Poison ivy, with the possible exception of ragweed, is assuredly, from the medical point of view, the biggest plant nuisance in this country. Botanically, poison ivy belongs to the Anacardiaceae, which is a large family, most of whose members are tropical or sub-tropical. Many useful plants are included in this family; among them are the cashew nut (Anacardium occidentale), the marking nut or Indian ink tree (Semecarpus anacardium), the pistachio nut (Pistacia vera), the mango (Mangifera indica), the lacquer tree (Rhus verniciflua). There are, of course, many other members to this family, many of which are quite ornamental, such as some of the sumachs. In this country there are two "poisonous" members of this family, namely, poison ivy and poison sumach.*Poison ivy is the name given to a group of closely related plants of diverse leaf appearance and growth habit which are botanically known as