Vol. 15—1961 - NorthEastern Weed Science Society

467.
equipped ~~ch of our saopl~rs with ; ho~d to aut~matically
~XPOS8 the rod while rat~ting ~nd cover it while idle. As
with ~ll pollen s~mnI2rs, it requires ~ r~in shield for
cpe r-vt.t on- in wet weather. The co st of such a. machine is
moder~t3 ~nd tho conversion of dat.a to 3 volumetric basis
should be accept~bly accurate. It requires electric power.
:2 rotorod units can be assembled with a st~,-timer to·t~ke
24
for ona-hour samples each
2n hour ~nd counterclockwise
day. Epch rotorod ~otates clockwise
for another hour, thus
~oll~cting s~mples on nIl four faces. Our latest model has
thD units on c continuous belt which exposes only one rotorod
~t'1 time.
A slight modificRtion of the rotorod sampler by
experimenters ~t the University of Michigan is called the rot~bcr
samp.Ler-, (HArrington, Gill and Warr 1959). We are new
exp2rimenting with D modified version, the rotoslide sampler,
t.ak i.ng the samples on the edge·.,of removable rni.cr-os cope slides
th~t Rre counted RS ~re those of the slide-edge-cylinder.
Volumetric
Samplers
Several devices are available for sampling measured air
which may be drAwn into the s3mpler by some me~ns, such as a
v~~uum pump. Tests may indicate high efficiency in catching
tha pollen thAt enters the machine but we cannot assume thqt
the sample gives Bn accurAte indic~tion of the pollen
concentration in the outside air. Unless the intake
opening is continuously eriented into the wind and the air
flow through the sampler is equ~l at all times to the wind
sneed in the free air approaching the intake, the system is
subject to the serious errors of ~nisokinetic sctmpling.
Sampl~rs dr~wing air through nn aperture are not recommended
for conditions of variable wind speeds unless the diameter
of the p~rticles is under 5 microns. Ragweed pcllen is
approxim~tely 20 microns.
Samplers employing molecular membrane filters have the
qdvantage of retaining pollen on tho filter surface where
it may be viewed under a microscope hut tho he~vy poll~n grnins
may not feithfully foll ...w the air stream as its vei,Btcity is
modifiad upon ~ppro~ching the filter. The number of gr?ins
T)·3r unit volume of mensur-cd af.r- may be aeve r aL times more or
icss thnn the ~ctu~l number in the same volume of outside air.
A timer m~kes possible the automatic taking of successive
filter samples (Raynor 1957).
Several recently designed devices indicate the variation
in pollen concentration during thG day. The Hirst Spore Trap
(Hirst 1952) draws measured air through an orifice oriented
into the wind. The pollen is impacted on a microseope