Plant Structure, Growth, and Development

Page
6

Cortex

Emerging

lateral

root

Vascular

cylinder

100 µm

Epidermis

Lateral root

3

2

1

Slide 43

Primary Growth of Shoots - Apical Meristems

A shoot apical meristem is a dome-shaped mass of dividing cells at the shoot tip.

Axillary buds develop from meristematic cells left at the bases of leaf primordia.

Lateral shoots develop from axillary buds on the stem’s surface.

In most eudicots, the vascular tissue consists of vascular bundles that are arranged in a ring.

Slide 44

Shoot tip

Shoot apical meristem

Leaf primordia

Young

leaf

Developing

vascular

strand

Axillary bud

meristems

0.25 mm

Slide 45

Organization of primary tissues in young stems

Phloem

Xylem

Sclerenchyma

(fiber cells)

Ground tissue

connecting

pith to cortex

Pith

Cortex

1 mm

Epidermis

Vascular

bundle

Cross section of stem with vascular bundles forming

a ring (typical of eudicots)

(a)

Key

to labels

Dermal

Ground

Vascular

Cross section of stem with scattered vascular bundles

(typical of monocots)

(b)

1 mm

Epidermis

Vascular

bundles

Ground

tissue

Slide 46

In most monocot stems, the vascular bundles are scattered throughout the ground tissue, rather than forming a ring.

Slide 47

Tissue Organization of Leaves

The epidermis in leaves is interrupted by stomata, which allow CO2 exchange between the air and the photosynthetic cells in a leaf.

Each stomatal pore is flanked by two guard cells, which regulate its opening and closing.

The ground tissue in a leaf, called mesophyll, is sandwiched between the upper and lower epidermis.

Slide 48

Below the palisade mesophyll in the upper part of the leaf is loosely arranged spongy mesophyll, where gas exchange occurs.

The vascular tissue of each leaf is continuous with the vascular tissue of the stem.

Veins are the leaf’s vascular bundles and function as the leaf’s skeleton.

Each vein in a leaf is enclosed by a protective bundle sheath.

Slide 49

Leaf anatomy

Key

to labels

Dermal

Ground

Vascular

Cuticle

Sclerenchyma

fibers

Stoma

Bundle-

sheath

cell

Xylem

Phloem

(a) Cutaway drawing of leaf tissues