A new apparatus for continuous measuring the falling velocity of wind-dispersal seeds is presented in this
paper. The key unit of this apparatus is the photo-detectors installed on the ends of a vertical tube. The photodetector
is composed of a LED and a photo-sensor. The LED light goes through a horizontal slit to from a flat light
plane, which be received by the photo-sensors on the opposite side. When a plant seed falls down and passes through the
flat light plane, a pulse signal will be detected by the photo-sensor. The average falling velocity of the seed is calculated
according to the falling time and the distance from the starting point to the testing point. By using several tubes and
photo-detectors, the apparatus can continuously measure the velocity of a seed falling down to different height. This apparatus avoids the affect of the static electricity and airflow to the seeds.