The cross section
illustrated here, shows part of a Bignonia stem, which
is undergoing secondary growth.
The stem is markedly angular, and
mechanical support tissues are found, particularly
collenchyma, beneath these angles. The outer cortex
is photosynthetic, with two to three layers of
chlorenchymatous cells visible. The external phloem
(EP) is capped by sclerenchymatous fibres (S).
The secondary xylem
has formed a continuous ring, and this contains some
conspicuous large-diameter vessels (2X).
The primary xylem (PX) contains some
parenchymatic elements and internal phloem (IP)
which forms part of inverted medullary vascular
bundles in this species. The pith is parenchymatous.
This stem is classified as being