Fig.
7.5-5b.
Transverse section of a vascular bundle of sedge (Scirpus). As in Fig.
7.5-5a, this vascular bundle has a large hole (at X)
caused by a protoxylem vessel element being torn apart by the
continued growth of surrounding cells. The large vessels (marked with V) did not
mature until this region of internode had stopped elongating: because the
surrounding cells are not expanding, they are not pulling on these dead vessel
elements so there is no tendency for them to be torn apart – that happens only
to the very first, smallest protoxylem tracheary elements, and usually just in
internodes that elongate a great deal.