Answer in detail.
Explain Histogen theory,

Explanation

Histogen Theory:Histogen theory is proposed by Hanstein(1868) and supported by Strassburger.The histogen theory as appilied to the root apical meristem speaks of four histogen in the meristem.They are respectively
(i)Dermatogen:It is a outermost layer.It gives rise to root epidermis.
(ii)Periblem:It is a middle layer.It gives rise to cortex.
(iii)Plerome:It is innermost layer.It gives rise to stele.
(iv)Calyptrogen:It gives rise to root cap.

Korper Kappe Theory:Korper kappe theory is proposed by Schuepp.There are two zones in root apex-Korper and Kappe.

(i)Korper zone forms the body.
(ii)Kappe zone forms the cap.This theory is equivalent to tunica corpus theory of shoot apex.The two divisions are distinguished by the type of T (also called Y divisions).Korper is characterised by inverted T divisions and kappe by straight T Divisions.
Quiescent Centre Concept:Quiescent centre concept was proposed by Clowes (1961) to explain root apical meristem activity.These centre is located between root cap and differentiating cells of the roots.The apparently inactive region of cells in root promeristem is called quiescent centre.It is the site of harmone synthesis and also the ultimate source of all meristematic cells of the meristem.