modifications of plant parts

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