THE AMERICAN BOTANIST. 95 
as soon as the plant commences to grow, and that when they are,, 
they are formed of what are regarded as arrested branches — some- 
what analogous to the way in which the ''apples" are formed on 
the Azalea. Other nightshades have not the tuber-bearing habit. 
If the potato is likely to be due to a specific microbe, then almost 
certainly the tubers of the ground nut (Apios tiiherosa) must be 
placed in the same class, and probably the artichoke (Helianthus) 
also. 
The Poisonous Principle in Rhus. — Several attempts have 
been made to isolate the poisonous principle of the poison ivy 
(RJnis toxicodendron) and poison sumac (R. venenata^ and the 
resultant failures have given ground for the belief that it is a vola- 
tile substance difficult to secure. Later, an experimenter attrib- 
uted the poisoning to a volatile acid which he named toxicodendric 
acid. Still later researches go to prove that the real poison is an 
oil which is known as ''toxicodendrol." The oil is found in all 
parts of the plants and at all seasons ©f the year. Even the hairs 
of the leaves under the microscope may be seen to contain oiL 
The popular idea that the plant is most poisonous when in bloom 
may thus possibly have some foundation in fact, as the pollen 
might be carried for some distance by the wind. It is difficult in 
this case, however, to understand why the nose and throat are not 
more frequently affected. Toxicodendrol is insoluble in water, but 
readily dissolves in alcohol, ether, chloroform, etc. It is poison- 
ous in the minutest quantities. In one instance the one-thou- 
sandth part of a millegram in two drops of olive oil was effective. 
The oil is not volatile. The time necessary for it to take effect af- 
ter reaching the skin, varies from i8 hours to nine days. As 
the oil forms a nearly insoluable precipitate with lead acetate, the 
best remedy is seen to be the well known one of washing the af- 
fected parts with an alcoholic solution of lead acetate. The arti- 
cle from which these facts are drawn was published in Rhodora 
for March. 
