Purchased by U.S. Department of Agriculture for Official Use

Xerophytic Species Evaluated for Renewable Energy Resources 1

M. E. CARR,2 B. S. PHILLIPS,2 AND M. O. BAGBy3

Previously, the USDA Northern Regional Research Center has examined 600 plant species in 88 families for their multipurpose, energy-producing potential. About three-fourths ofthese species have been from central and southern Illinois, but only about 2% have been from arid or semiarid regions ofthe United States. For this report, 100 species collected from Arizona were evaluated, bringing the total number ofspecies evaluated at this Center to 700 in 96 families. Plant spec­ imens were analyzed for yields offractions referred to as "oil," "polyphenol," "hydrocarbon," and protein and were examinedfor botanical characteristics. Oil and hydrocarbon fractions of selected species were partially characterized. Ten species gave high yields ofoil and/or polyphenol. For example, Asclepias linaria yielded 8.7% oil (dl)', ash-free sample basis) + 11.7% polyphenol (1.9Q6 hydrocar­ bon). Rhus choriophylla yielded 7.0% oil + 20% polyphenol (0.4% hydrocarbon) and Juglans major yielded 7.0% oil + 9.4% polyphenol (0.2% hydrocarbon). Pit­ tosporum tobira gave the highest yield ofhydrocarbon (2.3%). Fourteen species contained at least 18% protein. In general, the percentages of species yielding substantial amounts of oil and/or polyphenol were considerably higher for the Arizona species than for those 600 species previously analyzed. Complete analyt­ ical data are presentedfor 38 species and are discussed in relationship to the 600 species previously reported.

In recent years, there has been much interest in developing and using more effectively plants that are able to tolerate arid and semiarid areas, particularly for industrial nonfood uses (Davis et aI., 1983). The use of new crops grown in underused land areas could supplement our need for fuels and chemicals, as well as stimulate industrial and economic growth (Buchanan and Duke, 1981; Bungay, 1982; Calvin, 1983; Princen, 1983). Currently, our Center is screening plant species in a program designed ultimately to identify plants that have potential uses as multipurpose, energy-producing crops. Previously, we have screened 600 plant species in 88 families (Carr, 1985). Most ofthese plants were collected from central and southern Illinois. This report discusses our evaluation of 100 addi­ tional species collected from Arizona, which brings our total to 700 species screened in 96 families. Plant materials were analyzed for contents of"oil," "polyphenol," "hydrocarbon" and protein. Oil and hydrocarbon fractions of selected species were partially characterized. Analytical and botanical criteria previously estab­ lished at this Center were used as an aid in selecting species for discussion. Data are compared to those of the 600 species previously analyzed.

I Received 18 June 1984; accepted 5 January 1985. 2 Northern Regional Research Center, Agricultural Research Service, USDA, Peoria, IL 61604. The mention of firm names or trade products does not imply that they are endorsed or recommended by the USDA over other firms or similar products not mentioned. 3 Northern Agricultural Energy Center, USDA, Peoria, IL 61604.

Economic Botany, 39(4), 1985, pp. 505-513 © 1985, by the New York Botanical Garden, Bronx, NY 10458 506 ECONOMIC BOTANY [VOL. 39

TABLE 1. ANALYTICAL DATA OF PLANT SPECIES WITH RATINGS OF LESS THAN 11.'

