LOCO WEEDS AND OTHER POISONOUS PLANTS 8 1 



that the wind blowing toward a person from a patch of poison ivy is suffi- 

 cient to produce the usual rash on the skin of susceptible persons, but in 

 all likelihood such persons have crushed the plant under foot and in re- 

 moving their shoes before going to bed have removed the active principle 

 from the surface of the leather. They may also have inadvertently 

 touched the plant in passing by it. The smoke from brush fires in which 

 poison ivy has been placed will cause inflammation of the skin of face and 

 hands. Susceptible persons in our large department stores, who unpack 

 lacquer ware imported from Japan, frequently have the characteristic 

 dermatitis, as the lacquer is made from the juice of a Japanese sumach, 

 Rhus vernicifera, and the toxic oil is partially freed from the surface of the 

 lacquered objects during their transportation in closed cases in which 

 steaming may occur from one country to another in the holds of ocean 

 steamers. The southern shrub, Rhus Toxicodendron, was formerly con- 

 sidered to be identical with the poison ivy, but recently the two species 

 have been separated as Rhus radicans and Rhus Toxicodendron. The 

 poison ivy ranges from Nova Scotia to Minnesota, Florida, Arkansas and 

 Nebraska, while the shrubby, Rhus Toxicodendron, the poison oak, is 

 found from North Carolina south to Florida and southwestward to Texas. 



A third shrub, known as poison sumach, poison oak, poison elder, 

 poison dogwood, thunder-wood, is Rhus Vernix which is found in swamps 

 from Ontario and Minnesota south to Florida and Louisiana. It is more 

 virulent than the other two species mentioned above. It grows to be a 

 small freely branching tree. It has large pinnately compound leaves, 

 panicles of greenish yellow flowers and large, white, shining drupes pro- 

 duced in open clusters. The California poison ivy, Rhus diiiersiloba is 

 found on the 'Pacific Coast from California to Washington. It is an 

 erect, or climbing, nearly smooth shrub with compound leaves of three to 

 five leaflets and flowers in loose axillary panicles with white fruit. A key 

 will enable one to distinguish these four species of Rhus. 



Eastern and Southern Species. 



A. Leaves trifoliate; vines or low shrubs. 



Vine climbing by aerial roots. 



Drupes 5-6 mm. in diameter. Rhus radicans 

 Upright shrubs. 



Drupes 6-7 mm. in diameter Rhus Toxicodendron 



B. Leaves pinnately 7-11 leaflets; tall shrub, or small tree Rhus 



Vernix. 



