1. Shoot System
-Stem-
Prepared by:
Group III
BS Bio 1-C

2. Stems
 The main body of the
portion above the
ground of the tree,
shrub, herb, or other
plant; the ascending
axis, whether above or
below the ground of a
plant, in contradiction
to the descending axis
or root.

3. MAJOR FUNCTIONS
OF STEMS
-Stems support
-Stems Conduct
-Stem produce new ling tissue

4. STEMS SUPPORT
 Provides mechanical support and raise leaves into the
air, thus facilitating photosynthesis. Flowers and fruits
are also produced in position, for facilitating
pollination and seed dispersal.
STEMS CONDUCT
o Provides a pathway for movement of water and mineral
nutrients from roots to leaves and for transfer of foods ,
hormones and to other metabolites from one part to
another.
STEMS PRODUCE NEW LIVING TISSUE
o Provide new living tissue for normal metabolism of
plant.

5. EXTERNAL
PLANT
MORPHOLOGY

6. A stem is an organ consisting of
 An alternating system of nodes, the points at
which leaves are attached
 Internodes, the stem segments between
nodes

7.  An axillary bud is a structure that has the
potential to form a lateral shoot, or branch
 An apical bud, or terminal bud, is located near
the shoot tip and causes elongation of a young
shoot
 Apical dominance helps to maintain dormancy
in most non-apical buds
 Lenticels are structure that permit the passage of
gas inward and outward.
 Leaf scar are characteristic scar on stem axis
made by leaf abscission.
 Bud scales are small modified leaves for
protection from desiccation.

8. Dormant shoot apex with its protective scales is a BUD.
 Bud Scars are the scars left from the removal of bud.
 Leaf primordium is an immature leaf of the
shoot.
 Intercalary meristem the portion of the internodes
above the node . Made up of actively dividing cells
responsible for the elongation of the monocot stem.

10. Apical bud
Fig. 35-12 Bud scale
Axillary buds
This year’s growth
(one year old) Leaf
scar
Bud Node
One-year-old side
scar branch formed
Internode from axillary bud
near shoot tip
Last year’s growth
(two years old) Leaf scar
Stem
Bud scar left by apical
bud scales of previous
winters
Growth of two
years ago
(three years old) Leaf scar

11. Shoot Apex
Organization

12. Shoot Apex
organization
 The outer group
consisting of one or
more peripheral cell
layer is known as the
TUNICA. These cells
divide anticlinally
(perpendicular to the
surface of the shoot
apex)
 The CORPUS lies
below the tunica and
initially has a single
layer of cells. Corpus
cells divide anticlinally
and periclinally
(parallel to the surface
of the shoot apex.)

13.  A shoot apical meristem is a dome-
shaped mass of dividing cells at the shoot
tip
 Leaves develop from leaf primordia
along the sides of the apical meristem
 Axillary buds develop from
meristematic cells left at the bases of leaf
primordia

14. Fig. 35-16
Shoot apical meristem Leaf primordia
Young
leaf
Developing
vascular
strand
Axillary bud
meristems
0.25 mm

15. Primary Meristems
 Protoderm- the outermost layer of cells.
It develops into epidermis--- the special
primary tissue that covers and protects all
underlying primary tissues. The epidermis
prevents excessive water loss and yet
allows for exchange of gases necessary for
respiration and photosynthesis.

16. Primary Meristems
 Ground meristem- Comprises the
greater portion of meristematic tissue of
the shoot tip. Primary tissues forming
from the ground meristem are:
a) Pith- in the very center of stem
b) Cortex- in a cylinder just beneath the
epidermis and surrounding the vascular
tissues. Sometimes pith and cortex are
connected by pith rays.

