ANATOMY - lecture-notes.tiu.edu.iq

ANATOMY

ANATOMY AND

MORPHOLOGY OF STEM

(PRIMARY)

ANATOMY OF STEM

(Primary)

Learning outcomes

Explain stem and bud parts, types,

and structural types

Explain the epidermis, ground tissue,

and vascular tissues in stem

STEM

MORPHOLOGY

3

MORPHOLOGY-STEM

AND BUDS

1. STEM

a. Stem Parts

i. Twig Surface Parts

Bud- an immature shoot.

Internode- a section or region of

stem between nodes.

Leaf scar - a mark indicating

former place of attachment of

petiole or leaf base.

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MORPHOLOGY-STEM

Lenticel- a pore in the bark, as

breathing pores for gas exchange.

Node- region of stem from which

a leaf, leaves, or branches arise.

Prickle- a sharp-pointed out-

growth from the epidermis or

cortex of any organ.

Stipular scar - a mark indicating

former place of attachment of

stipule.

6

MORPHOLOGY-STEM

7

MORPHOLOGY-STEM

Terminal bud scale scar rings -

several marks in a ring indicating

former places of attachment of

bud scales.

Vascular bundle or trace scar -

a mark indicating former place of

attachment within the leaf scar of

the vascular bundle or trace.

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MORPHOLOGY - STEM

Bark –tissues of plant outside

wood or xylem.

Pith – centermost tissue of stem,

usually soft. Not always visible

in older wood.

Wood – xylem consisting of vessels

and /or tracheids, fibers and

parenchyma cells.

ii. Major stem parts

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MORPHOLOGY-STEM

Stem Types

(Classification based on

direction of growth

10

11

Arborescent – treelike in

appearance and size.

12

Climbing- growing upward by

means of tendrils, petioles or

adventitious root.

13

Decumbent – reclining or lying

on the ground with tips

ascending.

ANATOMY OF STEM (Primary)

⚫ Introduction

⚫ The stem, the part of the primary body, derived from the shoot apical meristem.

⚫ Meristems form the new cells of a plant and the apical meristem occur at the tip of the shoot and provides primary growth.


⚫ The shoot meristem produces the cells that will form the major tissues of new stem and leaf:

⚫ i. Protoderm, epidermal cells that are still meristematic and in the early stages of differentiation.

⚫ ii. Ground meristem, young cells of pith and cortex.

⚫ iii. Provascular tissues, young cells of xylem and phloem. Fig. 1 and 2.


Fig. 1

Apical meristem

of shoot.


Fig. 2.

Stem near

meristem

1.& 2.Ground

meristem

3.Provascular

4.Protoderm


⚫ Epidermis

⚫ Outermost surface, a layer of epidermal cell.

⚫ Prevent the lost of water, barrier against invasion by bacteria, fungi, and small insects.

⚫ Outer wall with cutin (fatty substance, impermeable to water), become a layer, cuticle.

⚫ A layer of wax may be present outside the cuticle. Fig. 3.


Fig. 3.

Epidermis with

cuticle.


⚫ Ground Tissue

⚫ Interior to the epidermis, simple or

complex.

⚫ Photosynthetic parenchyma and

sometimes collenchyma in simple cortex.

⚫ Complex cortex, presence of laticifers,

resin duct, calcium oxalate.

⚫ Fig. 4 to 7.


Fig. 4

Helianthus,

Eudicot.

(sunflower)

Fig. 5. Zea mays. Monocot (corn)

Ground tissue


Fig. 6. Laticifer,

Nerium oleander.

Fig. 7. Calcium oxalate,

Mangifera indica (Mango)

Ground tissue


⚫ Vascular Tissues

⚫ Two types: Xylem and Phloem.

⚫ Xylem: Tracheary elements plus some parenchyma and sometimes sclerenc-hyma.

⚫ Two types of tracheary elements:

⚫ Tracheids and vessel members.

⚫ Fig. 8 to 10.


Fig. 8

Tracheary

element with

secondary wall.

1. Parenchyma

2. Annular

3. Scalariform

4. Reticulate

5. Pitted


Fig. 9. Tracheary element in the stem

of Mangifera indica (mango) x 1,500.

Reticulate

Annular


Fig. 10. Tracheary element in the stem of

Mangifera indica (mango) x 5,000

Pitted


⚫ Phloem: sieve elements plus some

parenchyma and often some

sclerenchyma.

⚫ Two types of sieve elements:

⚫ Sieve cells and sieve tube members.


⚫ Vascular bundles (V.B.)

⚫ Xylem and phloem occur together as vascular bundles.

⚫ Located just interior to the cortex.

⚫ In monocots, V.B. are distributed as a complex network throughout the inner part of the stem, between the bundles are parenchyma cells.


⚫ In eudicots, V.B. are arranged in one ring

surrounding the pith, a region of

parenchyma similar to the cortex.

⚫ Vascular bundles are collateral when the

phloem is on the outside and the xylem

towards the inside. In some species the

bundles are bicollateral, xylem between

outer and inner phloem.

⚫ Fig. 11 and 12.


Fig. 11. Collateral vascular

bundle.


Fig. 12 Bicollateral

vascular bundle.

1. Outer phloem.

2. Inner phloem.

3. Vessels.

4. Sieve tube.

5. Vascular cam-

bium.

6. Sclerenchyma

7. Cortex.

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