The Plant Body

1
The Plant Body
2
(No Transcript)
3
Apical Dominance

• Usually the growing terminal bud inhibits the
  development of the lateral buds, a phenomenon
  known as apical dominance - as the distance
  between the shoot tip and lateral buds, the
  influence of the apical meristem lessens and the
  lateral buds proceed with their development

4
Apical Dominance
5
Stem Function

• The two main functions of the stems are
  conduction and support
• Conduction involves moving substances
  manufactured in the leaves through the phloem to
  other parts of the plant including developing
  leaves, stems, roots, developing flowers, seeds
  and fruits and the xylem carries water from the
  roots to the leaves, where water is transpired
• Support involves holding the plant off the ground
  - supporting the principal photosynthetic organs
  of the plant (the leaves) as well as flowers,
  seeds and fruits

6
(No Transcript)
7
Stem Growth

• The organization of the apical meristem of the
  stem is more complex than is the organization of
  the apical meristem of the root
• The apical meristem adds cells to the plant body
  and forms leaf primordia and bud primordia that
  develop into lateral branches
• The apical meristem of a stem lacks a protective
  cover like the root cap of roots

8
Stem Growth contd

• Protoderm always originates from the outermost
  meristem cell layer
• Procambium and part of the ground meristem (which
  will form the cortex and sometimes part of the
  pith) form from the peripheral meristem
• The rest of the ground meristem (which forms some
  or all of the pith) is formed by the pith meristem

9
(No Transcript)
10
More Stem Growth

• Usually the meristematic activity causing the
  elongation of the internodes is most intense at
  the base of the developing internodes - if
  elongation of the internodes occurs over a long
  period, the meristematic base of the internode
  may be called an intercalary meristem (a
  meristematic region between two highly
  differentiated regions) intercalary meristems
  are very important in the growth of grasses and
  grass-like plants

11
(No Transcript)
12
(No Transcript)
13
(No Transcript)
14
Three types of primary structure

• 1. In some conifers and dicots, the narrow,
  elongated procambial cells (and consequently the
  primary vascular tissues that develop from them)
  appear as a more or less continuous hollow
  cylinder within the ground tissue - the outer
  region of the ground tissue is called the cortex
  and the inner region is the pith

15
Basswood stem cross-section
16
Three types of primary structure

• 2. In other conifers and dicots, the primary
  vascular tissues develop as a cylinder of
  discrete strands separated from one another by
  ground tissue
• The ground tissue separating the procambial
  strands (and later mature vascular bundles) is
  continuous with cortex and pith and is called the
  interfascicular parenchyma (between the bundles)
• The interfascicular regions are often called pith
  rays

17
Sunflower stem cross-section
18
Three types of primary structure

• 3. In most monocots and some herbaceous dicots,
  the arrangement of procambial strands and
  vascular bundles is more complex - vascular
  tissues do not appear as a single ring, but
  instead develop as more than one ring or are
  scattered throughout the ground tissue - here
  ground tissue cannot be distinguished as pith and
  cortex - often called pith

19
Corn stem cross-section
20
Twig structure
21
Leaf Traces

• At each node, one or more vascular bundles
  diverge from the cylinder of strands in the stem,
  cross the cortex and enter the leaf or leaves
  attached at that node
• The extensions from the vascular system in the
  stem toward the leaves are called the leaf traces
• The wide gaps or regions of ground tissue above
  the level where leaf traces diverge toward the
  leaves are called leaf gaps

22
(No Transcript)
23
(No Transcript)
24
(No Transcript)
25
(No Transcript)
26
Plant habitat and leaf structure

• mesophytes - plants that require abundant soil
  moisture and a fairly humid environment - the
  most common plants - typically have fairly well
  developed epidermis, especially on upper surface
  of leaf, stomata on both sides of leaf
• hydrophyte - plants that depend on a very
  abundant supply of water or which grow wholly or
  partially submerged in water - have thin
  epidermis, stomata only on upper surface
• xerophyte - plants adapted to arid habitats -
  very thick epidermis, stomata open to stomatal
  crypts with protective hairs

27
(No Transcript)
28
(No Transcript)
29
Dicot stomata
30
Red Oak Leaves
Shade Leaves Sun Leaves