17. Primary Meritsems
 Procambium cells give rise to
primary vascular tissues
namely;
a) Primary phloem
b) Primary xylem

18. STEM ANATOMY,
PRIMARY
STRUCTURE

19. • Meristems are perpetually embryonic tissue and
allow for indeterminate growth
• Apical meristems are located at the tips of roots
and shoots and at the axillary buds of shoots
• Apical meristems elongate shoots and roots, a
process called primary growth

20.  Stems undergo primary growth
which results in the formation of
primary tissues. These include the
 Epidermis
 Ground tissue
 primary vascular tissues
(primary xylem and primary
phloem)

21. The young dicot stem

22. Summary of Primary Development
Protoderm Epidermis
Ground meristem Cortex
Apical Meristem Pith and pith
rays
Procambium Phloem
Vascular Cambium
Xylem

23. Primary Growth development
 The term stele is applied to the part of the stem that includes
primary vascular tissues, pith, and pith rays. The primary plant
body is composed of the above primary tissues.
 The main functions of these primary tissues may be
summarized as shown below.
 Epidermis: Protects underlying tissues.
Vascular tissues
 Phloem: Conducts Food
 Vascular Cambium: produces secondary phloem and secondary
xylem

24.  Xylem: conducts water and mineral salts , and gives
strength to stem.
Cortex: Stores food and in young stems, manufactures
food, strengthens and protects.
Pith: Stores food
Pith rays: Store food, and conduct water, mineral salts,
and food radically.

25. The young dicot stem
 The stellar type exhibited by a dicot
stem is a EUSTELE.
 The type of xylem maturation is
known as Endarch.
 Secondary growth is present.

26. THE MONOCOT
STEM

27. Fig. 35-17b
Ground
tissue
Epidermis
Key
to labels
Vascular
Dermal bundles
Ground
1 mm
Vascular (b) Cross section of stem with scattered vascular bundles
(typical of monocots)

28. The monocot stem
 The vascular bundles are scattered
throughout the ground tissue. The type of
stele exhibit is ATACTOSTELE.
 In most monocot stems, the vascular
bundles are scattered throughout the
ground tissue, rather than forming a ring.
 They do not have secondary growth.

29. Fig. 35-17
Phloem Xylem
Sclerenchyma Ground
Ground tissue
(fiber cells) tissue
connecting
pith to cortex
Pith Epidermis
Key
to labels
Epidermis Cortex Vascular
Dermal bundles
Vascular
bundle Ground
1 mm Vascular 1 mm
(a) Cross section of stem with vascular bundles forming (b) Cross section of stem with scattered vascular bundles
a ring (typical of eudicots) (typical of monocots)

30. Eustele vs. Atactostle

31. STEM
ANATOMY, SECONDA
RY STRUCTURE

32. • Secondary growth occurs in stems and
roots of woody plants but rarely in leaves
• The secondary plant body consists of the
tissues produced by the vascular cambium
and cork cambium
• Secondary growth is characteristic of
gymnosperms and many eudicots, but not
monocots

33. Woody dicot (Tillia sp.)

34. Stem anatomy, secondary structure
These tissue layers form the Periderm.
 The outermost layer is the phellem,
consisting of cork cells.
 Immediately inner to it is the phellogen, or
the cork cambium, consisting of flattened
dividing cells.
 The third layer is the pheloderm, few cell
layers in thickness.

35. Fig. 35-19a1
(a) Primary and secondary growth Pith
in a two-year-old stem Primary xylem
Vascular cambium
Epidermis Primary phloem
Cortex Cortex
Primary phloem Epidermis
Vascular cambium
Primary xylem
Pith
Periderm (mainly
cork cambia
and cork)
Secondary phloem
Secondary
xylem

36. Fig. 35-19a2
(a) Primary and secondary growth Pith
in a two-year-old stem Primary xylem
Vascular cambium
Epidermis Primary phloem
Cortex Cortex
Primary phloem Epidermis
Vascular cambium
Vascular ray
Primary xylem
Secondary xylem
Pith
Secondary phloem
First cork cambium
Cork
Periderm (mainly
cork cambia
and cork)
Secondary phloem
Secondary
xylem

37. Fig. 35-19a3
(a) Primary and secondary growth Pith
in a two-year-old stem Primary xylem
Vascular cambium
Epidermis Primary phloem
Cortex Cortex
Primary phloem Epidermis
Vascular cambium
Vascular ray
Primary xylem
Secondary xylem
Pith
Secondary phloem
First cork cambium
Cork
Periderm (mainly Most recent cork
cork cambia cambium
and cork)
Cork
Secondary phloem Bark
Layers of
periderm
Secondary
xylem

