The border between the collenchyma and stem stem is poorly scratched. The pulvinus is a motor structure consisting of a rod of sclerenchyma surrounded by collenchyma. Stretchable support (without elastic snap-back) is a good way to describe what collenchyma does. The term was derived from the tissue in which the cells occur&colon; collenchyma. Collenchyma tissue is composed of elongated cells with irregularly thickened walls. The outer cortical cells often acquire irregularly thickened cell walls, and are called collenchyma cells. Parts of the strings in celery are collenchyma. Collenchyma tissue makes up things such as the resilient strands in stalks of celery. Collenchyma is absent in monocot stems, roots and leaves. Collenchyma is Greek word where "Colla" means gum and "enchyma" means infusion. Collenchyma cells are typically quite elongated, and may divide transversely to give a septate appearance.