13. What are the cell types
that form the xylem? What are
the main features of those
cells?

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The main cells of xylem are the
tracheids the vessel elements
(these in angiosperms). The
tracheids the vessel elements are
cells that have lost cytoplasm
and only their wall impregnated with
lignin ( impermeable biopolymer)
remained. The form tubes that
communicate neighboring tubes
through pores; vessel elements do
not pores but instead they
with the successive vessel
through perforations in their
.