1. Stem

2. FUNCTIONS
 1. Conduction of food and water
 2. Formation and support of leaves and buds
 3. Storage of food
ORIGIN OF STEMS
 Epicotyl is the embryonic origin of stems
 Plumule is the first bud
 The 2 terms are
sometimes used
synanymously

3. EXTERNAL STRUCTURE OF STEMS
 Nodes
 Internodes
 Leaves
 Buds
 Leaf scar
 Vascular bundle scar
 Bud scales
 Bud scale scar
 Lenticels

5. Primary growth of the plant body

7. Protoderm
Ground meristem
Procambium

8. PRIMARY PERMANENT TISSUES

9. PRIMARY PERMANENT TISSUES
 1. Epidermis
 2. Cortex
 3. Vascular tissues
 4. Pith
 5. Endodermis
 6. Pericycle

10.  3. Vascular tissues
 A. Primary xylem
 Protoxylem –
 First part of the 10 xylem to mature
 Made up of tracheary elements and
parenchyma
 Metaxylem‐
 Later part of the 10 xylem to mature
 With tracheary elements, parenchyma
and fibers

12. Primary xylem development
 EXARCH – First xylem elements to mature are
farthest from the center of the axis;
maturation in centripetal direction
 ENDARCH‐ The initial elements occur nearest,
and the latest farthest, from the center of the
axis; maturation is centrifugal
 3. MESARCH – Differentiation progresses in 2
or more directions from the first mature xylem
elements

13. Primary xylem development
Left to right‐ A. Lycopodium flabelliforme rhizome; B. Osmunda ;
C. Quercus stem

14. B. PRIMARY PHLOEM
 PROTOPHLOEM‐ With sieve elements, may
have no companion cells; function for a short
period of time, destroyed in rapidly elongating
organs
 METAPHLOEM ‐ With sieve elements,
companion cells and parenchyma; in dicots
fibers are absent
 CENTRIPETAL DIRECTION of differentiation
 CENTRIFUGAL DIRECTION of differentiation

15. Primary phloem in Zea mays

16. Vascular bundle of Ranunculus

17. Ricinus hypocotyl

18. Vascular bundle in Cucurbita maxima

19. VASCULAR BUNDLES‐ Strands of conducting
tissue
TYPES:
 A. COLLATERAL BUNDLE‐ A bundle with
phloem on one side of xylem only, commonly
external to it
 1. CLOSED –Without vascular cambium
 2. OPEN‐ With vascular cambium
 B. BICOLLATERAL BUNDLE‐ A bundle with
phloem on both sides of the xylem

20. VASCULAR BUNDLES
TYPES:
 C. CONCENTRIC BUNDLES – A bundle where
one vascular tissue surrounds the other
 1. AMPHIVASAL‐ A bundle where the xylem
surrounds the phloem
 2. AMPHICRIBRAL – A bundle where the
phloem surrounds the xylem

21. Types of bundle

22. Types of bundle

23. PRIMARY PERMANENT TISSUES
 1. Epidermis
 2. Cortex
 3. Vascular tissues
 4. Pith
 5. Endodermis
 6. Pericycle

24.  4. PITH
 5. ENDODERMIS‐ the innermost layer of the
cortex
 6. PERICYCLE‐ the fundamental tissue of the
stele; the fundamental tissue between the
endodermis and the vascular cylinder
 STELE‐ made up of the vascular system and
conjunctive tissue (interfascicular regions,
the gaps, the pith, if present) and the pericycle

25. Starch sheath in Ricinus

26. Perivascular fibers in Cucurbita

27. TYPES OF STELE
 PROTOSTELE‐ Solid column of vascular tissue
without pith
 A. HAPLOSTELE –solid core of xylem
surrounded by the phloem e.g., Selaginella
 B. ACTINOSTELE‐ the xylem tissue is star‐
shaped and surrounded by the phloem e.g.
Psilotum
 C. PLECTOSTELE‐ the xylem strands are in
longitudinal files or in a platelike arrangement
and the phloem tissues are interspersed with
the xylem tissues e.g. Lycopodium

28.  TYPES OF STELE
 SIPHONOSTELE‐ vascular tissue surrounds a
non‐vascular core, the pith
 A. ECTOPHLOIC SIPHONOSTELE‐ the
phloem occurs outside the xylem cylinder
 B. AMPHIPHLOIC SIPHONOSTELE
(SOLENOSTELE)‐ the phloem differentiates
outside and inside the xylem cylinder
 DICTYOSTELE‐ a siphonostele in which large
gaps are large so that stele is divided into
separate bundles