Collector Family and Herbarium Polv- Hydro- Pro- Species collection voucher Oil phenol carbon tein Rat- Common name Type of plant areab number qh tv.0 0/.0 qb ing Anacardiaceae Rhus choriophylla shrub H,SC 80366 7.0 20.0 0.4 7.0 9 Woot. and StandI. Skunkbush Asclepidaceae Asclepias linaria Cav. herbaceous H,P 80176 8.7 11.7 1.9 8.5 8 perennial Boraginaceae Cordia boissieri evergreen shrub M,P 80385 3.6 8.7 1.2 12.3 9 A. DC. or tree Anacahuita Chenopodiaceae Atriplex elegans (Moq.) herbaceous M,P 80133 2.1 4.4 0.1 20.9 10 D. Dietr. annual Four-wing saltbush Compositae Artemisia ludoviciana herbaceous H,P 80190 2.1 7.7 0.5 8.6 10 Nutt. subsp. albula perennial (Wooton) Keck White sage Baccharis glwinosa evergreen shrub M,P 80132 2.6 9.7 0.4 15.7 9 Pers. Seep willow Guardiola platyphylla herbaceous H,SC 80381 2.6 5.0 1.5 5.1 9 Gray perennial GWierrezia micro- herbaceous M,P 80375 2.2 8.9 0.5 8.5 10 cephala (DC.) Gray perennial Threadleaf snakeweed Hymenoclea monogyra shrub H,SC 80368 2.0 15.7 0.0 14.2 10 Torr. and Gray White burro bush Euphorbiaceae Jatropha cardiophylla shrub M,P 80238 2.4 3.9 0.1 14.5 10 (Torr.) Muell. Arg. Sangre-de-Cristo Garryaceae Garrya wrightii Torr. shrub H,P 80255 3.8 12.2 1.9 6.1 9 Silk-tassel bush Juglandaceae JuglallS major (Torr.) tree M,P 80221 7.0 9.4 0.2 10.4 10 A. Heller Arizona walnut Leguminosae Cassia leptocarpa herbaceous M,P 80245 4.0 4.8 0.1 15.8 10 Benth. perennial Slimpod senna Elythrina flabelliformis shrub or tree H,P 80189 3.7 8.8 0.2 15.8 10 Kearney Coral bean Robinia neomexicana shrub H,P 80392 2.4 7.6 0.0 19.9 10 Gray Mexican locust 1985] CARR ET AL.: XEROPHYTES AS ENERGY SOURCES 507

TABLE 1. CONTINUED.

Collector Family and Herbarium Poly. Hvdro- Pro- Species collection voucher Oil phenol carbon lein Rat· b 0' Common name Type of plant area number go t}o iO (}" iog Onagraceae Oenothera hookeri herbaceous M,P 80284 5.6 8.0 0.1 7.8 10 Torr. and Gray biennial Hooker's evening primrose Pittosporaceae PittosporUIIl tobira shrub or tree M,Mc 80383 4.1 5.1 2.3 8.8 8 (Thunb.) Ail. Mock orange Solanaceae SolanulIl eriantlzulIl shrub or tree M,P 80376 2.4 6.6 0.1 21.7 10 D. Don.

a Percent yields are on a dry. ash-free sample basis.

b Plant specimens ,..'ere collected by Robert \V. Hoshaw. Department of Ecology. University of Arizona. Tucson. AZ. and by Charles T. j\'lason, Jr.. Curator of Herbarium. University of Arizona. H = Hoshaw. rvl = .t-.lason. SC = Santa Cruz County..A.Z. P = Pima County, AZ. Me Maricopa County. .AZ. See Experimental.

EXPERIMENTAL Specimens were collected in 1982 from the Arizona counties of Pima, Santa Cruz, and Maricopa. Herbaceous specimens were collected as mature, whole plants, clipped at ground level. Trees and large shrubs were sampled by cutting the latest year's growth. Voucher specimens are stored at the USDA Northern Regional Research Center herbarium. About 2 lb of each plant sample was dried at ambient conditions in a sheltered area, near the collection site. The air-dried samples were ground in a Wiley mill to pass l-mm-diameter holes and then analyzed for moisture, ash and protein (% Kjeldahl nitrogen x 6.25). About 50 g of each milled sample was extracted in a Soxhlet apparatus with acetone and then hexane (48 h each solvent). Constituents from acetone extraction were par­ titioned between hexane and aqueous ethanol to obtain fractions, referred to as "oil" and "polyphenol," respectively. Constituents from hexane extraction are referred to as "hydrocarbon." Ifyield ofoil was at least 3.0% (dry, ash-free sample basis), the oil was analyzed for classes of lipid constituents by thin-layer chro­ matography and, after saponification, for yields of unsaponifiable matter (UM) and free acids (FA). Ifyield of hydrocarbon was at least 0.4%, the hydrocarbon was analyzed by infrared (IR) spectroscopy to detect the presence ofrubber, gutta, and/or waxes. Rubber and gutta were analyzed for average molecular weight by gel permeation chromatography. Details ofthe various analytical procedures have been described recently (Carr, 1985).

