Anomalous secondary growth

             SECONDARY GROWTH IN DICOT STEM

                                         BIGNONIA

    

                      Bignonia, is a member of Bignoniaceae family & it is a dicotyledonous plant. It was a woody climber. In that , young stem shows ridges & furrows.

In transverse section, bignonia shows following anatomy,such as :

   

                        

                   

EPIDERMIS: 

• It is the outermost layer of the rectangular cells .
• Thick cuticle is present over the upper layer of the epidermis.

HYPODERMIS:

• Beneath the epidermis,few layered collenchymatous  hypodermis cells are present in the ridges and furrrows.
• Chlorenchyma cells may also be present.

CORTEX:

•  A single layered cortex acts as endodermis, and also contains    inter cellular spaces. 
•  And the cells are without casparian thickenings.

PERICYCLE:

•  It is made up of  alternate bands of sclerenchyma cells with  parenchymatous tissues.    
• Pericycle is not continuous , present like patches.

VASCULAR BUNDLES:

•   Vascular bundles are arranged in the form of ring and they         are collateral,con-joint,open & with endarch xylem.
•   Secondary phloem present below the pericycle.
•   Cambium as single-layered.
•   Medullary rays made partition of sclerenchymatous patches.

ANOMALOUS SECONDARY GROWTH:

• Phloem growth is higher in rate , so the presence of medullary rays makes the phloem pulls inwards, this may makes like wedge-shaped phloem.

                             

• While the secondary phloem & secondary xylem present upside and primary phloem & secondary xylem present below then disappears as faster as faster respectively.