Settling speed of corn (Zea mays) pollen

The settling speed of corn pollen is fundamental for determining the distance that corn pollen can be transported in the atmosphere and for determining its probability of being deposited on plants and the ground. The settling speed, vS, and the corresponding volume-equivalent diameter, De, of corn pollen grains were measured at various times after pollen was released from the anther. The geometric size of pollen grains decreased with increasing time after release from the anther due to loss of water during drying. The density of corn pollen ranged from 1.25 g cm−3 when freshly collected to 1.45 g cm−3 when dry. Values of vS ranged from 21 cm s−1 for pollen grains with De of 76–80 μm to 32 cm s−1 for pollen grains with De of 103–106 μm. Over a wide range of pollen sizes (76–106 μm), which included pollen collected from two hybrid varieties and one inbred line, vS was described well (P<0.000001) by theoretical values based on the size, shape, and density of the pollen and using an aerodynamic drag coefficient given by cd=24Re−1(1+0.158Re2/3).