30.  EUSTELE‐ a stele with interfascicular
parenchyma and collateral or bicollateral
bundles
 ATACTOSTELE‐ a stele with scattered bundles

31. NODES AND INTERNODES (ANATOMY)
 1. Differ in arrangement of vascular tissues
 A. LEAF TRACE‐ a vascular bundle located in
the stem but directly related to the leaf
 B. LEAF GAP OR LACUNAE ‐ the parenchyma
region located adaxially from the diverging leaf
trace

32. Leaf trace and gap

33. NODES AND INTERNODES (ANATOMY)
 TYPES OF NODE
 1. ONE‐TRACE UNILACULAR‐ with a single
gap and a single trace to a leaf
 2. TWO‐TRACE UNILACULAR‐ with 2 traces
and a single gap to a leaf
 3. TRILACUNAR‐ with 3 traces and 3 gaps to a
leaf (1 median and 2 lateral)
 4. MULTILACUNAR‐ with several to many
gaps and traces to a leaf

34. Types of node

35. Types of node

36. NODES AND INTERNODES (ANATOMY)
 1. Differ in arrangement of vascular tissues
 C. BRANCH TRACES‐ vascular supply of the
branch located on the stem
 D. BRANCH GAP‐ the parenchyma region in
the vascular cylinder above the position where
the branch trace enters the branch

37. NODES AND INTERNODES (ANATOMY)
 2. The cortical and pith cells may be shorter in
the nodes and there may be less sclerenchyma
and more collenchyma
 3. If the pith is destroyed during the growth of
the stem,
 the node retains the pith (nodal diaphragm)
while the internode is hollow
 or series of horizontal plates of pith are left
(diaphragmed pith)

38. Cucurbita stem

39. PRIMARY GROWTH OF THE AXIS
 INCREASE IN HEIGHT
 primarily through growth of internodes by:
 INCREASE IN DIAMETER
 AS A RESULT OF:
 diffuse growth
 cell division restricted to cortex and pith
 cell division restricted to primary thickening
meristem

40. Primary thickening meristem

41. Secondary growth of the plant
body

45. VASCULAR CAMBIUM
 forms 20 vascular tissues
 are highly vacuolated
 with primary pit fields
 CELL TYPES
 FUSIFORM INITIALS‐ elongated with
tapering ends
 RAY INITIALS – nearly isodiametric,
relatively small cells

46.  ARRANGEMENT IN TRANSECTION
 arranged in radial series‐ cells of the
cambial zone (initials and immediate
derivatives)

47.  ARRANGEMENT IN TANGENTIAL VIEWS
 1. STORIED OR STRATIFIED CAMBIUM –
fusiform initials in horizontal tiers with the
ends of cells appearing at exactly the same
level
 2. NONSTORIED OR NONSTRATIFIED
CAMBIUM‐ the fusiform initials are not in
horizontal tiers; their ends overlap (more
primitive)

48. Vascular cambium in tangential section

49.  CELL DIVISION
 1. MULTIPLICATIVE DIVISIONS – radial
(anticlinal) divisions that increase the number
of initials
 2. ADDITIVE DIVISIONS – tangential
(periclinal) divisions that contribute cells to the
secondary xylem and secondary phloem

51. Multiplicative divisions in
fusiform initials

52.  DEVELOPMENTAL CHANGES
 New rays may arise from fusiform initials or
their segments
 1. from the apex of fusiform initial
 2. from the side of fusiform initial
 3. by transverse divisions of a fusiform initial
 INCREASE IN WIDTH AND HEIGHT OF RAYS
MAY RESULT FROM:
 1. radial divisions of a ray initial
 2. fusion of 2 or more groups of ray initials (by
changes in the intervening fusiform initials
(loss of some, division and conversion to ray
of others)

53. Origin of rays from fusiform initials

54. Increase in width of ray

55. Increase in height of ray

56. Increase in height of ray

57.  SPLITTING OF RAYS
 1. through intrusive growth of fusiform initials
from a group of ray initials
 2. through elongation of ray initials into
fusiform initials is less common
 LOSS OF INITIALS
 1. FUSIFORM INITIALS
 A. conversion to ray initials
 B. maturation into 20 xylem or 20 phloem
elements

