Side wall between differentiating vessel members. Secondary wall deposition not yet evident. In the older cell (below), microtubules concentrate near young helical thickenings and are absent along the primary wall.
Side wall between vessel members with differentiating helical thickenings. More mature cell (right) indicated by larger amount of secondary wall deposition. Vesicles between plasmalemma and secondary wall are evident.
Wall between older (right) and younger (left) vessel members. Microtubules accumulate near the secondary wall in younger cell. Membrane-bound vesicles appear as blebs on plasmalemma. Primary wall of older cell are partly hydrolyzed.