Advanced Plant AnatomySecond Year Biology

Dr Emad A.M. FarahatBotany and Microbiology Department

Date Lab. No. Contents in brief

1 Course description and introduction to plant anatomy Theories of structural development (Stem and Root)

7/10 2 Periderm (structure and types), Bark, lenticels and leaf

abcissions, wood cork

14/10 3 Stelar system Anatomy of the node

21/10 4 Permanent primary tissues Vascular cambium activities Common forms of 2ry thickening in Dicots &Gymn.

28/10 5 Secondary V. tissues in Dicots and Gymn. Species

4/11 6 Dendrochronology (sap wood, heart wood, grain and knot in

wood) 2ry thickening growth in Monocots.

11/11 7 More about Dendrochronology

18/11 8 Anomalous 2ry growth in Dicots and Gymn (stem and root)

25/11 9 Plant structural adaptation

2/12 10 Exam and free reading related articles and activities

9/12 11 free reading related articles and activities

16, 23/12 12 Comments on free reading articles and related activities Revision

Syllabus of Theoretical Plant Anatomy 2008/09Supervisor: Dr Emad Farahat Year: Second year biology, Faculty of Science - كلية بيولوجي الثانية الفرقة العلوم

Theories of structural development and differentiation

Regions of meristematic cells are distinguished according to:

No. and position of initiating cellsThe planes of division and consequent

arrangement of cellsThe size, shape and content of cellsThe rate of maturation of cells

The theories dealing with the methods of origin of these zones are:

1) The Apical Cell Theory2) The Histogen Theory3) The Tunica-corpus Theory

Theories of structural development and differentiation

1-The Apical Cell Theory

• It states that “ the seed plants possess a single apical cell which produces by its activity the whole of the plant body”

Criticism: many Angiosperms and Gymnosperms have several apical initial cell, which give rise to the plant body….i.e. this theory is not applicable to seed plants

2- Histogen Theory

• This theory proposed that the seed plants have growing regions or points (apical meristem)

• All the meristematic cells are all alike and constitute promeristem

• The cells of promeristem are differentiated into 3 regions: Dermatogen, periblem (ground promeristem) and plerome (procambium)….=== histogn= tissue builder

1. Dermatogen: single outermost layer in the stem gives rise to Epidermis. In Roots: it is also single layer giving rise to calyptrogen Root Cap.

2. Periblem (Ground promeristem): it is internal to the dermatogen. It is a single layer at the apex and multilayered in central part…gives rise into Cortex.

3. Plerome (Procamium) : it is the central meristematic region of the apex, composed of isodiametric cells. It differentiate into the stele (Vascular tissues, ground meristem, ray parenchyma etc). Roots are the same

The Tunica-Corpus Theory

• Only applied for shoot apices• According to it there is Tunica consists of 1 or more

layers of cells …and Corpus, a mass of cells enclosed by the Tunica

• The 2 regions are differentiating from each other by different rates and methods of growth and division• Tunica cells show anticlinal divisions i.e. SURFACE GROWTH…..while Corpus cells divide into anticlinal and periclinal planes…..i.e. in all directions

The Tunica-Corpus Theory

Each Tunica layer

arises from

Group of separate initial

layers…one layer initial for corpus

Corpus single initial layer

Divide periclinally to give rise to Derivatives

Derivatives divide in all

planes ..resulting in inner mass of

cells

The number of initials varies from one to many as follows

The Tunica-Corpus Theory

A- initial solitary with oblique anticlinal division only

Position and planes of divisions of stem apex initials

B- initials many, superficial with their divisions both anticlinal and preclinal

The Tunica-Corpus Theory

Position and planes of divisions of stem apex initials

C- initials several, superficial with their divisions both anticlinal and preclinal

The Tunica-Corpus Theory

Position and planes of divisions of stem apex initials

D- initials in three tires , 2 outer with division anticlinal only formed 2 layered Tunica. the inner layer with preclinal division forming Corpus.

The Tunica-Corpus Theory

Position and planes of divisions of stem apex initials

A, B and C, there are no distinct Tunica and Corpus; while in D the vice is.

• It is simple in structure than shoot apex• Root cap is formed by the same initials as

those that build the root proper except in Moncots

• Growth in root cap and root apex is in opposite direction

• It consists from 4 histogens (dermatogen, perilem, plerom and calyptrogen)

Root Apex

Lower Vascular plants: have only one apical cell, which gives rise to the whole root…….cap is distinct but have the same origin

Root Apex

In Many Gymnosperms (B): there are TWO sets of initials: the inner forms plerome, the outer form periblem and cap…….cap is indistinct and independent

Root Apex

In angyosperms ..dicots and monocots: there are THREE (rarely four) groups of initials.

In Dicots (C): distal group forms cap +

DermatogenMedian group forms periblemInner most forms plerom

Cap is indistinct and independent

Root Apex

In Monocots (D): distal group forms cap

onlyMedian group forms

Dermatogen + periblemInner most forms plerom

Cap is distinct structurally and independent

Root Apex