Bordered pit pairs control movement of water from one tracheary element to the next in the wood of vascular plants (Zimmermann, 1983; Pittermann et al.
Recently, a number of species in various genera of the angiosperms have been observed to have bordered pit pairs possessing an impermeable torus as well as a surrounding margo with openings the size of the pit membrane of typical angiosperms rather than the larger openings of the margos of gymnosperms.
Many studies have shown that the increased permeability occurring during water storage of logs is a result of the decomposition of bordered pit
membranes, ray parenchyma cells, and resin canals by bacterial action (Knuth and MeCoy 1962, MacPeak 1963, Greaves 1969).
Torus-bearing intervascular pit membranes are part of the bordered pit pairs connecting tracheary elements in roots of Osmanthus armatus and Osmanthus americanus.
Bordered pit pairs connect water-conducting tracheary elements of vascular plants and allow water transport from one element to the next.
Frequently, the pit membrane is aspirated and the torus blocks one of the apertures of a given bordered pit
pair (compare Figs.
Thus, bordered pit
pairs provide passageways for water moving from cell to cell.
1), and it is the pits between tracheary elements (the so-called bordered pit
Nodal tracheary elements are isodiametric to fusiform in shape, and have crowded circular (mostly) to elongate prominently bordered pits
and uniformly thick secondary walls.
are circular to hexagonal (11 [micro]m) with circular to slit-like, crossed apertures (4-5 [micro]m).
Within the "paleoherb" families, the Saururaceae and Aristolochiaceae are polymorphic for this character, and the phylogenetic context provided by these cladograms implies that the distinctly bordered pits
in some Saururaceae and Aristolochiaceae represent reversals.
Pitted (post-expansion) tracheary elements with bordered pits
would provide enhanced support by increasing the amount of secondary wall surface (Carlquist 2012).