Plant Morphology

By

Jacob Thomas

Plants have three basic organs: roots, stems, and leaves

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

ROOT

• Root is a non-green, underground, descending portion of the plant axis

• Develops from radicle

Characteristics of root

i. Descending part

ii. Negatively phototrophic

iii.Non-green

iv.Root cap /root pockets

v. Unicellular root hair

vi.No nodes

vii.Lateral roots Endogenously

Regions of typical roota) Root cap – mucigel to

lubricate

b) Zone of cell division

c) Zone of elongation

d) Zone of root hair or

absorption

e) Zone of maturation or

differentiation

Functions of root

a) Anchorage

b)Absorption

c) Conduction of water

& minerals

d)Transport of nutrients

Types of root system1. Tap root system Roots develops, usually from the radicle of an embryo of seed is called tap root & the system is called tap root system.

2. Fibrous Root SystemThe roots which develop from any other part of the plant except the radicle is called adventitious root and this system is called adventitious or fibrous root system.

eg. Monocot plants

Tap root systemFibrous root System

Modifications of root for storage

a) Conical roots

eg. Carrot

(Daucus carota)

Modifications of root for storage

b) Fusiform roots

eg. Radish

(Raphanus sativus)

Modifications of root for storage

c) Napiform roots

eg. Beet

(Beta vulgaris)

Modifications of root for mechanical support

1. Epiphytic rootsclinging roots

Hanging roots -

velamen tissue

Absorbing roots

eg. Orchids

Modifications of root for mechanical support

1. Stilt roots

eg. Maize,

Jowar,

Sugarcane

Modifications of root for Physiological functions

1. Pneumatophores

or

Breathing roots

eg. Avicennia,

Rhizophora,

Sonneratia

Modifications of root for Physiological functions

1. Parasitic roots /

Haustoria / Sucking

roots

eg. Total parasite – Cuscuta

Partial - Loranthus

StemStem is the

ascending axis

of a plant and

develops from

the plumule and

epicotyle of the

embryo

Node

InternodeShoot

system

Characteristics of stem

Terminal bud for growthAscending axisDeveloping from plumule &

epicotylePhototrophicNodes & internodesBranches & leaves

exogenousMulticellular hairBears flowers & fruits

BUDS

Young underdeveloped shoot consisting of a shoot apex, compressed axis and a number of tender leaves arching over the growing apex

BUDS

Vegetative buds

Grow to only leafy shoot

BUDS

Mixed Buds

Produce both vegetative &

floral branches

Apical bud

Borne at the apex of main

branch

Axillary Bud

Occur in theaxis of

leaf

Modifications of stem

The structural and functional change in the normal form and structure of the stem due to change in normal function

of the stem is called modification of the

stem

1. Underground stem Modifications

Herbaceous plants to overcome

unfavorable season

Examples

RhizomePerennial stem of the plant grows below soil

surface.Fleshy due to storage of foodNodes, internodes, scaly leaves, axillary buds,

& adventitious roots

Straggling rhizome

Root stock

Bulb Stem underground,

disc like, small & modified and reduced

Convex / conical , compressed internodes

Nodes bear fleshy scales

Leaves in concentric Axillary buds Adventitious roots

Bulb

Tunicated bulb

(scaly leaves covering fleshy leaves in

concentric)

Scaly or naked bulb

No covering / overlap one another

Tulip

Tuber

The tuber stores starch as reserve food material

Corm

Fleshy underground round stem

Buds at nodesAdventitious rootsFood storage

2. Sub-aerial modifications

Delicate stem unable to stand erect

A. Runner

Oxalis OxalisDoob grass

2. Sub-aerial modifications

B. Stolon

FernNepenthes

3. Aerial modificationA. Tendril

weak stem Requires support Axillary buds

spring like tendrils

Sensitive to touch Coil around Support to climb

up Expose leaves to

sunlightPassiflora

GrapesApical bud tendrilCucumberExtra axillary bud

3. Aerial modificationB. Thorn

Xerophytic plants Vascular

connections with stem

Axillary branches hard sharp pointed thorns

Protects from animals

Reduces transpiration & desiccation

Citrus DurantaBougainvillea

3. Aerial modificationC. Phylloclade

Xerophytic plants Leaves stem flat green

phylloclade Check the rate of

transpiration

Opuntia

3. Aerial modificationD. Cladode

Xerophytic plants

Modification of stem & branches of limited growth

Phylloclade with one or two internodes Cladode

Asparagus Asparagus needle like, slightly flattened, green,

appear in clusters in the axil of a scaly leaf Ruscus looks like leaf. Develops from axil of a scaly

leaf. Bearing floral bud

3. Aerial modificationE. Bulbil Axillary Bud / vegetative bud large & fleshy due to

storage of food

Helps in vegetative ReproductionDioscorea

AgaveAllium

Functions

Primary

Bears & Holds

Conduction

Lateral growth

Flowers

Fruits & seeds

Secondary

Perennation

Vegetative propagation

Helps in photosynthesis

Check transpiration

Climbing

Leaf Structure

• A leaf is held away from its stem by a stem-like appendage called a petiole.

• The base of the petiole is attached to the stem at a node.

• The blade is the expanded thin structure on either side of the midrib and is usually the largest, most conspicuous part of a leaf

Leaf Parts

• The cuticle is part of the epidermis

• It produces a waxy layer called cutin, which protects the leaf from dehydration and disease.

• On the top and bottom is a layer of thick, tough cells called the epidermis. Its primary function is to protect the other layers of leaf tissue.

Leaf Parts Continued • Special epidermal cells called

guard cells open and close in response to environmental stimuli, such as changes in weather and light.

• They regulate the passage of water, oxygen, and carbon dioxide into and out of the leaf through tiny openings called stomata.

• Located between the upper and lower epidermis is the mesophyll.

• Located within the mesophyll cells are chloroplasts, where photosynthesis takes place.

BUDS o A bud is an undeveloped shoot

from which embryonic leaves or flower parts arise

o A leaf bud is composed of a short stem with embryonic leaves

o A flower bud is composed of a short stem with embryonic flower parts.

o Buds are named for the location they inhabit on the stem surface.

o Enlarged buds or parts of buds form the edible portion of some horticultural crops