Vegetative Morphology of Root , Stem and Leaf

Introduction :

Angiospermic or flowering plants show a great variety of shape, size and form. The size ranges from the minute Wolffia and Lamna (0.1cm) to the tall Eucalyptus (up to 100 metre) and large sized Banyan (Ficus bengalensis). In habit, they range from herbs and shrubs to trees.

Morphology (Gr. Morphos = Form; logos = Study) is the branch of science which deals with the study of form and structure. In botany, it generally means the study of external features, forms and relative positions of different organs on plants.

Morphology (Gr. Morphos = Form; logos = Study) is the branch of science which deals with the study of form and structure.

Parts of a flowering plant :

Flowering plants consist of a long cylindrical axis which is differentiated into underground root system and an aerial shoot system.

The root system consists of root and its lateral branches. The shoot system has a stem, a system of branches and leaves. The different parts of a plant are called organs.

Organs are differentiated into two types, vegetative and reproductive.

Vegetative organs take part in nourishing and fixing the plant, viz., root, stem, leaves.

Reproductive organs are required in multiplication. They comprise flowers, fruits and seeds (formed inside fruits).

Organs similar in basic internal structure and origin which may appear different and perform different functions are called homologous organs. The relationship amongst these organs is called homology.

Organs performing a similar function or having a similar external form but different internal structure and origin are termed as analogous organs. The relationship in analogous organs is called anology.

ROOT

The root is usually an underground part of the plant which helps in fixation and absorption of water. The root with its branches is known as the root system.

Radicle comes out / arise from the seed coat in the form of soft structure and move toward the soil. it develops and forms primary root.

Characteristics of the root

(i) The root is the descending portion of the plant axis and is positively geotropic.

(ii) It is non-green or brown in colour.

(iii) The root is not differentiated into nodes and internodes.

(iv) As a rule the root does not bear leaves and true buds.

(v) Usually the root tip is protected by a root cap.

(vi) The root bears unicellular root hairs.

(vii) Lateral roots arise from the root which are endogenous in origin (arises from pericycle)

Parts of the root :

(i) Region of cell division : The tip of the root is called calyptra or root cap. It is for protection of root tip against any injury. It is formed from meristem called calyptrogen. Pandanus is the only plant with multiple root caps. In the aquatic plants like Pistia, Lemma and Eicchornia instead of root caps, they have root pockets for buoyancy. The root caps are absent in parasites and mycorrhizal roots.

(ii) Region of cell elongation : The region of cell division lies partly within and partly beyond the root cap. This is the meristematic region of the root which produces new cells by cell division.

(iii) Region of maturation : This region is present above the region of elongation. In this region the epidermal cells produce many tubular, unicellular outgrowths called root hairs. This is also called Piliferous region. Water absorption mostly takes place through this region. The root hairs are absent in many aquatic plants

(iv) Region of maturation : Above the root hair zone, mature region is present. This region consists of permanent cells. Lateral roots are produced endogenously from the mature region. Conduction of water and mineral salts takes place through this region.

TYPES OF ROOT SYSTEM

Roots are of two types:

1.   Tap root system                                            

2.   Adventitious root system

(i) Tap root system :

The tap root system develops from radicle of the germinating seed. It is also called the normal root system. The radicle develops into a primary root which grows vertically downwards and become the tap root. The tap root is the true root that produces many lateral roots endogenously which grow obliquely. The tap root system is present in dicotyledonous plants.

(ii) Adventitious root system :

The root system that develops from any part of the plant body other than the radicle is called the adventitious root system. It is mostly seen in monocotyledonous plants. In grasses, fibrous root system is present. It is a type of adventitious root system. In this case the primary root formed from the radicle disappear soon. Then many slender roots develop from the base of the stem as cluster of fibres, hence called the fibrous root system. Shrub like monocots needs additional support because of the adventitious root. e.g., Stilt root in sugarcane.

Modification of tap roots

(i) Storage roots : In some plants, the primary tap roots are modified for storing reserve food materials. The secondary roots remain thin and they are absorptive in function.

