120 ANACARDIACEJE. 



This common and, by many people, much- dreaded plant occurs in two 

 rather distinct forms, which were formerly considered separate species, 

 but are now recognized as specifically identical, their differences being due 

 entirely to the circumstances of their growth. A plant growing in an open 

 space with no convenient support near has the habit of a low shrub ; while 

 one rooted at the base of a tree or beside a rock puts forth innumerable 

 adventitious rootlets, and by means of these climbs upward vigorously, 

 never stopping, under favorable circumstances, until it has reached the 

 highest point attainable. Another curious feature in the growth of the 

 plant as a climber is that the increase in the thickness of the stem takes 

 place almost entirely upon the side next the support, whether this be a 

 rock, tree, or any other object, so that the pith is eccentric. As the root- 

 lets bring no nourishment to the stem, and as they are put forth in quantity 

 only when there is something near to fix themselves to, it appears probable, 

 as the author endeavored to show some years ago, that they are produced 

 by the mere stimulation of contact ; and also that the increased growth 

 on the side of the stem next the support is induced in the same manner. 

 The climbing plant was formerly denominated R. radicans, a name, of 

 course, now discarded. 



Habitat. — Common everywhere from Canada to the Gulf of Mexico and 

 westward. 



Rhus venenata De Candolle. — Poison Sumac, Poison Eider. 



Description. — A vigorous shrub, 6 to 18 feet high, with smooth, pale 

 gray bark. Leaflets in 3 to 6 pairs, with an odd terminal one, obovate- 

 oblong, entire. Panicles larger than in the preceding species ; fruit also 

 larger, greenish-yellow or greenish-white. 



Habitat. — Common in swamps and wet places from Canada to Florida 

 and westward. 



Part Used. — The fresh leaves of Rhus Toxicodendron — United States 

 Pharmacopoeia. The leaves of R. venenata possess similar properties. 



Constituents. — These species of rhus, together with R. diver siloba Tor- 

 rev and Gray of the Pacific Coast and R. pumila Michaux of the Southern 

 States, comprise the poisonous members of the genus indigenous to North 

 America. Their poisonous properties, though differing in degree, are es- 

 sentially identical in quality. R. pumila is said to be the most poisonous 

 of the group, while R. venenata occupies a second place, being itself con- 

 siderably more violent in action than R. toxicodendron or R. diver siloba ; 

 the two last-named resembling each other very much both in habit of 

 growth and in their effects. The poisonous constituent of these plants, 

 though considerably investigated, has not been as yet thoroughly charac- 

 terized. That it is volatile is well known, and that it is an acid principle 

 has also been demonstrated ; but beyond this nothing is definitely known. 

 Though volatile and capable of producing its peculiar effects upon very 

 susceptible individuals, even at some distance from the growing plants, it 