RESULTS AND DISCUSSION General Ofthe 100 Arizona species analyzed, yields ranged from 1.0-8.7% oil (dry, ash­ free, sample basis), 1.6-30.2% polyphenol, 0-2.3% hydrocarbon, and 3.3-32.9% protein. Twenty-three species yielded at least 3.0% oil, 9 yielded at least 4.0% oil, 508 ECONOMIC BOTANY [VOL. 39 and 3 yielded at least 7.0% oil. Polyphenol yields were at least 10% for 32 species, 15% for 15 species, and 20% for 5 species. Yields of hydrocarbon were at least 0.6% for 9 species, 0.8% for 6 species, and 2.0% for 1 species. Protein contents were at least 14, 18 and 22% for 26, 14 and 3 species, respectively. The percentages ofspecies yielding substantial quantities ofoil and/or polyphenol were greater for these Arizona species than for the 600 species previously analyzed. For example, about 5% ofthe 600 species had 4% or more oil, and about 1% had 6% or more oil. Another 5% had 15% or more polyphenol. Fewer than 1% had 20% or more polyphenol. With few exceptions yields ofhydrocarbon have been low «2%) for species collected from all of the regions investigated to date (Roth et al., 1982; Carr, 1985). Each species was assigned a numerical "crop rating," based on yields of oil, hydrocarbon, and protein and on its fiber and botanical characteristics (Buchanan et al., 1978a; Cull, 1983). On a scale of 5 (best)-17 (worst), the potential ofplant species as oil- and hydrocarbon-multipurpose-producing crops has been suggested but is considered far from absolute. All the species will be further screened for possible advanced study based on broader and more definitive criteria (Knowles et al., 1984). However, it is likely that most of the species finally selected will have ratings of < 11. Of the 100 Arizona species analyzed for this report, data is reported on 38, based on results described below.

Chemical analyses and ratings Analytical data and ratings are presented for (1) species with ratings ofless than 11, (2) species with a rating of 11, ifyields were at least 3.0% oil, or at least 15.0% polyphenol, or at least 0.4% hydrocarbon and/or at least 14.0% protein, and (3) species with ratings of greater than 11, if yields were at least 5.0% oil, 20% polyphenol, 0.6% hydrocarbon or 18.0% protein. Table 1 gives data for species with ratings of less than 11. Very high yields of oil were obtained from Asclepias linaria (8.7%), Rhus choriophylla (7.0%), and Juglans major (7.0%). These species also yielded substantial amounts of either polyphenol (20.0% for R. choriophylla) or hydrocarbon (1.9% for A. linaria). Yield ofpolyphenol is not one ofthe criteria used in rating species (Buchanan et al., 1978a) but is still considered an important factor in selecting species for additional study. Three other species ofthe 18 listed yielded substantial amounts of oil plus hydrocarbon. These were Pittosporum tobira (4.1% + 2.3%), Ganya wrightii (3.8% + 1.9%) and Cordia boissieri (3.6% + 1.2%). Of the 100 Arizona species collected, only G. wrightii, a gutta-producing species, has been previously collected and reported by our Center. That sample contained 2.7% oil and 0.4% hydrocarbon (Roth et al., 1985). Oenothera hookeri was fairly high in oil (5.6%) but low in other fractions. Other species listed gave moderate amounts of oil, polyphenol and hydrocarbon. Several species had very high protein contents, notably Solanum erianthum (21.7%), Atriplex elegans (20.9%), and Robinia neo­ mexicana (19.9%). Of the 600 species previously screened at this Center, none yielded as much oil plus polyphenol as Rhus choriophylla or as much oil plus hydrocarbon as Asclepias linaria. Only 6 of the 600 yielded more than 7% oil (7.1-11.2%). Of the 6, Euphorbia lathyrisL. from California yielded 9.9% oil + 10.0% polyphenol, 1985] CARR ET AL.: XEROPHYTES AS ENERGY SOURCES 509

