59^ 



A TEXT-BOOK OF BOTANY. 



resin exists in the plant in the form of an emulsion which readily 

 blackens with the alkali hydroxides. So delicate is this reaction 

 that minute amounts of the substance may be detected by means 



FIG. 328. Leaves and fruit of the poison ivy (Rhus radicans). This is a 3-foliate com- 

 pound leaf, the leaflets being ovate and having veins which bifurcate and end free. 



of the microscope if the plant tissues are mounted in an alcoholic 

 solution of potassium hydroxide. A vesicating principle CARDOL 

 is found in the CASHEW NUT. The latter is the fruit of Anacardium 



