The document discusses various modifications of stems and roots in plants. It describes underground stem modifications like rhizomes, bulbs, corms and tubers which store food. Aerial stem modifications include tendrils for climbing, thorns for protection, phylloclades, cladodes and bulbils for vegetative propagation. Root modifications comprise swollen storage roots, adventitious roots for support, haustoria for parasitic absorption, floating roots for buoyancy and epiphytic roots to absorb moisture from air.

1. Plant Part
Modifications

2.  Some of the most important types of
modifications of stem are as follows:
 I. Underground modifications of Stem
 II. Subaerial modifications of Stem
 III. Aerial modifications of Stem.w
STEM MODIFICAIONS

3. Underground modifications of
Stem
 Many plants produce underground stems for
perennation and food storage. They produce
aerial shoots annually.
 Although they resemble roots superficially but
can be; distinguishable from roots by the
presence of following features:
 Presence of nodes and internodes
 Presence of scale leaves, buds and adventitious
roots at the nodes.
 Internal structure resembles that of aerial stem
and not of root.

4. Rhizome
 Fleshy, non-green
underground stem.
 Distinct nodes and
internodes.
 Nodes bear dry scale
leaves with axillary buds.
 Terminal buds also
present.
 Adventitious roots arise
from the lower side.
 e.g. Ginger, turmeric,
Canna etc

5. Bulb
 It is a highly condensed
discoid stem its upper
surface a terminal bud
and many fleshy scale
leaves are present.
 A cluster of adventitious
roots arise from the
base of the bulb.
 E,g. Lilly, Onion Garlic

6. Corm
 It is a condensed form of
rhizome growing in vertical
direction.
 It is more or less spherical with
a flattered base.
 The corm has distinct circular
nodes and internodes.
 Examples- colocasia,
Amorphophallus.

7. Tuber
 Stem tuber is a swollen tip
of an underground lateral
Stem (Stolon).
 It is covered by a number
small depressions called
eyes’.
 Each eye represents a
node, bearing one or more
buds subtended by a leaf
scar
 Adventitious roots are
usually absent e.g., Potato.

8. Subaerial modifications of
Stem
 In subaerial modifications, the stem is partly
aerial and partly underground.
 Short aerial branches and adventitious roots
develop at the nodes.
 Detachment of entire branch or a node can
develop into a new plant.
 The plants are commonly known as creepers and
their subaerial stem modifications meant for
vegetative propagation.

9. Runner
 It is a creeping stem with long
internodes, running horizontally on the
soil surface.
 The nodes bear axillary buds, scale
leaves and adventitious roots.
 Runner arises from an axillary bud.
 A mother plant often produces a number
of runners in all direction.
 Runners break off and grow into
individual plants, and thus help in
vegetative propagation.
 Examples – Cynodon (Lawn grass),
Oxalis (Wood sorrel), Centella

10. Sucker
 It arises from the basal,
underground part of the
main stem.
 It grows horizontally for a
distance under the soil and
then emerges obliquely
upwards.
 It develops a leafy shoot
and adventitious roots
before separating from the
mother plant.
 The common sucker-
bearing plants are
Chrysanthemum , Musa
(banana), Mentha

11. Stolon
 It is a weak lateral branch
that arises from the base
of main stem.
 After growing aerially for
some time it bends
downwards to touch the
ground, where its terminal
bud gives rise to a new
shoot and adventitious
roots.
 The common stolon
bearing plants are
Jasmine, Colocasia, and
Vallisneria

12. Offset
 It is a short runner with one internode long.
 It originates from leaf axil, grows as a short horizontal
branch.
 It produces a rosette of leaves above and adventitious roots
below.
 Offsets art generally found in aquatic plants like Pistia (water
lettuce), Eichornia (water hyacinth)

13. Aerial modifications of Stem
 In certain plants, the aerial stem or buds get
modified to perform special functions like
climbing, protection, food storage, vegetative
propagation etc.

14. Stem tendrils
 Stem or its branches get modified into green thread like leafless
structures called tendrils which are meant for climbing.
 These may be branched or un-branched
 Stem tendrils are of four types:
 Axillary tendrils-e.g., Passiflora
 Extra-axillary tendrils-e.g., Cucurbita, Luffa
 Leaf-opposed or Apical bud tendrils, e.g., Grapevine (Vitis)
 Floral bud or Inflorescence tendrils – e.g., Antigonon, Cardiospermum

15. Thorns
 These are straight, pointed, hard or woody
structures sometimes they bear leaves, flowers or
even may be branched. E.g.Citrus
 Thorns are used as organs of defence or climbing
(e.g. Bougainvillea) and check transpiration

16. Phylloclades
 These are fleshy, green flattened or cylindrical
branches of unlimited growth.
 The leaves are modified into spines or scales to check
transpiration.
 They take part in photosynthesis and store water.
 These are seen in xerophytic plants like Opuntia,
Euphorbia, Casuarina, etc.

