" INTRODUCTION, 

 —coo- 

 Plants belonging to the natural order Anacardiaoiae 

 (Cashew :^ily or Sumach family) are found in all the tem- 

 perate oliinates of the world and quite frequently in semi- 

 tropical climates. Many of these plants play important 

 parts in economic botany, yielding dye-stuffs, tanning 

 material, wax, varnish, and drugs. Several species are 

 poisonous. At least three poisonous species of the genus 

 RHUS are found in the United States. These three are all 

 common and well known plants, but confusion frequently 

 arises concerning them on account of the different names 

 by which they are known in different localities. For 

 example, poison ivy ( Rhus toxicodendron or Rhus radicans ) 

 probably the best known poisonous plant in America, being 

 found in all the 3tates except those in the extreme West, 

 is often confounded with and popularly called "poison oak". 

 The true poison oak is the Rhus diversiloba of the Western 

 States. The third and most poisonous species of this 

 plant is Rhus veneiyata or Rhus vemix ; it is the Rhus 

 vemicifera of Japan, from which Japanese lao is obtained. 

 It is popularly known in the United States as "poison 

 elder". It grows in swamps from Canada to Florida, 



1. Chesnut. Bull. Ho, 20, U. 3. Dept. of Agr. , Div, 

 of Botany. 



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