TABLE 2. ANAL"YTICAL DATA OF SELECTED SPECIES WITH A RA.TING OF 11. a

Collector Family and Herbarium Polv. Hvdro- Pro~ Species collection .... oucher Oil phenol carbon tern Common name Type ofpIam area b number % 0',0 % % Bignoniaceae Chi/opsis linearis (Cav.) shrub H.P 80177 3.0 18.4 0.0 9.9 Sweet Desert willow Compositae Baccharis sarothroides shrub H.P 80387 1.6 18.1 1.0 9.2 Gray Desert-broom Gnaphalium leucocephalum herbaceous H,SC 80394 2.5 7.7 0.6 5.1 Gray perennial Cudweed Verbesina encelioides herbaceous M,P 80128 4.1 5.8 0.6 23.3 (Cav.) Benth. and Hook. annual Golden crownbeard Viguiera multiflora (Nutt.) herbaceous M,SC 80374 3.0 8.9 0.0 7.5 Blake perennial Showy goldenrod Labiatae Rosmarinus officinalis L. shrub M,P 80279 3.4 14.5 0.3 6.5 Rosemary Phy10laccaceae Rivina humilis L. herbaceous M,P 80224 4.8 4.0 0.1 19.8 Rouge plant perennial Pinaceae Pseudotsuga menziesii tree H,P 80369 3.2 18.7 0.0 5.6 (Mirbel) Franco var. glauca (Beissner) Franco Douglas fir Rosaceae Cowania mexicana D. Don shrub H,SC 80391 2.6 18.7 0.3 9.7 Quinine bush Pyracalliha Jorwneana shrub H,P 80287 3.4 7.6 0.0 12.0 (Maxim.) H. L. Li pyracantha Vauquelinia ca/((ornica shrub or tree M,P 80244 3.3 16.5 0.2 9.6 (Torr.) Sarg. Arizona rosewood Verbenaceae Lalliana camara L. shrub H,P 80389 1.8 9.3 0.2 20.1 Yellow sage

a.b See footnotes afTable 1. and Euphorbia dentata Michx. from Illinois yielded 11.2% oil + 4.1 % polyphenol. Both of these species were low in hydrocarbon (0.2-0.4%). About three-fourths of the 600 species were from central and southern Illinois. Data for the 12 selected species with a rating of II are shown in Table 2. There were 7 species with oil yields ranging from 3.0-4.8%, 5 species with polyphenol yields from 16.5-18.4%, and 3 species with hydrocarbon yields from 0.6-1.0%. Three species contained from 19.8-23.3% protein. Several of these species con- 510 ECONOMIC BOTANY [VOL. 39

TABLE 3. ANALYTICAL DATA OF SELECTED SPECIES WITH RATINGS GREATER THAN 11."