The storage roots are usually swollen with various forms are as follows

(i)  Conical roots – These roots are thicker at their upper side and tapering at basal end eg. Carrot

Carrot

(ii) Fusiform roots – These root are thicker in the middle and tapering on both ends. In this type of roots both hypocotyl and root help in storage of food. Eg. :- Radish

Radish

(iii) Napiform – These roots become swollen and spherical at upper end and tapering like a thread at their lower end. Eg. Turnip (Brassica rapa), Sugarbeet

Sugarbeet

(iv) Tuberous root – Such roots do not have regular shape and get swollen & fleshy at any portion of roots. Eg. Mirabilis.

Mirabilis

Branched Roots

(i) Nodulated root – Nodules are formed on branches of roots by nitrogen fixing bacteria. (Rhizobium) . Eg. Plants of leguminosae family (Papilionatae) – Pea

Pea

(ii) Pneumatophores or Respiratory roots :

Ceriops

The plants which grow in marshy areas, scarcity of oxygen is found. the plants, which grow where in this region some branches of tap root grow vertically upward and comes on surface of soil. These roots are called pneumatophores have minute pores called pneumathodes or lenticels by which air entered in side the plant and get oxygen for respiration

e.g., Sonneratia, Heritiera, Rhizophora, Avicennia and Ceriops etc. and are found in sundarbans of West Bengal

Modification of adventitious roots

For physiological or Vital functions

(a) Storage roots :

The roots where adventitious roots become swollen to store food. They are following types :

Tuberous roots : These adventitious roots are swollen without any definite shape e.g., Ipomoea batata or (sweet potato).

Ipomoea batata

Fasciculated roots : These are tuberous roots arising in cluster from the base of the stem. e.g., Dahlia, Ruellia (Menow weed), Asparagus (Asparagus fern) etc.

Dahlia

Nodulose roots : These roots become swollen at their tips due to accumulation of food e.g., Maranta sp. (Arrowroot), Curcuma amanda (Mango – ginger).

Curcuma amanda

Moniliform or Beaded roots : These adventitious roots are swollen at frequent intervals. This gives the root a beaded appearance. e.g., Portulaca (Rose moss) Momordica (Bitter gourd) Cyperus (Guinea rush).

Momordica

Palmate tuberous roots : In Orchis there is a pair of succulent tuberous root, one of which perishes every year while another new one is formed by its side. Such orchid roots may sometimes be of palmate shape, therefore, called palmate roots.

Orchis

Annulated roots : The roots of a medicinal plant, Ipecac (Cephaelis ipecacuanha) yields emetine that looks like discs placed one above another, therefore, called annulated.

Cephaelis ipecacuanha

(b) Epiphytic roots : These roots are also called ‘hygroscopic roots’. These roots develop in some orchids which grow as epiphytes upon the trunks or branches of trees. They hang freely in the air and absorb moisture with the help of special sponge like tissue called velamen. Velamen is modification of epidermis. e.g., Venda, Dendrobium etc.

(c) Parasitic or Haustorial roots : Plants which depend on plant partially or totally for their food material are known as parasites. The roots of parasitic plants, which penetrate into the host tissues to absorb nourishment, are called haustorial roots. The haustorial roots of Cuscuta (Dodder, vern. Amarbel) penetrates the host upto phloem and xylem to absorb organic food, water and minerals. The haustorial roots of partial parasite – Viscum (Mistletoe) penetrate upto xylem of host to absorb water and minerals.

Parasite which absorb their nutrients from the host stem are known as stem parasites while those which absorb their nutrients from the host root are know as root parasite.

(d) Saprophytic roots : They are also called mycorrhizal roots as here roots are associated with fungal hyphae either superficially (ectomycorrhizae) or internally (endomycorrhizae) for absorption of water and minerals. e.g., Monotropa and Sarcodes.

