78 



MISCELLANEOUS PUBLICATION 1271, U.S. DEPARTMENT OF AGRICULTURE 



and introgressive hybridization between ecotypes. 

 Wherever species of Cercocarpus occur together 

 or have been together, the putative hybrids are 

 found. Noteworthy intermediates are seen in 

 leaf size and structure of the shrubs. This has 

 been particularly noted in the hybridization of 

 true mountain mahogany (Cercocarpus montanus 

 Raf.), with curlleaf mahogany and littleleaf ma- 

 hogany (C. ledifolius Nutt. var intricatus [S. 

 Wats.] M. E. Jones). The hybrid, with fire tol- 

 erance transmitted from true mountain mahog- 

 any, occurs on fire scars from which curlleaf has 

 been completely lost, 



Big sagebrush subspecies with many ecotypes 

 and biotypes present tremendously impressive 

 variation. Rather than eliminate it, we need to 

 select among ecotypes of this shrub for palat- 

 ability. The differences in palatability are likely 

 related to the chemistry and amount of essential 

 oils in the various ecotypes. A simple two-dimen- 

 sional phenolic extraction on chromatography 

 paper proved useful for quickly segregating pal- 

 atable from unpalatable ecotypes (23). While 

 there is little likelihood that phenols making the 

 patterns and colored spots on the paper are re- 

 sponsible for the palatability or the lack of it, 

 excellent association was found between these and 

 observed palatability. We suspect the phenols are 

 indicative of the kinds and amounts of essential 

 oils that are present which do affect palatability. 

 This simple laboratory procedure was successful- 

 ly utilized to quickly predetermine palatability 

 of sagebrush ecotypes. The technique appears to 

 have usefulness for other species of shrubs. Cer- 

 tainly, it is clear that introgressive hybridization, 

 both sympatric and allopatric, has and is con- 

 tinuing to have a tremendous effect on the gene 

 flow from ecotype to ecotype and from species to 

 species where they are closely related throughout 

 the West because of the openings that exist for 

 establishment of progeny from Mother Nature's 

 experiments. 



The centers of diversification and origin of a 

 number of the shrub genera and species are in 

 the West. Consequently, there are more species 

 and ecotypes of shrubs assembled here than prob- 

 ably anywhere else in the world. For this reason 

 alone, there is a great amount of inherent varia- 

 tion in the germ plasm found nowhere else. This, 

 along with habitat openings for establishment, in- 



deed maximizes the chances for the creation of 

 new shrubs. I am impressed that this potentially 

 creative aspect is highly active. The fact that a 

 great many natural hybrids between closely re- 

 lated species have been observed gives credence to 

 this (18, 23, 2b, 33, 37, 54). Some of these have 

 become fairly well stabilized as in the reported 

 instance of desert bitterbrush (Purshia glandu- 

 losa Curran) (55). Further successful explora- 

 tory hybridization between several closely related 

 species substantiates what has been observed in 

 nature (18). 



Consequently, opportunities are abundant for 

 important advances in discovering improved 

 shrubs for a multiplicity of purposes. Not only is 

 there rich opportunity to select from a large as- 

 sortment of shrubs which nature has provided, 

 but given guidance, the chances are unexcelled 

 for improvement of shrubs through breeding. In- 

 deed, much basic background is lacking in the 

 area of morphogenesis, but the time has arrived 

 for strong impetus in this research. 



Literature Cited 



(1) Anderson, D. L., P. Hamilton, H. G. Reynolds, and 

 R. R. Humphrey. 



1953. RESEEDING DESERT GRASSLAND RANGES IN SOUTH- 

 ERN Arizona. Ariz. Agr. Expt. Sta. Bull. 249. 



(2) Anderson, E. 



1948. hybridization of the habitat. Evol. 2 : 1-9. 



(3) 



1953. introgressive hybridization. Biol. Rev. 28 : 

 280-397. 



(4) Beetle, A. A. 



1960. A STUDY OF SAGEBRUSH, THE SECTION TRIDEN- 



tatae of artemesia. Univ. Wyo. Agr. Expt. 

 Sta. Bull. 368, 83 pp. 



(5) Benson, L., and R. A. Uarrow. 



1944. A manual of southwestern desert trees and 

 shrubs. Univ. Ariz. Biol. Bull. 6, 441 pp. 



(6) Bentley, J. R. 



1967. conversion of chaparral areas to grass- 

 land : techniques used in California. U.S. 

 Dept. Agr., Agr. Handb. 328, 35 pp. 



(7) Bleak, A.«"T., N. C. Frischknecht, A. P. Plum- 



mer, and R. E. Eckert, Jr. 

 1965. problems in artificial and natural revege- 

 tation of the arid shadscale zone OF UTAH 

 and Nevada. Jour. Range Mangt. 18(2) : 

 59-65. 



(8) Buffington, Lee C, and C. H. Herbel. 



1965. VEGETATIONAL CHANGES ON A SEMIDESERT 



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