58. Splitting of rays

59.  LOSS OF INITIAL
 2. RAY INITIALS
 A. maturation into 20 xylem or 20 phloem
elements

61. STORIED AND NONSTORIED WOODS
 1) NONSTORIED CAMBIUM ‐ forms nonstoried wood
 2) STORIED CAMBIUM – forms storied or nonstoried
wood
GROWTH RINGS/ANNUAL RINGS
 EARLY WOOD (SPRING WOOD) – less dense,
larger cells and smaller amount of wall substance
 LATE WOOD (SUMMER WOOD) –smaller cells with
thicker walls

62. Vascular cambium in tangential section

63. Earlywood and latewood

64. Earlywood and latewood

65. SAPWOOD/HEARTWOOD
 SAPWOOD‐ functional part of the 20 xylem
 HEARTWOOD – non‐functional part of the 20
xylem

66. SECONDARY VASCULAR TISSUES
 AXIAL SYSTEM –originates from fusiform
initials
 RAY SYSTEM – originates from ray initials

68. GYMNOSPERM WOOD
 AXIAL SYSTEM
 tracheids
 fiber‐tracheids
 axial parenchyma
 RAY SYSTEM
 may be composed of ray parenchyma only or
with ray tracheids
 ray parenchyma
 ray tracheids‐ with bordered pits and lack of
protoplast; with lignified walls; occur at the
margins of ray

69. The gymnosperm wood

70. Pine wood in cross section

71.  HOMOCELLULAR RAY
 HETEROCELLULAR RAY
 resin ducts‐ in axial system or both axial system
and ray system

72. Pine wood

73. ANGIOSPERM WOOD
 more complex than gymnosperm wood
DISTRIBUTION OF VESSELS
 1. DIFFUSE POROUS‐ essentially equal
diameters of vessels and uniformly distributed
through a growth ring
 2. RING POROUS – with vessels of unequal
diameters; with the largest vessels localized in
early wood

74. Angiosperm wood

75. Secondary xylem of Populus
deltoides

76. Wood of Quercus alba

77. DISTRIBUTION OF AXIAL PARENCHYMA
 1. APOTRACHEAL TYPE‐ the position of
parenchyma is independent of that of vessels
 A. DIFFUSE – dispersed throughout the
growth ring
 B. BANDED – appear in bands
 C. MARGINAL – limited to the periphery
 1) INITIAL PARENCHYMA – restricted to
the beginning of a seasonal increment
 2)TERMINAL PARENCHYMA‐ restricted to
the end of a seasonal increment

78. Portion of the Wood of Quercus alba

79. Apotracheal banded

80. Secondary xylem of Zygophyllum
dumosum

81.  2. PARATRACHEAL TYPE‐the two kinds of
elements are associated with one another
 A. SCANTY ‐ occasional parenchyma cells
associated with the vessels
 B. VASICENTRIC‐ surrounding the vessel
 C. ALIFORM – vasicentric with wing‐like
tangential extensions
 D.CONFLUENT – coalesced aliform with
forming irregular tangential or diagonal bands

82. scanty vasicentric

83. STRUCTURE OF RAY
 with ray parenchyma only
 HOMOCELLULAR RAY – if it contains only
procumbent or upright ray
 HETEROCELLULAR RAY – if it contains both
types morphologically
RAY SYSTEM
 HOMOGENEOUS RAY –rays are all homocellular
 HETEROGENEOUS RAY – rays are all
heterocellular or some are homocellular, others
heterocellular

84. SECONDARY GROWTH IN MONOCOTYLEDONS
 the activity of this meristem resembles that
concerned with the primary thickening in some
monocots
 these meristems may be developmentally
continuous if found in the same plant
TYPES OF 20 GROWTH IN MONOCOTS
 diffuse 20 growth through division and
enlargement of ground parenchyma (e.g. palms)
 20 growth from a restricted meristem (cambium)
formed in the cortex outside the vascular
bundles (herbaceous and woody Liliflorae e.g.
Aloe, Sansevieria, Yucca, Agave, Dracaena)

85. Primary thickening meristem

86. SECONDARY GROWTH IN MONOCOTYLEDONS

87. COMMON FORMS OF 20 GROWTH
 1. The 10 vascular tissues form an almost
continuous vascular cylinder and the 20
vascular tissues do the same
 2. The 10 vascular tissues form a system of
strands, but the 20 vascular tissues arise as a
continuous ring

88. Young stem of Tilia

89. Old stem of Tilia

94. ANOMALOUS 20 GROWTH
 Deviating methods of 20 thickening
 Less common growth patterns among plants
investigated thus far