

 the planting of a considerable acreage to Guayule in southern Aiizona 

 in 1918 by one of the leading rubber companies. 



Guayule is a small ^Mexican shrub belonging to the same botanical 

 family as th(> Kabbit-brush, although not vei-y closely related to it. 

 The similarity between the two is such that a consideration of the 

 Guavule situation mav furnish some evidence as to the possible worth 

 of Chrysothamnus. The wild Guayule yields a "rubber" which 

 had been imported into the United States in considerable (luantity-- 

 hefore the political troubles in Mexico interfered with the industry. 

 The supply of wild shrub was constantly on the wane, which \vd to 

 extensive experiments in propagation, selection, breeding, and culti- 

 vation. The wild plants carry an average of 10 per cent of "(hiayule 

 gum," as it is called, but when they were brought under cultivation 

 it was found that some plants yielded only 2 or 3 per cent, and in some 

 cases less than 1 per cent, of pure rubber. The application of .scien- 

 tific methods of breeding and selection, together with the control of 

 environmental conditions of growth have now brought the yield to as 

 high as twenty-seven per cent in a f(>w plants. We understand that 

 these high percentage strains are not suitable for iield gi-owing Imt 

 that those selected for j)lanting on a large scale yiehl about tifteen to 

 seventeen per cent of rubber in their fifth or sixth yeai". 



These experiments with Guayule extended ovei- a ten-year ])ei-iod 

 and ai-e said to have cost one company alone in the neighborhood of 

 $r)0(),0()0. Their promise, however, may be inferred from the present 

 intention of the ccmipany to undertake planting in Arizona on a large 



;!2 (19,000,000 poniuls in 1911.) 



