SummaryEvolutionary proposals involving pollen grain characters have treated germinal apertures as though they were formed by one universal process and hence derivable from a common type. A review of published data on apertural formation for pollen ofSilene, Tradescantia, andNelumboand original information forEpilobiumindicates that there are several possibly distinct apertural induction processes. It would seem to be an oversimplification and perhaps misleading to ignore apertural genesis in interpretations involving relationships between taxa.