Publications

The North American Platanthera aquilonis Sheviak has long been known to autopollinate. Pollinia rotate forward and downward out of
the anther sacs and contact the stigma. Previous experimental evidence has indicated that this movement is effected by gravity. In addition to the move ment of whole pollinia, flowers are often found in which continuous streams of pollen massulae emanate from anther sacs and seemingly pour down onto the stigma. Experiments with cultivated plants have shown that water droplets
can collect in the centers of flowers of this species. These sometimes draw a sheet of massulae out of an anther sac either onto the surface of the droplet or into its interior. As the droplet evaporates, the massulae are deposited as a continuous layer from the anther sac onto the stigma. It is suggested that in nature dew may function to produce the observed pollen streams.