Stem anatomy

Stem Anatomy, Primary and Secondary

1. DR. DILIP V. HANDE
PROFESSOR
DEPT OF BOTANY
SHRI SHIVAJI SCIENCE COLLEGE AMRAVATI
SEM-III
2020-2021

2. STEMS
•Origin
•Functions
•External
Morphology
•Internal Anatomy
•Specialized
Stems

3. Origin
•First stem of a plant develops from part of
a seed embryo called epicotyl, w/c is a
continuation of the hypocotyl

4. The Plant Body: Stems
FUNCTIONS OF STEMS
•Produces & support appendages
of plant (leaves, flowers, fruits)
•transport water and solutes
between roots and leaves.
•Stems in some plants are
photosynthetic.
•Produce & store materials
necessary for life (e.g., water,
starch, sugar).
•In some plants, stems have
become adapted for specialized
functions.

5. Stems support a display of
leaves.
Stems orient the leaves
toward the light with minimal
overlap among the leaves.

6. The stem supports a display of flowers

7. The stem does photosynthesis…
and stores water.
Opuntia-prickly pear

8. This stem does
photosynthesis, stores
water, but also produces a
defense chemical:
mescaline…a hallucinogen.
Lophophora williamsii-peyote

9. Two Types of Aerial Stems
Herbaceous Stems
•Soft & green
•Little growth in diameter
•Tissues chiefly primary
•Chiefly annual
•Covered by epidermis
•Buds mostly naked
Woody Stems
•Tough & not green
•Considerable growth in
diameter
•Tissues chiefly secondary
•Chiefly perennial
•Covered by corky bark
•Buds chiefly covered by
scales

10. Herbaceous Stemwoody stem

11. EXTERNAL

13. STEM APICAL MERISTEM

17. PRIMARY & SECONDARY GROWTH

18. INTERNAL STEM
ANATOMY

19. Monocotyledonous &
Dicotyledonous Flowering Plants

20. Monocot Stem –cross section

21. Typical Stem Cross Section (Dicot Stem)
Helianthusannuus-
sun flower annual
Pith
A ring of vascular bundles
Epidermis
Cortex

22. Epidermis
-window, reduce water loss
Cortex Collenchyma
-extensible support
Cortex Parenchyma
-photosynthesis, etc.
Fibers-rigid support
Functional Phloem
-conduct sugars etc. away
from leaf to rest of plant
Vascular Cambium
-adds 2°xylem and 2°phloem
Xylem
-conduct water and minerals
up from soil
Pith
-water storage, defense?

23. Stem:
outside
to center
Epidermis:reduce evaporation, gas exchange
Cortex:photosynthesis, collenchyma support
Vascular Bundles: conduction
Pith: water storage? defense? disintegrate?
Vascular Bundle:
Phloem Fibers:support
Functional Phloem:
conduct CH
2O away from leaf
Vascular Cambium:
add 2°Xylem and 2°Phloem
Xylem:
conduct minerals up from soil
outside
to center

24. Vitis vinifera-grape

25. Vitis vinifera-grape
Notice how the vascular cambia
of adjacent vascular bundles
line up side by side.
Notice that cambium tissue
differentiates between the
bundles, connecting the cambia
together.
Remnants of the procambium:
Intrafasicular cambium
Interfasicular cambium

26. Vitis vinifera-grape
The vascular cambium makes 2°tissues:

27. Basswood –1 & 2 years old

28. Three years of Secondary Growth
Tilia-basswood
Secondary
Xylem
Secondary
Phloem

29. A cork cambium differentiates and produces a periderm.
Epidermis
Cork Cambium
Phelloderm
cutin
suberin
Cork Cells

30. Over time, the epidermis dies.
The cork cells build up to for
a thick layer for the bark of a
tree. We use this to make
stoppers for wine bottles and
so on.
When suberin is fully
developed, the cortex cells
will eventually be in the
dark. So these chloroplasts
will lose their function!

31. Bark =
epidermis +
periderm +
cortex +
phloem +
vascular
cambium
Wood =
secondary
xylem only!
Pith =
a small
percentage of
tree diameter
at maturity

32. Anatomy of a Woody Stem

33. Sequoia sempervirens-giant sequoia
The trees pictured below have long lost their
epidermis on the woody portion of the stem

34. The study of the growth rings in wood: Dendrochronology

35. Each year the cambium
produces a layer of secondary
xylem and a layer of secondary
phloem.
This photo shows secondary
xylem from parts of three years
in Pinus strobus(white pine).
mid-summer of one year
fall of that year
winter of that year
spring of the nextyear

36. Stems
Stems—the axes of plants—consist of nodes(where
leaves and axillary buds are produced) separated by
internodes.

37. Node-region of the stem where the leaf and bud are
borne.
Internode-the part of the stem between two adjacent
nodes.
Herbaceous-not woody; dying down at the end of the
growing season.
Woody-hard in texture, containing secondary xylem, and
persisting more than one growing season.
Acaulescent-having an inconspicuous stem.
Caulescent-having a distinct stem.

38. Modified & Specialized Stems

39. Bulbs
•Bulbs -large buds
with a small stem at
the lower end
surrounded by
numerous fleshy
leaves that store
nutrients; adventitious
roots at base
•Eg. onion, tulip, hyacinth,
daffodil and lily

40. Corms
•Corms -resemble
bulbs but composed
entirely of stem tissue
surrounded by a few
papery scale like
leaves,food storage
organs with
adventitious roots at
the base of corms
•Eg. crocus and
gladiolus.

41. Rhizomes
•Rhizomes -horizontal
stems that grow
below the ground with
adventitious roots
•Eg. irises, ferns, and
grasses.

42. Cladophylls
•Cladophylls or
cladodes -leaf-like
stemsmodified for
photosynthesis
•Eg. butcher's broom,
asparagus, orchids (eg.
Epidendrum)

43. Succulent Stems
•Succulent stems -
stout fleshy stems
that are modified for
water and food
storage
Eg. cacti

45. Thorns-for protection from grazing animals
•Bougainvillea
•Honey locust (modified
stem)
•Black Locust (modified
leaf stipules)

46. Food Storage Stems
Prickly Pear
Cactus
Bamboo Shoots
Kohlrabi

47. Food Storage Stems -Sugarcane

48. Tubers
•Tubers –swollen
regions of stems that
store food for
subsequent growth
•The "eyes" of a potato
(irish potatoes Solanum
tuberosum) are the nodes
of a starch-ladened stem

49. Stolons
•Stolons or runners -
horizontal stem that
grow above the
ground with long
internodes
Eg. Bermuda grass
(Cynodon dactylon)
Spider plant (Chlorophytum)
Fern (Nephrolepis)
Bermuda grass (Cynodon dactylon).