Apical meristem in detailed and the kids are in simple words for a person to talk about it in the folding table and chairs for seedling 😺 to be the parents 😦😦 to be the parents genotype of the above is me and I can explain it in the folding of the above is me and I can explain it in the folding of the above is me and I can explain it in the folding of the above is me and I can explain it in the folding of protein sequencing me to do for the kids and it's a lot to say it is a branch and one 🕜🕜🕜🕜🕜🕜🕜🕜🕜🕐 5

1. Dr. Rabia Ghaffar
Assistant Professor Botany
Department of Botany
University of Education, Lahore
Apical
Meristem
Plant Anatomy
BOTN3120
Lecture 5

2. Plant Anatomy: Lecture 2(B) Meristematic Tissues 2
Outline
• Shoot Apical Meristems
• Delimitation of Apical Meristem
• Evolution of the concept of apical organization
• Vegetative Shoot Apex
• Summary

3. Shoot Apical Meristem
Group of undifferentiated cells at the
apex of shoot
Self determining, autonomous
organizing center of plant
Composed of Initials, Derivatives
Gives rise to aerial organs
Foundation of primary plant body
Retains its size and shape
LS of shoot tip of flax (Linum usitatissimum) seedling
illustrating the apical meristems and derivative primary
meristematic tissues, protoderm, ground meristem, and
procambium. Source: Esau’s Plant Anatomy, Third Edition. Chapter:5 p: 104
Protoderm
Ground
meristem
Procambium

4. Delimitation of Shoot Apical
Meristem
the apical meristem is only the part of the
shoot lying distal to the youngest leaf
primordium,
whereas the shoot apex includes the apical
meristem together with the subapical region
bearing young leaf primordia
Message

5. Source: Prepared slide by Triarch
flickr.com
a
b
c
d
e
g
f
A LS of Coleus shoot apex
a: Apical meristem
e: Shoot apex
b & c: developing
axillary buds
d: Young leaf primordia
f & g: developing leaves

6. Evolution of the concept of apical organization
Different concepts to explain: How does a Primary plant body develops by
the activity of APICAL MERISTEMS

7. Apical Cell Theory
Histogen Theory
Tunica Corpus Theory
Cytohistological Zonation
Anneau Initials Meristem
d’attente Concept
Theories explain Shoot
Apical organization

8. LS of the Shoot apical region of Equisetum with
Apical Cell Theory
Hofmeister & Nageli (1878)
Seedless Vascular Plants
Salient Features:
 Presence of a single tetrahedral apical cell in the shoot
apex of most vascular Cryptogams (Algae, Fungi,
Bryophytes & Pteridophytes)
According to this theory a single apical cell is the structural and
functional unit of apical meristem and it governs the whole
process of growth.
 Such a single apical cell occurs in algae and majority of
bryophytes and pteridophytes.
A single apical cell was also believed to be present in seed
plants.
A: Pyramidal apical cell of Equisetum B: Lenticular or three sided Apical cell of Pteridium rhizome

9. A: Shoot apex of Equisetum B: Apex of Pteridium rhizome

10. Histogen Theory
Hanstein (1870)
d: Dermatogen; pb: Periblem; Pr: Plerome
LP1, LP2: first & second leaf primordia
angiosperm
shoot apices and embryos.
2 Considerations:
The main body of the plant does not arise from a single
superficial cell but from a mass of meristematic cells
This is a massive meristem of considerable depth
comprising
of three parts, the histogens
1. the dermatogen is the precursor
of the epidermis;
2. the second, periblem gives rise to the cortex;
3. the third, plerome constitutes the inner mass of the
axis.

11. LS of the shoot apex of Solanum tuberosum
Sourse: Esau’s Plant Anatomy, Third Edition. Chapter:6 p: 142
Corpus
2-layered
Tunica
Leaf
Primordia
Tunica Corpus Theory
Schmidt (1924)
angiosperm shoot apices
Salient Features:
It states that the initial region of the apical meristem consists of
(1) the tunica:
 one or more peripheral layers of cells
 that divide in planes perpendicular to the surface of the
meristem (anticlinal divisions), and
 they undergo surface growth and maintain their
continuity over the enlarging mass below
 It arises from a small group of separate initials
(2) the corpus:
 a body of cells several layers deep
 in which the cells divide in various planes.
 Corpus adds bulk to the apical meristem by increase in
volume. Corpus has its own initials

12. Fig. 3 LS of Elodea shoot apex; representing one cell thick Tunica
layer
Fig. 5 LS of Coleus shoot tip. L1 & L2 Tunica layers L3 Initial layer of
the Corpus (C)
Tunica
Corpus
Mantle & Core concept:
Mantle includes “all layers at the summit of the apex
in which anticlinal divisions are sufficiently frequent to
result in the perpetuation of definite cell
layers”; the mantle overarches a body of cells called
the
core.
Tunica replaced by Mantle; Corpus is replaced by
Core
A modification of Tunica-Corpus concept
Popham (1951),

13. Cytohistological Zonation
Foster (1941)
Gymnosperm Shoot Apices
based on
• planes of division (anticlinal, periclinal, diagonal)
• cytologic and
• histologic differentiation
• the degree of meristematic activity of the
component
cell complexes
Rib Zone----pith
Peripheral zone----
meristematic, give
rise to LP and
procambium,
cortex
Central
Zone
Surface meristem
Apical
initial
Periclinal divisions
Periclinal + anticlinal divisions
random divisions

14. Cytohistological Zonation
Foster (1941)

15. LS of shoot apex of
Pinus sp.
Source: https://www.flickr.com/photos/plantdiversity/albums
CMZ
API
Rib
Peripheral
meristem

16. LS of shoot apex of Ginkgo biloba
Source: https://www.flickr.com/photos/67221672@N07/

17. Anneau Initial & meristeme d’attente
Buvat (1955)
Diagram illustrating the shoot apex of
Cheiranthus cheiri interpreted
according to the méristème d’attente
concept (Sourse: Esau’s Plant Anatomy, Third
Edition. Chapter 6 p: 137)
ma: meristeme d’attente
ai: anneau initial
mm: meristeme
medullaire

18. Anneau Initial & meristeme d’attente
Buvat (1955)
ma: meristeme d’attente
ai: anneau initial
mm: meristeme medullaire
proposed that
 peripheral and
 subterminal regions are real
initiating zones whereas
 distal zones are inert in nature.
1. The anneu ( the peripheral active zone)
2. The meristem d'attente ( the waiting
meristem which becomes active only during
formation of terminal flower or inflorescence)
3.The meristem medullaire ( the central pith
region)

19. Vegetative Shoot Apex

20. Various forms of Vegetative Shoot Apex
Narrow, conical--------------Gymnosperms
Broad , flat-------------------Ginkgo & Cycads
Narrow, elongated--------monocots
(grasses, Elodea) & Eudicots
Sunken--------------------Eudicots
Pit-like, depression------------Eudicots

21. Summary
THANK YOU
Source of the presentation
Ray F. Evert. Esau’s Plant anatomy : Meristems, Cells, and Tissues of
the Plant Body : Their Structure, Function, and Development. 3rd
Ed.
John Wiley & Sons, Inc. 2006. Chapter 6: Apical Meristems p. 133-
174.