Variation in structure of lateral walls of pitted elements

A diagrammatic representation of the ends of tracheids (A, B) and vessel members (C, D) in secondary xylem. Tracheids are complete cells and the communication between adjacent ones in a vertical column occurs through overlapping bordered pits in lateral cell walls. On the other hand, vessel members have perforated end walls, and the communication between cells in a vertical column occurs through perforation plates.

Lateral cell walls of pitted tracheary elements in different plants vary with respect to the structure and distribution of pits and the sculpture of the inner wall surface. In pine, tracheids have circular bordered pit apertures, whereas in oak they are slit-like. In magnolia intervessel bordered pitting is scalariform, while it is small and circular in basswood. There are half-bordered pits (shown in black) of various size and shape in the common wall with ray cells. In basswood, helical thickenings are seen on the inner surface of the secondary wall.

A = pine; B = oak; C = magnolia; D = basswood