POISON IVY 403 



oblique and the cells not infrequently contain rod-shaped crystals; 

 some of the intermediate cells of the hairs may be collapsed and 

 the reddish cell sap of all the cells of the hair may contain one or more 

 air bubbles; fragments of endosperm frequent. Mounts in solutions 

 of aniline sulphate and sulphuric acid stain the stone cells yellow, 

 these are very small and possess irregularly thickened walls; frag- 

 ments of embryo with rather small cells containing a fixed oil; occa- 

 sional reddish colored fragments of epidermis and underlying spiral 

 tracheae of the mesocarp. 



On mixing 1 gm. of powdered Rhus glabra witn 10 c.c. of hot 

 water, shaking occasionally until cold and filtering and evaporating 

 the solution in a watch crystal spontaneously, there should separate 

 numerous feather-shaped crystals of Gallic Acid which polarize 

 strongly with a distinct play of colors. 



Constituents. Tannic acid about 2 per cent; gallic acid, and 

 acid calcium and potassium malates. The percentage of acidity in 

 the fruits, in terms of malic acid, varies from 6.5 to 8 per cent. 



Allied Plants. The fruits of the staghorn sumac, Rhus typhina, 

 a shrub very abundant in the eastern United States, have replaced 

 to some extent the fruit of Rhus glabra. The drupes of these two 

 plants closely resemble each other both in form and size, but the 

 latter are distinguished by being covered with long, nearly straight, 

 needle-like, crimson hairs. These hairs are frequently over 2 mm. 

 in length, more or less undulate in outline and have relatively thicker 

 walls. The constituents of Rhus typhina are probably similar to 

 those of Rhus glabra, the total acidity in terms of malic acid 

 ranging from 7.8 to 11.22 per cent, being much higher than in 

 R. glabra. 



Allied Drugs. The leaves of Rhus glabra contain from 16 to 25 

 per cent of tannin. The galls formed on the petioles and leaves 

 resemble the Chinese or Japanese galls and contain about 60 per 

 cent of tannin and some gallic acid. 



Literature. Kraemer, Amer. Jour. Pharm., 1913, p. 398. 



RHUS TOXICODENDRON. Poison Ivy or Poison Oak. The fresh 

 leaflets of Rhus Toxicodendron (Rhus radicans), a woody vine belong- 

 ing to the Anacardiacese, common in hedge rows, along fences and in 

 thickets throughout the United States. The plant varies consider- 

 ably and one or more distinct varieties are recognized. It either 

 trails over the ground, or climbs by means of aerial roots, sometimes 

 becoming quite shrublike (Fig. 173). 



The leaves are 3-foliate, the leaflets being ovate, acuminate, 

 nearly entire, inequilateral and with short stalks; the flowers are 



