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What is the difference in base division of corpus and cap ?

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Tunica Corpus Theory:
This theory was proposed by Schmidt (1924) According to this theory, the shoot apex consists of two distinct zones-

(i) The outer tunica, which surrounds and envelops:
Tunica consists of one or more peripheral or outer layer of cells. These cells are comparatively smaller and divide by anticlinal divisions i.e.with the axis of mitotic spindleparalled to the surface. Thus the cross walls separating the two daughter cells are formed perpendicular to the surface so that the number of layers do not increase. Cells derived from tunica differentiate into epidermis

(ii) The inner corpus. which forms the central core:
The corpus occupies the central portion in which the cells arc comparatively larger. These cells divide in all the planes. These cell form the procambium and ground meristem. Procambium gives risc to pr mary xylem, primary phloem and intrafascicular cambium. The ground men stem forms the ground tissue (i.e. cortex, endodermis, penicycle and pith).

(B) Root Apex :
A group of initial cells, present at the subterminal region of the growing root tip, which is protected by a root cap is called root apical meristem or root apex.

  1. It is embryonic in origin and formed from the radicle part of embryo.
  2. In adventitious roots it is produced from derivatives of root appex.
  3. The root apex is short as compared to shoot apex. It is more or less uniform due to complete absence of lateral.
  4. Appendages (leaves and branches) and differentiation of nodes and intemodes.
  5. Cell division in the apical meristem adds new cells both to the body of the root and to the root cap.
  6. Histogen theory of Hanstein (1870), the root apex of most of the dicotyledons consists of three meristematic zones or layers –
    • Plerome forms pith, vascular strands and pericycle,
    • Periblem forms endodermis and cortex and
    • Dermatocalyptrogen gives rise to protoderm as well as the root cap.
  7. The theory believes that in monocotyledons, the root cap is derived from a separate layer of initials called calyptrogen and the protoderm is derived from dermatogen.

Periblem is derived from dermatogen.

8. In addition to actively dividing cells, a zone of inactive cells is present in the central part of the root apex called quiescent centre (clowes, 1961). It is a central cap- like or hemispherical region of inactive cells present in between the root cap and the active meristematic region of root apex. This zone contains several hundred cells which are characterized by having lower concentration of DNA, RNA and protein. These cells also contain fewer number of mitochondria, less endoplasmic reticulum and small dictyosomes.

9. The quiescent centre acts as reservoir of cells and becomes active whenever the initials get damaged or during the establishment of the secondary’roots. However, normally the cells of quiscent centre do not divide and remain inactive.

10. Mainly in roots with a very regular arrangement of cells in the apical meristem, such as of Zea mays, it is possible to conclude form the study of cell lineages that there is a central region of cells which divide rarely or not at all. The cells on the periphery of this hemispherical or cup – shaped region are meristematic. This inactive or passive region of cells is known as ‘quiescent centre’.

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