AN INTERPRETATION OF THE HYDRODYNAMICS OF POLLEN

Abstract

The pollen grains of angiosperms are usually desiccated to some extent at the time of dispersal. Rehydration is an essential prelude to germination, and this takes place by uptake of water from the stigma after capture, water entering from the cells of the stigma surface following a water potential gradient. The passage of water into the pollen grain is regulated by the cuticle of the stigma papilla in the vicinity of the contact face, and also by the apertural mechanisms of the pollen grain exine, which act by varying the degree of exposure of the underlying pectocellulosic intine according to the degree of hydration of the grain. The sequence of events during rehydration suggests that at first the vegetative cell of the male gametophyte is without a normal plasmalemma, so that the initial dilation of the grain is followed by an interval of exudation. Thereafter, with the re‐establishment of the cell membranes, the vegetative cell behaves in the manner of a normal plant cell through the period of germination.