17. Cladodes or Cladophylls
 These are green cylinderical or flattened leaf-like
branch of limited growth.
 In Asparagus, the cladodes are one internode
long and in Ruscus the cladodes are two
internode long.
 They help in photosynthesis.

18. Bulbil
 These are modified
vegetative or floral buds
with stored food and meant
for vegetative propagation.
 In Dioscorea, bulbils are
condensed axillary buds
while in Agava and lily the
floral buds develop into
bulbil.
 They detach to become
new plants

19. Thalamus (= Receptacle or
torus)
 It is a condensed stem axis that bears words of floral
organs -calyx, corolla, androecium and gynoecium
 In Cleome and Silene the thalamus exhibits clear
nodes and internodes.

20. ROOT MODIFICATIONS
 Root is said to be the part of a plant which
remains inside the soil.
 But there are subaerial as well as aerial roots
also.
 Root is a positively geotropic part of the plant
having a root cap and many unicellular root
hairs.

21.  Roots sometimes have
special functions to
perform and in such
cases their form and
structure differ from
those of normal roots.
 The modified roots may
be underground or
aerial.

22. Tap Root Modifications
 In some plants the tap roots store reserve
food for which they become swollen and
assume different shapes.
 Fusiform
 Napiform
 Conical
 Tuberous or tubercular
 Pneumatophores:

23. Fusiform
 It is a modified tap root.
 The primary root is swollen in the middle while
both the ends gradually taper forming a spindle
shaped structure, e.g., Radish (Raphanus sativus)

24. Napiform
 When root is almost spherical at one end and
tapering sharply at the other end, e.g.,
Brassica rapa (turnip)

25. Conical root
 Root which appears like a cone, i.e., broad at
the base and tapering gradually into a pointed
end, e.g., Daucas carota (carrot)

26. Tuberous or tubercular
 In this case, the root is thick and fleshy but
does not form any definite shape, e.g.,
Mirabilis jalapa.

27. Pneumatophores
 These roots grow vertically up
and come out of the water or
marshy soil like conical spikes.
 They occur in large numbers
around the tree trunk.
 Such roots are provided with
numerous pores (breathing
pores) through which air is
taken for respiration, e.g.,
Rhizophora.

28. Adventitious Root Modifications
 Fasciculated root: In
Dahlia and Asparagus a
number of adventitious roots
arise as a cluster, from
almost the same level at the
base of the stem.
 Tuberous or tubercular
root:
 Here, the modified
adventitious root is swollen
without any definite shape. It
is always produced singly
and not in clusters.
 e.g., Ipomoea batotas
(Sweet potato)

29.  Nodulose roots e.g., Curcuma amada, (mango ginger)Here, the root
becomes swollen at its tip.
 Moniliform roots e.g., Momordica. Here, the roots show beadlike
swellings at frequent intervals.
 Annulated roots E.g., Ipecac. Here, the adventitious roots have a
series of ringlike swellings on their surface.

30. Aerial Root Modifications
 Aerial roots are adventitious roots which
develop from the aerial parts of the plant to
perform various functions.
 For Mechanical Support
 For Vital Functions

31. For Mechanical Support
 Prop roots : e.g., Ficus benghalensis
(Banyan): In banyan the adventitious roots
arise fromthe horizontal branches and
grow vertically downwards.
 After reaching the soil they become thick
and woody.
 Thus, they function as pillars giving
mechanical support to the branches.
 Hence, they are also known as
columnar roots.
 Stilt roots : e.g. Pandanus : In Pandanus
the adventitious roots arise from the lower
part of the main stem and grow obliquely
towards the soil.
 They serve to keep the plant erect by
giving additional support.

32.  Climbing roots: e.g., Piper betel, : These roots
arise from the nodes and help in attaching the
climbing stem firmly to a support like a tree or a
wall, by various mechanisms.

33. Haustoria or sucking roots
 e.g. Cuscuta : Parasites like
Cuscuta develop a kind of root
which penetrates into the tissue
of the host plant and help to
draw nutrients from the host by
sucking it.
 The parasitic plants are not
completely equipped to prepare
their food.
 Hence, such plants have to
depend on host plants for
nutrients.

34. Floating roots
 In Jussiea which is an aquatic plant, special
spongy roots called floating or respiratory
roots arise from the plant.
 They are adventitious and enclose a tissue
called aerenchyma.
 These roots usually develop above the level
of water and serve to store up air and help
in buoyancy of the plant.
 In addition, the floating roots may also
perform the respiratory function.

35. Epiphytic roots
 e.g., Vanda:
 In epiphytes like orchids which grow on other plants, special
adventitious roots called epiphytic roots are produced.
 The outer region of the root is made up of a special tissue called
the velamen.
 This tissue absorbs moisture from the air and makes it available
to the plant.
 These roots do not penetrate the host tissue like parasitic roots