Presence of the protruding oncus is affected by anther dehiscence and acetolysis technique

A protruding oncus is a projection of the intine in the aperture region. The ubiquitous use of acetolysis in palynological research has led to the presence of a protruding oncus being underreported. Controlled experiments with pollen samples collected from undehisced and dehisced anthers demonstrate that the presence of a protruding oncus is affected by the state of the anther at maturity: dehisced or undehisced and by the preparation technique. In investigating the occurrence of onci, particular attention should be paid both to the dehiscence state of the anthers and the effect of the preparation technique on the intine. Although it has been suggested that protruding onci and pollen buds can be distinguished based on three criteria (size, presence of a large vacuole, separation of the protrusion from the grain), most of these distinctions break down when information is included from more recent studies. Additional study of protruding intinous structures may help clarifing the difference between pollen buds and protruding onci.