38. Fig. 35-19b
Secondary phloem Bark
Vascular cambium
Late wood Cork
Secondary xylem cambium Periderm
Early wood
Cork
0.5 mm
Vascular ray Growth ring
(b) Cross section of a three-year-
old Tilia (linden) stem (LM)
0.5 mm

39. The Vascular Cambium and Secondary
Vascular Tissue
 The vascular cambium is a cylinder of meristematic
cells one cell layer thick
 It develops from undifferentiated parenchyma cells

40.  In cross section, the vascular cambium appears
as a ring of initials
 The initials increase the vascular cambium’s
circumference and add secondary xylem to the
inside and secondary phloem to the outside

41.  Secondary xylem accumulates as wood, and
consists of tracheids, vessel elements (only in
angiosperms), and fibers
 Early wood, formed in the spring, has thin cell walls
to maximize water delivery
 Late wood, formed in late summer, has thick-walled
cells and contributes more to stem support
 In temperate regions, the vascular cambium of
perennials is dormant through the winter

42.  Tree rings are visible where late and early
wood meet, and can be used to estimate a
tree’s age
 Dendrochronology is the analysis of tree ring
growth patterns, and can be used to study
past climate change

43.  As a tree or woody shrub ages, the older
layers of secondary xylem, the heartwood,
no longer transport water and minerals
 The outer layers, known as sapwood, still
transport materials through the xylem
 Older secondary phloem sloughs off and
does not accumulate

44. Fig. 35-22
Growth
ring
Vascular
ray
Heartwood
Secondary
xylem Sapwood
Vascular cambium
Secondary phloem
Bark
Layers of periderm

45. The Cork Cambium and the
Production of Periderm
 The cork cambium gives rise to the secondary
plant body’s protective covering, or periderm
 Periderm consists of the cork cambium plus the
layers of cork cells it produces
 Bark consists of all the tissues external to the
vascular cambium, including secondary phloem
and periderm
 Lenticels in the periderm allow for gas
exchange between living stem or root cells and
the outside air

46.  A plant can grow throughout its life; this is
called indeterminate growth
 Some plant organs cease to grow at a certain
size; this is called determinate growth
 Annuals complete their life cycle in a year
or less
 Biennials require two growing seasons
 Perennials live for many years

47. Sequoia sempervirens

48. Pinus aristata

49. Monocot vs.Dicot
Parameter Monocot Dicot
Extent of cortex No distinct cortex Cortex found at the
outer part of ground
tissue
Presence or absence of Absent Present
pith
Type of stele Atactostele Eustele
Presence or absence of Absent Present
vascular cambium

50. Modified Stem
Modification of the stem would depend on
the need of the plant to survive…
… like the animals it learns how to
adapt.

51.  Bulb – consist of small amount
of vertical stem and a massive
quantity of thick, fleshy storage
leaves.
- most of them consist of
concentric rings of scales
attached to a basal plate.
.

53. Other bulbous plants
Daffodil Reticulate iris

54. Stolon / runner = with long
internodes just below the
surface of the ground that
typically terminating in a new
plant
= use for propagation

55. Fig. 35-5c
Stolon
Stolons

56. Corm - formed from a swollen bases
of stems.
- A corm consists of one or
more internodes with at least one
growing point

57. Examples of Corm
Crocuses Gladioli

58. Rhizome= the stem is
horizontal and underground
with short internodes and
bearing with scale-like leaves.

59. Other rhizome plants
Cogon grass Johnson grass
Imperata cylindrica Sorghum halepense

60. Tuber = a thick under ground
storage stem, usually not upright
= bearing outer buds
= lacking protective scales

61. Fig. 35-5d
Tubers

62. Aerial MODIFICATIONS OF STEM
•TENDRILS
IN grapes
Axillary bud is modified
into tendrils.
•CLADOPHYLL /
PHYLLOCLADE
The entire shoot is
flattend & leaf like.

63. References
• Campbell, N.A., J.B Reece and L.G. Mitchell.
1999. Biology. 5th ed. USA: The
Benjamin/Cummings Publishing Co. Inc.
• Weier, E.T., R.C Stocking., M. G Barbour and Rost
T. L.1982. Botany an Introduction to Plant
Biology. 6th ed. USA: John Willey and Sons Inc.

64. THANK YOU!
THE END