Association of parenchyma with secondary xylem
apo-or paratracheal parenchyma?
Secondary xylem is invariably associated with parenchymatic elements (paratracheal). In many woody species, large, very distinct large-diameter xylem vessels are interspersed with smaller tracheary elements. This type of wood is called ring porous wood.
Diffuse porous wood contains vessels, tracheids fibres and parenchymatic elements that are more or less the same diameter.
The diagrams to the right, illustrate three paratracheal parenchyma associations;
Top = aliform where the parenchyma surrounds the vessel group;
Middle = Aliform-confluent where parenchyma surrounds the vessel group, and forms distinct connecting bands, and
Bottom = confluent, where the bands are broad, and coalesce on occasion.
In contrast, apotracheal parenchyma is not associated with vessels in wood.