Collector Familv and Herbarium PolY. Hvdro­ Pro· Species collection voucher Oil phenol carbon tein Ral~ b 0' Common name Type of plant area number '0 % % % ing Aizoaceae Trianthema portula­ herbaceous M,P 80126 1.5 3.8 0.0 32.9 IS castrum L. annual Horse purslane Berberidaceae Nandina domestica shrub M,P 80248 1.8 21.9 0.0 9.9 12 Thunb. Heavenly bamboo Capparaceae Polanisia trachysperma herbaceous H,P 80178 4.6 6.1 0.0 14.9 14 Torr. and Gray annual Western clammyweed Compositae Heterotheca suba.;dllaris herbaceous M,P 80130 2.5 6.7 0.6 10.8 12 (Lam.) Britt. and annual or Rusby biennial Telegraph plant Loranthaceae Phoradendron coryae shrub H,SC 80386 2.7 30.2 0.2 5.2 15 TreJ. Mistletoe Martyniaceae Proboscidea parviflora herbaceous H,P 80180 3.8 9.6 0.1 29.3 13 (Wooton) Wooton and annual Standley Devil's claw Sapindaceae Dodonaea viscosa shrub or tree H,SC 80371 1.9 21.5 <0.1 6.1 12 (L.) Jacq. Hop bush Solanaceae Datura meteloides DC. herbaceous M,P 80241 1.6 10.0 0.0 20.0 12 Sacred datura perennial

...b See footnotes afTable I. tained noteworthy amounts of more than one fraction. These included Chi/opsis linearis (3.0% oil + 18.4% polyphenol), Baccharis sarothroides (I8.1% polyphe­ nol + 1.0% hydrocarbon), Verbesina encelioides (4.1 % oil + 0.6% hydrocarbon + 23.3% protein), Rivina humilis (4.8% oil + 19.8% protein), Pseudotsuga menziesii var. glauca (3.2% oil + 18.7% polyphenol), and Vauquelinia cali/ornica (3.3% oil + 16.5% polyphenol). Table 3 gives data for selected species with ratings greater than 11. Of these, Polanisia trachysperma and Proboscidea parviflora contained substantial amounts of oil (4.6 and 3.8%, respectively) and protein (14.9 and 29.3%, respectively). Trianthema portulacastrum was exceptionally high in protein (32.9%). Phora­ dendron cOlyae gave the highest polyphenol yield (30.2%) of the 100 analyzed. Several ofthe species listed in Tables 1-3 have been studied by others for their current and potential nonfood uses. These include Artemesia ludoviciana subsp. 1985] CARR ET AL.: XEROPHYTES AS ENERGY SOURCES 511

TABLE 4. CLASSES OF COMPOUNDS FOR PLANT OILS."

Esters Other free Free fatty Species Sterols alcohols acids Triglyceride Nonglyceride Hydrocarbon Asclepias linaria A A Ab NA' A A Cassia leptocarpa A A Ab A NA A Chi/opsis linearis A Ab Ab A NA A Cordia boissieri A A A A NA A Erythrina flabelliformis AAAA NA A Garrya wrightii A A Ab A A A Juglans major AAAA NA A Oenothera hookeri A A AA NA A Pittosporum tobira A AAA A A Polanisia trachysperma AAAA Ab A Proboscidea parviflora A AAA NA NA Pseudotsuga menziesii AAA Ab Ab A pyracantha!ortuneana A AA Ab NA A Rhus choriophylla A A A Ab Ab A Rivina humilis A AAA NA A Rosmarinus officinalis AAA Ab NAc A Vauquelinia cal£fornica A A A A A NA Verbesina encelioides A AAA Ac NA Viguiera multiflora AAA Ab NA A

... Classes were indicated by thin layer chromatography (TLC). A = apparent (TLC spot found ncar standard reference compound). NA = nOl apparent (no TLC spot found near reference compound). b Very weak TLC spot. e TLC spot found for possible triterpenol.

albula, Jatropha cardiophylla, Cassia leptocarpa, Rosmarinus officinalis, Chi­ lopsis linearis, Baccharis sarothroides, and Proboscidea parviflora (Davis et aI., 1983).

