Anomalous Secondary Thickening in Bignonia

Bignonia belongs to the family Bignoniaceae.
Bignonia young stem cross section details:
1.Wavy outline with prominent ridges and furrows
2.Epidermis single layered with cuticle
3.Hypodermis is collenchymatous
4.Cortex is parenchymatous
5.Endodermis not prominent
6.Pericycle unilayered
7.Vascular Bundles are conjoint, collateral, open and arranged in a ring around pith
8.Xylem is endarch
Bignonia: Anomalous secondary thickening
Anomalous Secondary Thickening in Bignonia cross section c.s
Anomalous secondary thickening is due to the
a) Abnormal functioning of cambium.
During Secondary thickening
1.At the beginning, fascicular cambium and interfascicular cambium join to form a cambial ring. The cambium behaves normally producing more secondary xylem towards the inner side and less secondary phloem to the outside.
2.After some time, the cambium develops unidirectional areas of abnormal activity at four diagonal points. At this points, cambium produces lesser amount of secondary xylem and more amount of secondary phloem
3.This phloem masses form four deep wedges supported by transverse bands of sclerotic cells
4.Thus four wedges of secondary phloem intrudes into secondary xylem.
5.Thus 4 wedges of secondary phloem and 4 ridges of secondary xylem are formed.
6.Periderm formation is normal as activity of cork cambium is normal
See notes on Anomalous Secondary thickening in Dracaena
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