in Lincoln: Dr. F. C. Lowell. This was first located on 
Blue Hill (Milton), but because of technical problems, 
it was moved to Lincoln on May 5. We gratefully 
acknowledge the assistance of those who manned the 
various stations and Mr. Morgan’s willingness to allow 
us to place a gravitational and an automatic rotoslide 
sampler on the premises of Drumlin Farm in Lincoln. 
We are also indebted to Dr. John Noxon and the staff 
of the Blue Hill Observatory for their helpful assistance. 
Conventional gravitational samplers approved by the 
Pollen Committee of the American Academy of Allergy 
were used in all the stations. These consist of two paral- 
lel planes 9 inches in diameter, 3 inches apart and held 
with three struts. One inch above the center of the lower 
plane there is a slide holder into which the slide fits 
firmly. he supporting rod of the apparatus, 80 inches 
long, rises from a tripod base (1). We used wood instead 
of steel in the construction of the samplers. Regular 
microscope slides impregnated with silicon grease were 
employed. With occasional exceptions, slides were 
changed daily between 7 and 9 a.m. 
In two stations, Cambridge and Lincoln, we used the 
Intermittent Rotoslide sampler’ developed by Dr. 
Kugene Ogden. ‘“This sampler is designed to take pol- 
len sampler representative of the average pollen concen- 
tration over a 24-hour period by automatically operating 
periodically for short periods of time. Pollen is collected 
on the edges of two microscope slides inserted in metal 
holders which are rotated by a small electric motor. The 
leading edge of each slide protrudes from its holder and 
is oriented so its face is always at right angles to the 
direction of motion. The timing mechanism is designed 
to take a one minute sample in every twelve minutes, 
giving a total sampling time of two hours in every 24. 
*'Two samplers were kindly supplied by Dr. Ogden. 
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