Vol. 15—1961 - NorthEastern Weed Science Society

Modified
Durham Sample:­
An alternate meth~d ~f overcoming the directional bias
is the use of a square slide in a streamlined circular holder.
One of our designs allows the air to flow smo~thly over the
surface, even at high speeds, as evidenced by wind tunnel
tesYs. This sampler has two improvements over the standard
rurham sampler: equal orientation with any air flow and
:ess modification of approaching air currents. It retains
~he other advantages and disadvantages.
Cylinder
Samplers
A cylindrical surface of suitable size is a reasonably
efficient collector of particles in the pollen size range at
any but low wind speeds. As an added advantage, an equation
has been developed for describing its efficiency mathematically.
The collecting efficiency varies directly with wind speed,
particle size and particle density and inversely with cylinder
diameter. In sampling ragweed pollen on a cylinder of fixed
size, wind speed is the only variable and a curve of collection
efficiency vs. speed may be constructed. Although small
cylinders are more efficient, they tend to overload too
quickly for 24-hour samples, especially in dusty air, and some
~ompromise between efficiency and length of the sampling period
is necessary. Cylinder samplers are mounted in a vertical
p~sition on vanes to keep the sampling surface oriented into
the wind.
A cylinder large enough to ac~ept a standard glass
microscope slide in a vertical position on the leading face,
without too much alteration of the cylindrical shape, should
be 4 inches in diameter. This is too large for proper
sampling at the usual wind speeds. To retain both the standard
size slide and the smaller cylindrical shape, I-x 3-inch
slides may be made of thin (~.4 rr@.) transparent plastic
and attached t~ the side of a smaller cylinder (1 7lB-inch
diameter) in a curved position. After a 24-hour exposure,
such olastic slides will return to their original flat shape.
3torage and pollen counting are essentially the same as with
glass slides.
A cylinder sampler with 1/4- or 3lB-inch diameter has
improved efficiency at low wind speeds. This may be made ~f
transparent plastic rod (luci te or pleziglass) 'Hi th a 1/16-inch
wide flat portion f'or-med on the side facing t.h e wlnd. The
same sticky medium (we prefer silicone gre~se) as used on
the micr-os cope slides is apnLt.ed to the forv18rd face of the
cylindrical rod. The pollen remains on the r~d "ltd le b~iIjg