THE noxious saps of numerous members of the Anacardiaceae, such as Japanese lac, poison ivy, cashew nut shell liquid, etc., contain phenolic bodies carrying long unsaturated side-chains attached to the benzene ring. Earlier investigators1 have in certain cases established the length and the position of these alkenyl side-chains; but prior to the present investigation only very limited information was available concerning the structural details of the unsaturation. There is no doubt, however, that the unsaturation in the side-chain plays an important part both in the physiological properties2 and industrial uses3 of these compounds.