Apr., 1921] 
MCNAIR RHUS DIVERSILOBA 
181 
crystal clusters, presumably of calcium oxalate, occur in the palisade 
parenchyma. The cells of the lower epidermis are similar to those of the 
upper epidermis but smaller; stomata are very frequent and apparently 
absent from the ridges. The leaves wilt very easily. It is hardly possible 
to bring a cut branch from the field to the laboratory without observing 
wilting. There are two kinds of trichomes on the leaves, multicellular 
club-shaped, and unicellular or multicellular bristle-shaped (21). 
The thick-walled bristle hairs occur mainly on the lower side on the 
ridges, large and small, of the leaf, although they are found also in fewer 
numbers on the upper side in corresponding places. The club-shaped 
trichomes, on the other hand, are found mostly between the ridges of the 
leaves. These two different forms of trichomes are similar to those found 
by Mobius (22) on Rhus vernicifera L. and by Rost and Gilg (24) on Rhus 
Toxicodendron L. Morphologically the club-shaped hairs seem to be 
glandular: first, because 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 the floral 
region and the leaves, less on the green stem, and hardly at all on the 
woody portion. Schwalbe (25, 26) considered the poison of Rhtis diver siloha 
to be excreted from glandular hairs on the surface of the plant. That such 
is not the case can be shown by the two following experiments : 
(1) When the green stem, pedicel, or main ribs of the leaf, which are 
covered with trichomes, are rubbed on sensitive skin, 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. 
(2) The fresh green leaves were placed in a fmger bowl and soaked at room 
temperature in 95 percent alcohol for 10 minutes. The leaves had been 
examined first under a hand lens to make sure that through possible injury 
no resinous sap was on the surface. When placed in the finger bowl the 
sap was prevented from running down the pedicel from the cut end into 
the alcohol. The leaves when taken out of the alcohol had lost their gloss. 
The pale yellowish alcoholic solution remaining was concentrated by boiling 
in an open beaker. It was found to be non-toxic. It was not darkened by 
potassium hydroxide, nor did it respond to other chemical tests for the 
poison. These results indicate that neither the plant trichomes nor their 
exudate is poisonous. 
The club-shaped hairs are so minute as to be hardly discernible by the 
naked eye. They have a length of 0.071 mm. and a maximum breadth of 
0.0027 mm. Under the microscope they exhibit a clear, unicellular basal 
portion as an outgrowth of an epidermal cell, above which are the numerous 
cells that go to make up the main portion of the hair. The cells of the main 
portion when viewed transversely radiate from a longitudinal central axis. 
The apex terminates in a single cell, and the entire main portion of the hair 