(e) Photosynthetic or Assimilatory roots : These are green, aerial, adventitious roots which prepare food materials by photosynthesis are called photosynthetic roots or assimilatory roots e.g., Taeniophyllum, Trapa and Tinospora. In some epiphytes like Taeniophyllum, the stem and leaves are absent. The entire plant is represented by thin green, ribbon like roots which contain velamen. These roots absorb moisture from the atmosphere and manufacture food materials by photosynthesis. Since the roots are green and perform photosynthetic activity, these roots are called photosynthetic roots or assimilatory roots.

(f) Reproductive roots : Some fleshy adventitious root develop buds which can grow in to new plants. These are called reproductive root. These roots serve as means of vegetative propagation. e.g., Sweet potato, Dahlia etc.

(ii) For mechanical function

(a) Stilt roots : The aerial, adventitious obliquely growing roots that develop from the lower nodes of the stem to give additional support are called stilt roots. This roots bear several large overlapping root caps called multiple root caps. e.g., Sugarcane, Pandanus, Rhizophora, Sorghum and Maize. Pandanus (screw pine) is a common sea shore plant.

They also help in the absorption of water and minerals from the soil. In monocots, these roots arise in whorls from a few basal nodes of stem.

Pandanus

(b) Prop roots : These adventitious aerial roots arise from horizontal aerial branches of the trees like Ficus bengalensis  (Banyan). Initially, they are hygroscopic in function, become red in moist condition and possess root-caps at their apieces. They grow vertically downward, penetrate the soil, become thick and assume the shapes of pillars. They provide support to the spreading branches of tree. Sometimes the main trunk dies and it is replaced by prop roots which assume the shapes of trunks.

In India, the biggest banyan tree having large number of prop roots are found at Indian Botanical Gardens, Kolkata and Kadiri (Andhra Pradesh).

Ficus bengalensis

(c) Buttress roots : The horizontal plank like aerial, adventitious roots that develop at the base of the stem to give additional support are called buttress roots or ballast roots, e.g., Terminalia and Salmalia. In some huge and heavy trees, plank like roots develop at the base of the stem on the soil surface. These roots give additional support and act like ballasts. Hence these roots are called ballast roots.

Terminalia

(d) Climbing roots : The aerial adventitious roots that arise from the nodes or internodes of weak stemmed plants to climb up their support are called climbing roots, e.g., Pothos, Piper betel, Vanilla and Hedera. Many weak stemmed plants climb up their supports in order to expose their leaves efficiently to sunlight. In Pothos and Hedera, climbing roots develop all over the stem. In Vanilla, single tendril like root arise at each node. Hence they are called tendrillar roots. In Piper betel, many short branched, adventitious roots arise at each node. These roots are called clinging roots.

Pothos

(e) Floating roots : These roots develop from the nodes of floating aquatic plants like Jussiaea (=Ludwigia). They store air, become inflated and spongy, project above the level of water, make the plant light and function as floats.

Jussiaea

(f) Contractile or Pull roots : Some roots of plants with underground stems contract or swell so that the aerial shoots are kept in a proper depth in the soil. These roots are called contractile or pull roots, e.g., Canna, Crocus, Allium, Lilium, Freesia, etc.

Onion

(g) Root thorns : In aroids like Pothos and many palms (Acanthorhiza and Iriartea) the adventitious roots become hard and pointed hence called root thorns.

Acanthorhiza

stem

The stem develop from the plumule of the germinating seed. Normally it is the aerial part of the plant body. The stem with it's branches, leaves, buds, flower and appandages is known as shoot system.

The stem shows the differentiation of nodes and internodes. The place where the leaf develops on the stem is called the node. The portion of the stem between two successive nodes is called the internode.

Characteristics of stem

(i) Stem is an ascending axis of the plant and develops from the plumule and epicotyl of the embryo.

(ii) It is generally erect and grows away from the soil towards light. Therefore, it is negatively geotropic and positively phototropic.

(iii) The growing apex of stem bears a terminal bud for growth in length.

(iv) In flowering plants, stem is differentiated into nodes and internodes. A node occurs where leaves are attached to the stem. Internode is the portion of stem between the two nodes.

