Extra-stelar secondary growth: The secondary growth that takes place as a substitute assess to protect the dermis and other tissues present beneath the epidermis from splitting due to the centrifugal strain exerted for the same of intra-stelar secondary growth is said to be extra-stelar secondary growth.
The development occurs in stellar region when cambium grows and in extra stellar region or cortical region when cork cambium starts emergent in dicot plants. During secondary growth the cambium starts growing first resulting in thickness in stellar region. After that the cork cambium increases in width.
(i) The secondary vascular tissues formed in the plant body due to intra-stelar secondary growth create centrifugal pressure.
(ii) The rate of pressure is also increased, consequently with the progress of secondary growth.
(iii) Due to this pressure epidermis may be broken down.
(iv) Moreover, an influence of this pressure may fall on hypodermis and cortex.
(v) So, to protect the plant from the harmful effect caused by the intra stelar secondary growth, secondary growth also takes place in the extra-stelar region.