Collenchyma cells in vascular plants support growing parts due to flexible cellulosic walls, which lignify once growth has ceased.

References

“In addition to the ‘mechanical’ cells – fibres and lignified parenchyma – a third cell type has mechanical functions. This is collenchyma. Collenchyma cells have walls which during their development and extension are mainly cellulosic. They grow with the surrounding tissue as it expands or lengthens. They are more flexible than fibres, and if they remain unlignified, as they might in association with leaf veins or midribs, or in leaf stalks (petioles), they allow for a high degree of flexibility in the organ itself. Often, after growth in length of stems has occurred, and more mechanical rigidity is an advantage, we find that the collenchyma cells become lignified, and function more as fibres.” (Cutler 2005:105)

Book section
Design in plantsIn: Nature and Design. Collins, MW; Atherton, MA; Bryant, JA, editors. pp. 95-124. WIT Press.January 1, 2005
Cutler DF

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“It is the main supporting tissue of growing organs with walls thickening during and after elongation. In older organs, collenchyma may become more rigid due to changes in cell wall composition or may undergo sclerification through lignification of newly deposited cell wall material.” (Leroux 2012:1083)

“Flexibility of collenchymatous tissues is an advantage for any plant part that is subjected to mechanical stress that would result in damaging its tissues.” (Leroux 2012:1095)

Journal article
Collenchyma: a versatile mechanical tissue with dynamic cell wallsAnnals of BotanyAugust 29, 2012
Leroux O

Living System/s

Organism
PlantsPlantaeKingdom