These cells also compose the horizontal rays in wood. Parenchyma cells retain the ability to divide throughout their lives, so they are important in vegetative regeneration and wound healing. For example, roots growing from a stem cutting are created and differentiate from parenchyma cells that are scattered throughout the stem and spring into action when cued by hormonal changes that a new structure is needed. Because parenchyma tissue is composed of only one cell type, parenchyma is called a simple tissue . Like parenchyma cells, collenchyma is living at maturity.
Collenchyma cells have thick primary walls composed of cellulose .
Different biological stains are attracted to either cellulose or lignin. Because collenchyma cell walls are not lignified, the collenchyma strands are flexible, thus ideal for structural support and protection in growing shoots or flexible structures like leaves. Collenchyma is found near the surface of cortex in stems and along the veins of leaves, where it provides structural support and protection against breakage. These features make sclerenchyma tissues hard, rigid, and somewhat brittle. Different biological stains are attracted to either cellulose or lignin.