Sclerenchyma Cells Sclerenchyma cells function in support. They have very rigid, thick secondary walls strengthened by lignin . Water-Conducting Cells Xylem consists of two cell types, both with secondary walls and both dead at functional maturity. Water flows from cell to cell through pits. Also function in support.
Vessel elements are wider, shorter, thinner-walled, and less tapered than tracheids.
Vessel elements are aligned end to end. The end walls are perforated, permitting the free flow of water through long chains of vessel elements called xylem vessels. The cells are alive at functional maturity. Protoplasts lack a nucleus, ribosomes and a distinct vacuole. In angiosperms, the end walls of sieve-tube members have pores and are called sieve plates .