Structure of phloem tissue. (a) Microscope slide image and drawing of a sieve tube element and companion cell in transverse section (TS), (b) photomicrograph image and drawing of a sieve tube element and companion cell in longitudinal section (LS).
Structure of phloem tissue. (c) Transmission electron micrograph image and drawing of a sieve tube element and companion cell in transverse section (TS)
Phloem sieve tube elements structure & function table
Phloem companion cells structure & function table
Comparison of xylem & phloem tissue table
Understand the difference between sieve tube elements and companion cells, and how they are different to xylem tissue. Remember that mature xylem tissue is dead, so there is no evidence of organelles, and they have lignified cell walls, whereas sieve tube elements have no lignin, do have sieve plates, and their companion cells contain nuclei and dense cytoplasm.
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