This document summarizes several theories of root apex organization and the concept of the quiescent centre. It discusses Nageli's apical cell theory, Hanstein's histogen theory, and Schuepp's Korper-Kappe theory, noting that each fails to fully explain root apex organization in angiosperms. The document also describes Clowes' discovery of the quiescent centre, a region of slow or non-dividing cells in the root apex meristem that is capable of resuming growth if surrounding tissue is damaged.

2. Name
Muhammad Adnan
Roll No
BBOF18BM010
Submitted To
Ma’am Rabia Saba
Subject
Plant Anatomy
Topic
Root apex organization
BS-BOT(6th)
University of Sargodha Sub campus Bhakker

3. CONTENT
 Root apex
 Theories of root apex
 Apical cell theory
 Histogen theory
 Korper-kappe theory
 Concept of quiescent centre

4. Root apex
 “All primary tissues of the plant body are derived either
from root apical meristem . This may show variation in their
Organisation.”
 during the later stages of development of embryo the cells
at the root pole become arranged in a pattern characteristic
of the species .
 This group of cells comprises the apical meristem of the
primary root .

6. Root apex organization
Several theories have been proposed to describe the root
apex organization .
1. Apical cell Theory
2. Histogen Theory
3. Korper-Kappe Theory

7. Apical cell theory
 Nageli (1958) proposed that a single tetrahedral apical cell in
the root apices brings about growth. It fas three cutting faces
for giving rise to the tissues of the body of the root. The root
cap is derived from its base. Such a proposition was not
found true to angiosperms.
 However, different types of root apices have been found in
angiosperms.

8. Histogen theory
 Hanstein (1868) put forth histogen theory proposing that in
root apex regions, three distinct histogens are found. The
dermatogen that gives rise to epidermis, the periblem to the
cortex and the plerome to’ the vascular cylinder.
 Haberlandt (1914) proposed the terms protoderm, ground
meristem and procambium, respectively for these histogens.

10. Korper – Kappe Theory
 Schuepp (1917) proposed that the cells at the root apex
divide in two planes.
 The zone with inverted ‘T’ type of division was referred to as
Kérper(cap)
 whereas other with straight ‘T as Kappe (body). The theory
basically recalls the tunica ,corpus concept of shoot apex and
Similarly, it also faiis to explain the differences in behaviour in
different species,

12. Concept of quiescent centre
 Quiescent centre A region in the apical meristem of a root
were cell division proceeds very slowly or not at all , but the
cells are capable of resuming meristematic activity should
tissue surrounding them be damaged .
 Clowes in his autoradiographic studies of DNA synthesis in
the root tip of Zea Mays , Noted a central cup-like region .

14.  The cells of which had fewer mitochondria and ER ,very small
nuclei and low rate of DNA and protein synthesis .
 He referred this inactive region as quiescent centre .
 Since than such regions have been observed in many plants .
 It consists of about 500 cells in Zea mays, 600 in sinapsis .