(v) The lateral organs of stem (i.e., leaves and branches) are exogenous in origin (from cortical region).

(vi) The young stem is green and photosynthetic.

(vii) Hair, if present, are generally multicellular.

(viii) In mature plants, stem and its branches bear flowers and fruits.

Diverse forms of stem

Caudex: It is unbranched, erect, cylindrical stout stem and marked with scars of fallen leaves as in palms. Eg: - Palm.

Palm

Culm: - Stem is jointed with solid nodes & hollow internodes. Eg:- Bamboo (Gramineae).

Bamboo

Scape:- In some monocotyledons there is no aerial stem instead there are aerial shoot (Branch) which bear flowers. Eg:- Onion and aroids

Onion

Prostrate or procumbent:- If the stem trails on the ground and lie prostrate. Eg:- Evolvulus and oxalis

oxalis

Decumbent:- Stem trails for some distance and then tends to rise at its apex. Eg:- Tridax, Portulaca

Tridax

Diffuse:- When the branches of the stem are spread out in all directions on the ground. Eg:- Euphorbia, Boerhaavia

Euphorbia

Climbers:- Stem which attach themselves to nearby object by means of some special devices like hooks. Eg. Bougainvillea (by hook), wild pea (by tendrils)

Bougainvillea

Modification of stem :-

Sub-aerial modification

Runner – When stem grows and spread on the surface of soil. Roots are developed at lower side and leaves from upper side from node Eg. Cynodon  dactylon (Doob grass).

Cynodon  dactylon

Stolon – In it branches are small and stem condensed and grow in all direction. After sometime, of growing their apical region comes out from the soil. Eg. Fragaria (Wild strawberry), Jasmine Peppermint

Fragaria (Wild strawberry)

Sucker – In it the main stem grow in the soil but branches develop from nodes above the soil. Eg. Mint, Pineapple, Chrysanthemum.

Pineapple

Offset – Generally these are aquatic plants which have fragile stem. Eg. Pistia, Eichhornia

Underground modification

This type of modification occurs generally for food storage and vegetative propagation.

Sucker - This is a sub aerial branch that arises from the main stem. Initially it grows horizontally below the soil surface and later grows obliquely upward. They are shorter and stouter than the runners. e.g., Mentha arvensis (mint vern. Podina) and Chrysanthemum

Mentha arvensis

Rhizome – It is fleshy and horizontally found below in soil small nodes and internodes are found which are covered by scaly leaves. Eg. Ginger, Turmeric

Ginger

Corm – It is condensed structure which grow vertically under the soil surface. Eg. Colocasia, Alocasia, Zaminkand.

Colocasia

Tuber – The tips of branches become swollen in the soil. Eyes are found on them which are axillary buds and covered with scaly leaves. Eg. Potato

Potato

Bulb – This stem has disc like structure and surrounds with numerous fleshy scaly leaves. Many roots arise from its base. Eg. Onion, Garlic.

Onion

Aerial stem modification

Stem tendril – In this type axillary tendril in place branches and helps in climbing of those plants which have weak stem. Eg. Grapes, Passiflora, Cucumber, Pumpkins, Watermelon

Grapes

Phylloclade -  Stem is modified into a flat, fleshy and green leaf like structure and carries out photosynthesis like leaf. The leaves are modified into spines Eg. Opuntia, Euphorbia

Euphorbia

Prickle and hooks -  These developed only from cortex and epidermis and found at nodes or internodes. it helps in climbing. It is exogenous in origin. Eg. Rose, Smilax

Rose

Stem thorn/Thorn -   It is developed from axillary bud or terminal bud of the stem. It may bear leaves, flowers. It is endogenous in origin Eg. Carissa (Karonda),Bougaivillea, Pomegranate, Citrus

Pomegranate

LEAF

The leaves develop from the nodes. Their main function is photosynthesis and food making axillary buds are found in its axil.

Leaf is divided into 3 main parts:-

Leaf base – The part of leaf attached to stem

Petiole – The part of leaf connecting the lamina with the branch or stem, petiolated or stalked leaves are known as petiolate and when petiole or stalk is absent then leaves are called sessile.

