320 



BOTANY AND PHARMACOGNOSY. 



spatula. The grayish-white emulsion is strained and on exposure 

 to air it changes to brown becoming finally black. This change 



Fig. 163. Leaves and fruit of the poison ivy {Rhus radicans). This is a 3-foliate com- 

 poundleaf, the leaflets being ovate and having veins whicU bifurcate and end free. 



is due to the oxidizing enxyme laccase. The natural lac (Ki- 

 urushi) contains a non-volatile poisonous resin-like principle 



