Differentiation and development

New cells from meristems and the cambium become specialised for particular jobs: this is differentiation. Their walls and protoplasm change. For example, a cell that becomes a tracheary element (a water-carrying xylem cell) loses its protoplasm entirely and builds very strong walls of lignin and cellulose (secondary walls), so it can carry water under great tension.

Plant cells can also go back. Living, differentiated cells can regain the power to divide: dedifferentiation. For example, ordinary parenchyma cells can turn into interfascicular cambium ("inter" means between, as in an inter-house match; this cambium forms between the vascular bundles) and into cork cambium. The new cells they produce then lose the power to divide again and mature for a specific job: redifferentiation.

Plant differentiation is open: cells from the same meristem can end up quite different, depending on where they are. Cells leaving the root apical meristem may become root-cap cells or epidermis cells, depending on their position.

Development covers all the changes in a plant's life, from germination to old age (senescence): cell division, expansion, maturation, senescence and death. In short, development = growth + differentiation.

Plants can take different forms depending on their surroundings or their stage of life: this is plasticity. One example is heterophylly, having different kinds of leaves on one plant. In cotton, coriander and larkspur, young (juvenile) leaves differ from mature ones. In the buttercup, leaves growing in water look different from those in air.