Classes ofoil lipids Procedures used to identify classes oflipid constituents in whole-plant oils have been discussed recently (Carr, 1985). Rr values of oil constituents and of sapon­ ifiable and unsaponifiable constituents, after saponification ofthe oil, were com­ pared to those ofa standard mixture ofcompounds (sitosterol, oleyl alcohol, oleic acid, triolein, oleyl laurate, and squalene). Overall results suggested that oils of all species listed in Table 4 contained sterols, other free alcohols less polar than sterols, free fatty acids, and esters. Two oils had very weak TLC spots for non­ glyceride esters. Eleven of the 19 oils apparently had no nonglyceride ester. Oils of 3 species had spots with R r values between those of triolein (triglyceride) and oleyllaurate (nonglyceride ester), possibly triterpenols (Buchanan et aI., 1978b). All but 3 ofthe 19 oils had small amounts ofsome type ofhydrocarbon (squalene reference).

Oil saponification Table 5 shows yields ofunsaponifiable matter (UM) and free acids (FA) obtained from saponified oils. About 63% of the 19 saponified oils had more than 40% UM (% of purified plant oil), 53% had more than 50% UM, and 26% had more 512 ECONOMIC BOTANY [VOL. 39

TABLE 5. OIL SAPONIFICATION DATA.

oil fractions Species Unsaponifiable matter Qc)'1. Free acids %~ Asclepias linaria 61.4 3.4 Cassia leptocarpa 46.1 30.3 Chi/opsis linearis 22.5 51.6 Cordia boissieri 66.0 29.1 EIJ,thrina flabell{formis 42.9 47.5 GarlJ'a wrightii 53.6 27.4 Juglans major 34.5 57.4 Oenothera hookeri 4.5 66.0 Pittosporum tobira 33.4 38.2 Polanisia trachysperma 10.1 54.8 Proboscidea parviflora 14.8 57.7 Pseudotsuga menziesii 49.3 29.8 Pyracantha fortuneana 62.8 14.3 Rhus choriophylla 62.8 27.8 Rivina humilis 44.6 31.7 Rosmarinus officinalis 75.2 17.7 Vauquelinia cal{fomica 57.7 22.9 Verbesina encelioides 47.7 3.7 Viguiera multiflora 16.8 62.4

;l Percent ofentire, above~ground plant oil. than 60% UM. Those with more than 60% UM were Rosmarinus officinalis (75.2%), Cordia boissieri (66.0%), Rhus choriophylla (62.8%), Pyracanthafortu­ neana (62.8%), and Asclepias linaria (61.4%). Five of the saponified oils were unusually low in UM (4.5-22.5%). TLC data indicated that these oils were high in saponifiable triglycerides. Percentages of the 19 species with more than 40% UM were similar to those for previously analyzed oils (Carr, 1985). The combined amounts of UM + FA from saponified oils are usually in the range of 70-90% of the plant oils. Amounts of UM + FA were 90-95% for 5 of the 19 oils, 71-80% for 10 ofthe oils, and less than 70% for 4 of the oils. These amounts are dependent to a large extent upon the amounts of polar organic material removed by partitioning from the FA fractions before drying and weigh­ ing these fractions and on the amounts ofvolatile components lost from the UM and FA fractions during oven drying (l05°C, 2 h).

Analyses ofhydrocarbon fractions Twelve species that yielded at least 0.4% hydrocarbon were analyzed by infrared (IR) spectroscopy and gel permeation chromatography (GPC). IR spectra showed that 11 of these hydrocarbon fractions contained cis-l,4-polyisoprene (rubber) substantially contaminated with waxes. Hydrocarbon from GanJla wrightii con­ tained essentially all trans-l,4-polyisoprene (gutta) and no detectable rubber, as indicated by carbon-13 nuclear magnetic resonance. IR spectra of plant rubber, gutta, and waxes have been discussed previously (Buchanan et aI., 1980; Roth, 1985; Carr, 1985). The 12 hydrocarbon fractions were analyzed for weight average molecular weight 1985] CARR ET AL.: XEROPHYTES AS ENERGY SOURCES 513

(M,J by GPC (Swanson et aI., 1979; Carr, 1985). M" could not be determined for 7 of the 12 hydrocarbon fractions because the rubber was poorly resolved (separated) from other low-mo1ecu1ar-weight material (primarily waxy materials).