Lamina – It is a broad and flattened part of leaf. Its main functions are photosynthesis and transpiration.

Stipules:-

Leaves of some plants have lateral appendages on either side of leaf base, known as stipules. If stipules are present in leaf it is called stipulated. Leaf, if it is absent then leaf is called Ex-stipulated.

Stipules are of various types –

Free lateral - They are independently present on both sides of leaf base Eg. Hibiscus rosasinensis (China rose).

Interpetioler – When two leaves are meet oppositely at the node then nearest stipules of each leaf joint with each other. In this way only two stipules of two leaves are found in place of four Eg. Ikora.

Intrapetioler - In this type both stipules of a single leaf join with each other to form a single stipule.  Eg: - Gardenia

Foliaceous – These type of stipules form a leaf like structure. Eg. :- PeaScaly - Stipules are dry, small and paper like. Eg :- Desmodium

Spiny – Stipules modified into spiny. Eg. Zizyphus (Ber)

Ochreate – When both stipules of leaf combine together and form a tube like structure, it is called Ochreate. Eg. Polygonum

Adnate – Both stipules are joint with petiole. Eg. Rose.

Tendrillar - Stipules are modified into tendrils like structure. Eg. Smilax

Types of Leaves –

Foliage leaf – They are usually green Coloured and their main function is photosynthesis.

Cotyledonary leaf – This leaf comes out during germination and helps in nutrition until the leaf is not formed.

Scale leaf – Such leaves are usually dry membrane like and they cannot perform photosynthesis.

Bract – Bract are the leaves which contain flower in their axil.

Bracteole – These are leaf like structure found on pedicel.

Floral leaf – Sepals, petals, stamen and carpel are found in flower which are included in this type of leaf.

Note: Perianth: In some flowers, Calyx and Corolla are not distinct and are termed as Perianth, and unit of perianth is called tepal. Eg. Lily

Duration of Leaf:

Persistent/Evergreen – Leaves of such plants are found in all season and do not (fall) shed combindly. Eg.  Pine,  Saraca indica, Datepalm.

Deciduous – All leaves of such plants shed at the same time Eg. Azadirachta, Ficus

Caducous – Leaves are shed as the bud formation takes place. Eg :- Rose

NOTE:

Cauline leaves – When the leaves are found on node of stem, then these are called cauline leaves.

Ramal leaves – When leaves are found on branches, then these are called ramal leaves.

Radical leaves – During favourable season, leaves develop from the nodes of under ground stem and seem that they are developing from roots. This type of leaves are known as radical leaves.

VENATION OF LAMINA

The arrangement of veins and veinlets in leaves (Lamina) is known as venation. It is of 2 – types

(a)  Reticulate: It is found in dicots. Exception – Calophyllum (It has parallel venation)

(b)  Parallel: It is found in monocots. Exception – Smilax (It has reticulate venation)

Reticulate venation – In it many veins divided into various branches (veinlets) and form a net like structure.

Reticulate venation is of 2 – types –

(i)        Unicostate or pinnate – In this type of venation having only one principal vein or midrib that give off many lateral veins which proceed toward margin and apex of lamina of the leaf and form a network.Eg. :- Mango, Guava, Peepal.

(ii)       Multicostate or palmate – In this type of venati0on many principal veins arising from the tip of petiole and proceed upward this is again two types -

(a)       Multicostate divergent – Many principal veins arising from the tip of petiole diverge from the toward the margin of leaf blade Eg. Cotton, Castor, Cucurbita.

(b)       Multicostate convergent – Many principal veins arising from the tip of petiole. At the base of leaf they are closely arranged but diverge from are another in middle part and converge towards the apex of leaf.Eg. :- Camphor, Zizyphus, Tejpat, Chinarose, plum.

