Elongated support cells with unevenly thickened walls that remain alive at maturity are which type?

1. The clue is the uneven wall thickening combined with being alive at maturity. 2. Collenchyma cells are elongated with unevenly thickened walls, are alive at maturity, and usually sit just below the epidermis. 3. They support the stem and leaves, and the strings of a celery stalk are an everyday example. 4. Sclerenchyma also supports the plant but many of its cells are dead at maturity and their walls are lignified. 5. Tracheids are dead water conducting cells and sieve-tube cells conduct sugars, so neither is a support cell of this kind. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 30 "Plant Form and Physiology", section 30.2 Stems_