Mar., 1921] 
MCNAIR A STUDY OF RHUS DIVERSILOBA 
Seattle, F. S. Hall. 
Tacoma, seashore and bluffs, F. L. Pickett. 
Union City, F. L. Pickett. 
VANCOUVER ISLAND 
Vancouver Island, Tolmic, Douglas in Kew Herbarium. 
Victoria, near Swan Lake and on the west side of Seanich Arm, J. R. Anderson. 
The Origin and Occurrence of the Poison 
The freshly exuded resinous sap of R. diversiloba has long been known 
to be capable of producing dermatitis when applied to the skin. With this 
in mind, investigations were carried out to see whether the poisonous portions 
of the plant are limited to those portions that contain the resin canals. 
Microscopical examination of the staminate flower shows four resin 
ducts in the receptacle and pedicel, one in each petal, but no resin ducts 
more than half-way up the basal filaments of the stamens. Realizing the 
absence of resin canals in the anthers, it was thought perhaps the pollen 
might be non-toxic. (See PI. II, D.) The pollen was collected by shaking 
the flowers over a glass funnel to the stem of which a test tube was attached. 
This pollen was found to be non-poisonous when rubbed into the skin of an 
individual sensitive to the poison. An alcoholic extract of the pollen was 
non-toxic, nor did the pollen or the alcoholic solution assume a dark brown 
color when treated for five minutes with potassium hydroxide as does the 
poison. It is concluded, therefore, that the pollen is incapable of producing 
dermatitis. Similar non-toxic results have been obtained with the pollen 
of Rhus vernicifera by Inui (30), with that of R. Vernix by Warren (59), 
and with that of R. Toxicodendron by Rost and Gilg (50). 
C. Schwalbe (51) considered the poison of R. diversiloba to be excreted 
from glandular hairs on the surface of the plant. As the resin canals are 
not connected with the epidermis or with the trichomes, it was considered that 
these like the stamens might also be non-toxic. Two different forms of 
trichomes have been noticed on the plant, similar morphologically to those 
found by Mobius (42) on R. vernicifera and by Rost and Gilg (50) on R. 
Toxicodendron; namely, a unicellular or multicellular needle-shaped hair, 
and a multicellular club-shaped hair (PI. II, F). Morphologically the 
club-shaped hairs seem to be glandular; first, the upper multicellular portion 
is sharply marked off from the basal portion, which resembles a stalk; 
second, the upper portion has thinner walls than the basal portion; third, 
they are found mostly on the young, rapidly growing organs of the plant, 
especially on the floral region and the leaves, less on the green stems, and 
hardly at all on the woody portions. 
When the green stem, pedicel, or main ribs of the leaf, which are 
covered with trichomes, are rubbed on skin sensitive to the poison, no 
dermatitis results. Care must be taken, however, that the epidermis of 
the plant is not broken severely enough to cause the resinous sap to exude. 
The fresh green leaves were placed in a finger bowl and soaked in room 
