POISON IVY. 23 
frequently observed individual shoots from the 
same stock haying the charaeters of both varieties, 
I have also observed that young plants of Rhus 
radicans frequently do not put out rooting fibres 
until they are several years old, and that they 
seem, in this respect, to be considerably influ- 
enced by the contiguity of supporting objects. 
_ The wood-of the Poison Ivy is brittle, fine 
wiliindegia _— sesh mpesdenseanage 
plants. | i ae 
If a leaf or stem of this lant he guru off, 
a yellowish milky juice immediately exudes from 
the wounded extremity. After a short exposure 
to the air, it becomes of a deep black colour and 
does not again change. This juice, when applied 
to linen, forms one of the most perfect kinds of 
indelible ink. It does not. fade from age. 
washing, or exposure to any of the common 
chemieal agents. I have repeatedly, when in 
the country, marked my wristband with spots of 
this juice. The stain was at first faint and 
hardly perceptible, but in fifteen minutes it 
became black, and was never afterwards eradi- 
eated by washing, but continued to grow: darker 
as long as the linen lasted. 
Dr. Thomas Horsfield, in his. eilunblé: ingle 
tation on the American species of Rhus, made 
