THE ACTION OF WIND IN THE DISPERSAL OF SPORES FROM CUP-SHAPED PLANT STRUCTURES

Abstract

Observation of Lycopodium spores in glass vessels of various sizes and shapes subjected to winds ranging from 0.6 to 7.1 meters per second showed that spores are blown from funnel or egg-cup-shaped vessels more readily than from rectangular vessels or horizontal glass slides. Lycopodium spores were not visibly dispersed from a conical funnel with mouth 4 cm. diameter at wind speeds below 3 meters per second. Soredia of the lichen Cladonia were blown out of their funnel-shaped podetia by winds of 1.5–2 meters per second (3.3–5.3 miles per hr.) although no soredia were blown from a horizontal glass slide at the same wind speeds. When smoke flowed over conical glass funnels in a wind tunnel, two eddy systems were observed. The first took the form of twin vortices with almost vertical axes, one on either side of the median line in the funnel. Each vortex was smallest at the narrowest part of the funnel and widened upwards. The second system was a single permanent elliptical eddy with horizontal axis near the funnel mouth. The upper side of this eddy moved with the wind, the lower against it. Thus, across the median line of the funnel parallel with the air stream but in the opposite direction, there is a flow of air made up of the mingling of the bottom part of the permanent elliptical eddy and the inner edges of the two vortices. It is assumed that, in nature, the two eddy systems created by wind blowing over funnel-shaped plant structures will effectively remove spores and bodies of comparable size. The twin vortices suck spores from the bottom of the funnel and the rotation of the upper elliptical eddy raises the spores along the upwind wall of the funnel and ejects them into the wind above. In a hemispherical plant structure, a single permanent eddy carries spores backwards and up the upwind surface. This kind of dispersal could occur in a variety of plants, including Discomycetes and wind-pollinated plants.