Detail of an inverted medullary bundle in Campsis
The Bignoniaceae are known to exhibit several anomalies in their stem and root structure. Amongst these, the formation of a row of inverted medullary vascular bundles at the margin of the pith are common in a number of species in this family. The illustration to the left, shows a detail of one such inverted vascular bundle, which occurs just beneath the protoxylem (PX) of the normal vascular development in this stem. This inverted bundle is associated with a cambial zone (CZ) which has started to produce some secondary vascular tissue. Note the file of sieve tubes (S) to the inside of the internal vascular cambium.