506 WOODY PLANTS OF MASSACHUSETTS. 



be procured from it. To this end, Dr. Bigelow made, in 1815, 

 several experiments, which seem to establish this point in a 

 manner very satisfactory. 



" A quantity of the juice was boiled alone, until nearly all the 

 volatile oil had escaped, and the remainder was reduced almost 

 to the state of a resin. In this state, it was applied while warm 

 to several substances, which, after cooling, exhibited the most 

 brilliant, glossy, jet black surface. The coating appeared very 

 durable and firm, and was not affected by moisture. It was 

 elastic and perfectly opaque, and seemed calculated to answer 

 the purposes of both paint and varnish." — Med. Bot., I, 101-2. 



The poisonous property, as in most cases of vegetable poisons, 

 seems to be removed by evaporation or boiling ; and the dry 

 varnish would probably be innocuous. 



Sp. 5. The Poison Ivy. R. toxicodendron. L. 

 Figured in Bigelow's Medical Botany, III, Plate 42. 



R. toxicodendron and radlcans of Linnaeus and other au- 

 thors. When climbing over rocks or on the trunks of trees, it 

 seems to have been considered R. radlcans ; when standing by 

 itself, and forced to erect a portion of its stem, R. toxicodendron. 

 I have never been able to find a precise distinction between the 

 several forms of this plant, which pass into each other, and am 

 glad to see that they are considered by Torrey and Gray as 

 only varieties. 



The Poison Ivy is a hardy plant, frequent in moist or shady 

 places, climbing over rocks to which it attaches itself by numer- 

 ous radicles which penetrate the investing lichens, or over 

 bushes and along the trunks of trees, often to a great height, 

 fastening itself to the bark so firmly that it breaks more readily 

 than it is detached, and so closely as to impede the growth of 

 the plant. 



The leaves are in threes, on a petiole sometimes perfectly 

 smooth, sometimes downy, flattened above. The leaflets are 

 smooth and shining on both surfaces, broad-ovate, acuminate, 

 entire or variously and irregularly toothed and lobed ; the lateral 

 ones nearly sessile, broader below, the terminal on a stalk six to 

 eighteen lines long, or sometimes closely sessile. The sterile 