Of the 5 hydrocarbon fractions resolved, Mw was 131,000 for Garrya wrightii (gutta), 109,000 for Cordia boissieri, 101,000 for Asclepias linaria, 49,000 for Guardiola platyphylla, and 27,400 for Pittosporum tobira. It is likely that M".'s ofpolyisoprenes ofthe unresolved hydrocarbon fractions were under 25,000. Mw's ofrubber from guayule and Hevea samples previously analyzed at our Center by GPC were 1.28 million and 1.31 million, respectively.

ACKNOWLEDGMENTS

We thank Professor Robert W. Hoshaw, Department of Ecology, University of Arizona, Tucson, AZ, and Charles T. Mason, Jr., Curator of Herbarium. University of Arizona, for plant collections. Irene M. Cull for botanical information used in rating species, Charles L. Swanson for GPC analysis, and Larry W. Tjarks for l3C NMR analysis.

LITERATURE CITED

Buchanan, F. H., 1. M. CulL E H. Otey, and C. R. RusselL 1978a. Hydrocarbon- and rubber­ producing crops. Evaluation of U.S. plant species. Econ. Bot. 32: 131-145. ---, F. H. Otey, C. R. Russell, and 1. M. CulL 1978b. Whole-plant oils, potential new industrial raw materials. J. Amer. Oil Chern. Soc. 55: 657-662. ---, and J. A. Duke. 1981. Botanochemical crops. In O. R. Zaborsky, T. A. McClure, and E. S. Lipinsky, ed, CRC Handbook of Bisolar Resources, VoL 2, p. 157-179. CRC Press, Boca Raton, FL. ---, F. H. Otey, and M. O. Bagby. 1980. Botanochemicals. In T. Swain and R. Kleiman, ed, Recent Advances in Phytochemistry, VoL 14, p. 1-22. Plenum, New York. Bungay, H. R. 1982. Biomass refining. Science 218: 643-646. Calvin, M. 1983. New sources for fuel and materials. Science 219: 24-26. Carr, M. E. 1985. Plant species evaluated for new crops potentiaL Econ. Bot. 39: 336-345. Cull,!. M. 1983. Midwest plants for potential crops. Trans. Illinois State Acad. Sci. 76: 203-212. Davis, J. B., D. E. Kay, and V. Clark. 1983. Plants tolerant of arid, or semi-arid, conditions with non-food constituents ofpotential use. In Report ofthe Tropical Products Institute, G 150, p. 1-172. Tropical Products Institute, London. Knowles, P. E, K. J. Lessman, and 21 other task force members. 1984. Development ofnew crops: Needs, procedures, strategies, and options. In Council for Agricultural Science and Technology, Report No. 102, p. 1-30. Headquarters Office, Ames, IA. Princen, L. H. 1983. New oilseed crops on the horizon. Econ. Bot. 37: 478-492. Roth, W. B., 1. M. Cull, R. A. Buchanan, and M. O. Bagby. 1982. Whole plants as renewable energy resources: Checklist of 508 species analyzed for hydrocarbon, oil, polyphenol, and protein. Trans. Illinois State Acad. Sci. 75: 217-231. ---, M. E. Carr, E. A. Davis, and M. O. Bagby. 1985. Garrya;7avescens S. Wats. and G. wrightii Torr.: New sources ofgutta-percha. Phytochemistry 24: 183-194. Swanson, C. L., R. A. Buchanan, and E H. Otey. 1979. Molecular weights ofnatural rubbers from selected temperate zone plants. J. AppL Polym. Sci. 23: 743-748.