Vessel Elements

Abstract

Vessel elements (vessel members, vessel segments of some authors) may be defined as xylem cells in which one or more pitlike structures lack a pit membrane at maturity, thus forming perforations. Perforations most frequently occur on end walls (“overlap areas”); the end walls thus are perforation plates. Vessel elements are regarded as specializations of tracheids in which loss of pit membranes on some of the end wall pits has occurred. Exceptions to the definition offered may easily be found, because evolution does not typically provide mutually exclusive categories. Absence of pit membranes may be partial in perforations in primitive vessel elements, as detailed below, and tracheary elements transitional between vessel elements and tracheids will be demonstrated more frequently as work with scanning electron microscopy progresses. Perforations may occur on apparently lateral faces of vessel elements in the case of fibriform vessel elements; this is not so much an exception with regard to location of the perforation plate as it is an example of an ill-defined end wall.KeywordsPerforation PlateTracheary ElementVessel ElementEarlywood VesselVessel Element LengthThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.