Companion cellA small living cell beside a sieve tube element. It keeps that element alive, because the element has no nucleus of its own.
Sieve tube elementA living cell with no nucleus. Sieve tube elements joined end to end form a sieve tube, which carries sugars made in the leaves.
Sieve plateThe end wall between two sieve tube elements. Its pores link the contents of one cell with the next.
Companion cell nucleusThe large nucleus of a companion cell. A mature sieve tube element has lost its own.
Phloem parenchymaLiving, box-shaped cells of the phloem. Food is stored in them.
Xylem 6
Vessel elementA wide, dead, hollow cell of the xylem. Vessel elements joined end to end form a vessel, a pipe that carries water.
TracheidA long, narrow water-carrying cell with tapering ends. The ends are closed, so water passes to the next cell through pits.
PitA thin place in the wall. Water moves cell to cell through pits.
Perforation plateThe open end wall between two vessel elements. Water passes straight through it.
Lignified wallA thick wall hardened with lignin. It is left standing after the living contents of the cell have gone.
Xylem parenchymaThe living cells of the xylem. Vessel elements and tracheids are dead when they carry water; these cells stay alive.
How this list was compiled: Every name was checked on 2026-10-01 in at least two places, for facts only and with nothing copied. (1) University of Vigo, Atlas of Plant and Animal Histology: Plant tissues, Vascular (xylem and phloem), https://mmegias.webs.uvigo.es/02-english/1-vegetal/guiada_v_conductores.php. (2) Wikipedia, text only: Xylem, Phloem, Vessel element, Tracheid and Sieve tube element, https://en.wikipedia.org/wiki/Xylem, https://en.wikipedia.org/wiki/Phloem, https://en.wikipedia.org/wiki/Vessel_element, https://en.wikipedia.org/wiki/Tracheid, https://en.wikipedia.org/wiki/Sieve_tube_element. (3) W. C. Stevens, Plant Anatomy (1907), the chapter on the primary vascular bundle, https://archive.org/details/plantanatomyfro00stev (public domain). (4) J. N. Martin, Botany for Agricultural Students (1919), the section on conductive tissues, https://archive.org/details/botanyforagricul00mart (public domain). Licence: own work
The drawing: Drawn for this site on 2026-10-01 from plain geometry; nothing traced. Licence: own work
How it works
This companion cells diagram opens on the phloem: a sieve tube with its sieve plates, and a companion cell beside each element. The second view is the xylem: a vessel and two tracheids. Tap a name, or press Quiz me.
Read the full guide
Phloem: living cells that carry sugars
A sieve tube is a row of sieve tube elements joined end to end, with a sieve plate at each join. A mature element has no nucleus, so a companion cell with a large nucleus lies beside it and keeps it alive.
Xylem: dead, hollow cells that carry water
Vessel elements are wide and open into one another through perforation plates, so they form a pipe. Tracheids are narrow, with closed tapering ends, and water moves between them through pits. Both have thick lignified walls.
Print blank turns the drawing into a label xylem and phloem worksheet.
Questions and answers
What do companion cells do?
A companion cell keeps the sieve tube element beside it alive. That element has no nucleus, so the companion cell, which has one, does the work the element cannot do for itself.
What is the difference between xylem and phloem?
Xylem carries water and dissolved minerals up from the roots, in dead, hollow cells with lignified walls. Phloem carries sugars made in the leaves, in living cells with thin walls.
What is the difference between a tracheid and a vessel element?
A vessel element is wide and open at both ends, through perforation plates. A tracheid is narrower, has closed tapering ends, and passes water on only through pits.
Do sieve tube elements have a nucleus?
No. A mature sieve tube element is alive but has lost its nucleus. The companion cell beside it has a large one.
Are xylem cells alive?
The cells that carry water are not: vessel elements and tracheids are dead and hollow when they work. The parenchyma cells of the xylem are alive.