May, I92I] MCNAIR — TRANSMISSION OF RHUS POISON 
The preparations contained considerable dust. From the results of these 
experiments, it is evident that the hairs do not drop off to any great extent 
spontaneously at either the beginning or the end of the vegetative period. 
To determine whether or not the trichomes could be forcibly blown off, 
five experiments were conducted in 1911: 
A. At the end of July (Exp. S. i and 2) ; 
B. At the end of August (Exp. S. 3) ; 
C. At the end of September (Exp. S. 4) ; 
D. After the middle of October (Exp. S. 5). 
A branch was firmly fastened within a rectangular glass case (100 X 75 X 
180 cm.) and was exposed to an air current of about 0.3 atmosphere pressure 
from a distance of approximately 15 cm. so that the leaves moved as if in a 
storm. The air current, after passing the leaves, struck an inclined glass 
plate on which were placed glycerine-covered slides. The current then left 
the case through a funnel closed with cotton. On the bottom of the glass 
case two more glycerine-covered slides were placed. During experiments 
the air current was often interrupted, especially at the beginning and 
towards the end. This was done to secure the strongest possible distur- 
bances of the leaves. Each experiment lasted at least two hours. Freshly 
cut branches were used. These branches were afterward pressed and stored, 
for microscopical examination as to the presence of trichomes. Trichomes 
were found to have been left on the leaves in abundance. 
The glycerine-moistened slides were examined under high and low 
magnifications. At the end of each experiment, preparations of the dried 
leaves were made in a chloral-hydrate solution to find if hairs still remained. 
The branches used were: 
In Series i : 
1st day fresh 
2d day one day old 
3d day two days old 
In Series 2: 
1st day .fresh 
2d day. ...... .one day old 
3d day. ...... .three days old 
A. Experimental Series i (July 26-28, 1911). Herbarium specimens and 
two microscopical cross sections gave evidence of many hairs. 
I. Wednesday, July 26. The experiment lasted 11 hours. During the 
first hour the position of the branch was changed twice. A microscopical 
examination of the glycerine-moistened slides on July 27 showed the absence 
of club-shaped hairs, but the presence of needle-shaped hairs, much dust, 
and other impurities. 
II. Thursday, July 27. The branch used in the foregoing experiment 
was exposed to the blast again for two hours (from ii:i5A.M.toi:i5P.M.). 
When examined microscopically on July 28, the preparations showed that 
the dried-up branch as well as the fresh one had not given oft' club-shaped 
hairs but only needle-shaped hairs. 
