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AMERICAN JOURNAL OF BOTANY 
[Vol. 8 
about twelve hours or more after exposure. This long period of latency is 
much against the supposition that the poison is volatile. It would be 
much easier for a volatile poison to evaporate and diffuse through the 
atmosphere in twelve hours if it required a dozen hours to penetrate the 
skin. 
From the preceding experiments, it is clear that the poison is non-volatile. 
But we still have the question to answer as to how poisoning occurs without 
contact with the plant. This question has been studied by Von Adelung 
(46), Schwalbe (43), Hubbard (17), Hadden (16), and Frost (15). 
Von Adelung considered the pollen to be toxic and disseminated by the 
wind. As a matter of fact, the pollen may be rubbed on the skin of a sus- 
ceptible person without ill effects. The skin may even be lacerated. 
The pollen grains, although small enough to be carried by the wind, have 
no wing-like projections or tissues which would aid their flight, but on the 
contrary are covered with a sticky substance which tends to hold them in 
masses to the flower. Pollination is effected by insects. Similar non-toxic 
results have been obtained with the pollen of other poisonous species of 
Rhus; with that of R. vernicifera by Inui (21), that of R. Vernix by Warren 
(48), and that of R. Toxicodejidron by Rost and Gilg (40). 
Schwalbe (43) attributed poison transmission to the trichomes of the 
plant. The trichomes are very minute and are found in abundance on the 
young stems and on the under surfaces of the leaves. The trichomes 
were considered to be poisonous and carried by the wind. 
In an investigation of this theory, fresh leaves were placed in an alembic, 
and a current of air was blown through. The outcoming air current was 
caused to impinge on the skin of a susceptible individual. No dermatitis 
resulted. The experiment was repeated, except that the outcoming air was 
caused to bubble for several hours through alcohol in which the poison is 
soluble. This alcoholic solution was concentrated and found to be non-toxic. 
In another experiment, the hairy side of an uninjured leaf (previously 
examined carefully with a hand lens for the absence of droplets of sap) was 
drawn across the skin with no ill effects. In another test an uninjured 
leaf was placed in 95 percent alcohol at room temperature for ten minutes. 
The alcoholic solution was concentrated and found to be non-toxic. 
Rost and Gilg (40) carried on experiments with R. Toxicodendron to 
determine if the plant hairs drop off spontaneously, if they can be blown off 
from cut twigs, and if the poison, as in Primula obconica, can be obtained 
by contact from the under sides of the leaves. Two shells containing gly- 
cerine were placed under Rhus plants for two windy days in May. When 
this liquid was examined microscopically after the experiment, needle- 
shaped and club-shaped hairs were found. On October 17, 1-911, three 
wide glass dishes containing glycerine water were placed under thickly 
leaved branches of R. Toxicodendron. These were left for four days. 
A microscopical examination on October 21 showed no hairs in the dishes. 
