Welcome to the comprehensive PowerPoint presentation designed for 11th-grade students, covering an in-depth study of root and stem morphology. In this engaging presentation, I delve into the fascinating world of plant structures, exploring various modifications and key points that define their functions.

1. STEM AND STEM
MODIFICATION
CLASS-XI
By
Pintu Barik

2. INTRODUCTION TO STEM
• Stem develops from the plumule
of the embryo
• It is the ascending part of the
main plant axis
• Functions of the stem: bearing
branches, leaves, flowers, fruits,
conducting water and mineral salts

3. NODES AND INTERNODES
• Stem is differentiated into
nodes and internodes
• Nodes: regions where leaves
are born
• Internode: the part of the
stem between two nodes

4. UNDERGROUND STEM MODIFICATIONS
• Certain plants have stems that
develop underground
• Categories of underground
stem modifications:
a) Rhizome
b) Tuber
c) Bulb
d) Corm

5. a) Rhizome
• Horizontal underground stem
• Fleshy, dorsiventral, and
perennial
• Examples: Dryopteris, banana,
lotus, ginger, canna indica,
turmeric

6. b) Tuber
•Lower branches of stem
become positively
geotropic and buried in
soil
•Accumulation of food
(starch) in the tip of
underground branches
•Examples: Potato,
Jerusalem artichoke

7. c) Bulb
•Stem highly reduced,
leaves become
condensed and fleshy
for storage
•Stem reduced to disc-
shaped structure
•Examples: Onion, Tulipa,
garlic, lily

8. d) Corm
•Short, thick, and highly
condensed form of
rhizome
•Buds at nodes and
adventitious roots at
the base
•Examples:
Amorphophallus, Crocus,
Alocasia

10. Introduction
• In subaerial stem modifications, a
part of the stem remains
underground, while the remaining
part becomes aerial.
• Dormant buds on the stem
become active and develop lateral
branches for vegetative
reproduction.

11. Runners
• Runners have weak, long, and thin
internodes.
• They creep over the surface of the
soil, serving as a means of
vegetative propagation.
• Examples include doob grass or lawn
grass (Cynodon dactylon), brahmi
booti (Centella asiatica), and wood
sorrel (Oxalis).

12. Suckers
• Suckers are axillary branches
that initially grow horizontally
from the node of an
underground stem.
• They then grow obliquely
upward to serve as new plant
shoots.
• Examples include
Chrysanthemum and banana.

13. Stolons
• Stolons are long lateral
branches that arise from the
base of the stem.
• They grow aerially for a
certain distance and then
arch downward to touch the
ground.
• Stolons give rise to new
daughter plants.
• Examples: Strawberry
(Fragaria), Mint (Mentha),
Couch Grass (Elymus repens)

14. Offsets
• Offsets are lateral
branches with short
internodes.
• Each node bears a
rosette of leaves upward
(aerial) and a cluster of
roots downward.
• Examples include water
lettuce (Pistia) and water
hyacinth (Eichhornia
crassipes).

15. Difference between Stolons and Runners
•Stolons grow below the surface of the
soil, while runners grow above the
surface.
•Both serve as means of vegetative
reproduction.

17. Introduction:
• Aerial stem modification refers
to the transformation of the
main stem into specialized
structures with unique
functions.
• These modifications are
observed in various plants to
adapt to specific environmental
conditions and perform specific
functions.

18. Stem Tendrils
• When the stem is weak, the
axillary or terminal bud
undergoes modification into
tendrils.
• Tendrils enable plants to climb
and support themselves.
• Examples include Vitis
(modified apical bud) and
Passiflora (modified axillary
bud).

19. Stem Thorns
• The axillary bud gets transformed
into thorns, which can serve as
climbing aids or defense mechanisms.
• Thorns can be found in the axils of
leaves or at the apex of the stem.
• Examples include Duranta, climbing
rose (with curved prickles),
Asparagus (with leaf spines),
Bougainvillea (with extra axillary
thorns), and Calamus (with leaf
sheath spines).
• It's important to note that thorns
are modified stems, while spikes are
modified leaves.

20. Phylloclades
• Phylloclades are flattened,
thick, succulent, green stems
that perform photosynthesis.
• They allow plants to thrive in
dry and xerophytic habitats.
• Phylloclades can be flattened
(e.g., Opuntia, Muchlenbeckia =
Coccoloba, Epiphyllum) or
cylindrical (e.g., Casuarina,
Euphorbia royleana, E. tirucalli).

21. Cladodes (Cladophylls)
• Cladodes are green, one
internode long stems that
develop from the axillary buds.
• They function as photosynthetic
organs, replacing the role of
leaves.
• True leaves in these plants are
typically reduced to scales or
spines.
• Examples include Asparagus and
Ruscus.

22. Bulbil
• A bulbil is a modified stem that
develops from a vegetative or
flower bud.
• It becomes swollen due to the
accumulation of food reserves.
• When detached from the
parent plant, it can give rise to
a new plant.
• An example is Dioscorea
bulbifera.