Helical thickenings were observed on the vessel walls of ninety woods indigenous to New Zealand. They were not observed in a further eighty-eight species. Four types of thickenings are described: faint striations, light helical thickenings sometimes merging with the vessel wall, prominent helical thickenings and very prominent close helical thickenings. These types are illustrated with scanning electron micrographs.
Although the helical winding orientation was predominantly in the S-direction, considerable variation was observed in the helical winding angle both between adjacent vessel members of similar dimensions, and also within individual cells.
Vestures were observed adhering to the helical thickenings in three species.