668 CONTEIBUTIONS FROM THE NATIONAL. HERBARIUM. 



Low shrub or often a large woody vine, the stems clinging to trees by- 

 aerial roots; leaves deciduous, the 3 leaflets ovate or rhombic, 5 to 12 cm^ 

 long, acute or acuminate, entire or irregularly dentate, pubescent or nearly 

 glabrous; flowers green, in loose axillary panicles; fruit globose, 3 to 5 mm. 

 in diameter. "Chechen" (Yucatan, Urbina) ; " hiedra " (Sinaloa, Nueva 

 Le6n, Tamaulipas, Durango) ; "mala mujer " (Veracruz, Jalisco, San Luis 

 Potosl) ; "mexye" (Otoml, Buelna) ; " guardalagua " (Jalisco); " hincha- 

 huevos " (Veracruz); "bemberecua" (Michoae^n, Tarascan) ; " guau " (Rami- 

 rez) ; "hiedra mala" (Michoacan). The English name is "poison ivy." 



The species is a variable one, as might be expected from its wide range, and 

 many segregates have been described, but it is impossible to determine their 

 value until the group has been studied more critically than has been attempted 

 heretofore. Both the dwarf and the scandent forms occur in Mexico. 



Poison ivy and its effects are well known throughout the range of the 

 plant. All parts contain a nonvolatile oil, toxicodendrol, which is the active 

 principle. Contact with the plant, or even one's presence in its vicinity if it 

 is covered with dew, produces painful swelling of the parts affected and an 

 eruption of the skin. Some persons are very susceptible to the poisonous 

 effects of the plant, while others are not affected at all. Those who are 

 immune may, it is said, later become susceptible to it. Poisoning by the plant 

 is painful and ofter dangerous, especially if the eyes are affected. Many 

 remedies have been suggested, the most widely used, perhaps, being the 

 application of an alcoholic solution of lead acetate. An extract of Orindelia 

 (family Asteraceae) has been used successfully. In Mexico various remedies 

 are reported, among them being a decoction of Eeimia salicifolia and Lobelia 

 ■fulgens ("cresta de gallo").^ 



The leaves were formerly official in the U. S. Pharmacopoeia. The juice 

 is milky and turns black on exposure to air ; upon linen it leaves an indelible 

 stain. The plant has been used as a local irritant, but is no longer employed. 

 A tincture is used by homeopathic practitioners as a remedy for rheumatism. 



The plant is mentioned by Clavigero (Historia de la California, 17S9) under 

 the name " hiedra maligna." 



8. Rhus eximia (Greene) Standi. 



Toxicodendron eximium Greene, Leaflets 1: 123. 1905. 



Durango, Nuevo Le6n, and Tamaulipas; type collected near the city of 

 Durango. 



Low shrub ; leaflets rhombic, 4 to 9 cm. long, usually 3-lobed, the lobes again 

 shallowly lobed, densely pubescent beneath or glabrate. " Hiedra " (Tamauli- 

 pas). 



Perhaps only an extreme form of R. radicans. The type is densely pubes- 

 cent, and a Tamaulipas specimen referred here is glabrate. The latter may 

 represent a distinct species. 



9. Rhus microphylla Engelm. ; A. Gray, PI. Wright 1 : 31. 1S52, 

 Rhoeidium microphyllum Greene, Leaflets 1: 143. 1905. 

 RJioeidium retuaum Greene, Leaflets 1: 144. 1905. 

 Rhoeidium potosinum Greene, Leaflets 1: 144. 1905. 

 Rhoeidium cinereum Greene, Leaflets 1 : 144. 1905. 



* For a very full account of the poisonous properties of the plant and of the 

 remedies which have been suggested (over 200 of them), see W. L. McAtee, An 

 account of poisonous sumachs, Rhus poisoning, and remedies therefor, Medical 

 Record (New York), May 8, 1920; see also E. P. Smith, Plant dermatitis, Journ. 

 Bot. Brit. & For. 58: 130-135. 1920. 



