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Cork Cambium

Phellogen cuts off cells on both sides. The outer cells differentiate into cork or phellem, while the inner cells differentiate into secondary cortex or phelloderm.

Phellogen, phellem, and phelloderm are collectively known as periderm

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#XL - R Botany

Secondary Growth in Roots

In the dicot root, the vascular cambium is completely secondary in origin.

It originates from the tissue located just below the phloem bundles, a portion of pericycle tissue

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Anomalous secondary growth

Several dicotyledons show secondary growth that is different from normal  secondary growth. The deviating methods of secondary thickening are called  abnormal or anomalous secondary growth. 

e.g., Bougainvillea (Dicot)

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#XL - R Botany

Dicot stem anomalous secondary growth occurs due to following reasons:

Anomalous position of cambium 

e.g.,Serjania sp. and Bauhinia sp.

Abnormal behavior of normal cambium

e.g., Bignonia, Aristolochia, Tinospora, Clematis etc.

Extrastelar cambium formation

e.g., Amaranthus sp. 

Interxylary phloem or included phloem

e.g., Entada sp (box bean), Combretum sp (Combretum), Strychnos sp.