Parallel venation - In this type of venation, all veins run parallel to each other and they do not form network,

They are of 2 types –

(i) Unicostate or pinnate : This type of pattern having only one principal vein, that gives off many lateral veins, which proceed toward the margin of leaf blade in a parallel in manner but they donot have veinlets. Eg. Banana, Ginger, Canna

(ii) Multicostate or palmate: Having many principal veins arising from the tip of the petiole and proceeding upwards.

(a)  Multicostate  convergent : Many principal veins arising from the tip of petiole and diverge toward the margin of leaf. They donot divide into veinlets and do not form network.

Eg. : - Coconut, Date palm.

(b)  Multicostate convergent: Many principal veins arising from the tip of petiole run in a curved manner in lamina and converge towards the apex of leaf blades.

Eg: - Wheat, grass, sugar-cane, Bamboo

Modification  of leaves –

When leaf is modified in different structure. It is called modification of leaves.

(1)       Leaf tendril – In it, whole leaf is modified in to a wire like structure which is called leaf tendril Eg. Lathyrus aphaca (wild pea)

(2)       Leaf  spine - Leaves or any part of leaflet are modified into pointed spine. Eg. Opuntia, Aloe, Argemone.

(3)       Leaf scale – In it leaves become thin, dry and form a membrane or paper like structure and serve to protect axillary buds as in Ficus and Tamarix, Ruscus or store food and water as in onion.

(4)       Leaf pitcher – Leaves of some plants are modified to pitcher shape. Eg. Nepenthes, Dischidia

(5)       Leaf bladder – In some plant, leaves are modified into bladder like structure Eg. Utricularia

(6)       Leaf Hooks – In some plants terminal leaf lets are modified into curved hooks for helping the plant in climbing. Eg. Argemone, Opuntia, Alone.

(7)       Phyllode – In it petiole becomes flat structure and function as normal as normal leaf. Eg. Australian acacia

(8)       Leaflet tendril – When leafleat is modified into tendril like structure than it is called leaflet tendril. Eg. :- Pisum sativum (Garden Pea), Lathyrus odoratus (sweet pea).

Note : Dionaea (Venus flytrap) is insectivorous plant and they also have

modified leaves.

Simple and Compound Leaf

(1)       Simple Leaf: A leaf which may be incised to any depth, but not down to the midrib or petiole then this type of leaf called simple leaf.

(2)       Compound leaf: A leaf in which the leaf blade is incised up to the midrib or petiole, thus dividing it into several small parts, known as leaf lets.

It has two types:-

(A)       Pinnately compound leaf: In this type of leaf mid rib is known as rachis. Leaf are arranged on both sides of rachis. Eg. Neem

It is of two types

(i) Unipinnate: In this type of leaf divison occurs only once and leaf lets are directly attached on both sides of rachis. If the number of leaflet is even leaf is known as paripinnate. Eg. : Cassia fistula, Sesbania

If the number of leaflet is odd, it is known as imparipinnate. Eg. :- Rose, Neem

(ii) Bipinnte: A twice pinnate compound leaf. Eg. :- Acacia, Gulmohar, Mimosa

(iii) Tripinnate: A thrice pinnate compound leaf. Eg. Moringa

(iv) Decompound: A compound leaf, which is more than thrice pinnate. Eg: - Carrot, Coriander

(B)      Palmate compounds: In this type incision of leaf are directed from leaf margin to apex of petiole and all leaflets are attached on the upper end of petiole. Eg. Silkcotton.

It is of following types :

(i) Unifoliate: When single leaf let is found. Eg. :- Lemon

(ii) Bifoliate: When two leaf lets are present. Eg. :- Bauhinia, Regnelidium

(iii) Trifoliate: When three leaf lets are attached. Eg. :- Oxalis, Aegle.

(iv) Tetrafoliate: When four leaf lets are attached to the petiole. Eg. :- Marsilea

(v) Multifoliate: When more than four leaflet are found, then leaf is called multifoliate palmate compound leaf. Eg. Silkcotton.

Shape of lamina:

1.         Acicular: - Lamina is long and pointed. Like a needle. Eg. Pine.

2.         Lanceolate: - In this type lamina is pointed or narrower at the ends while broader in the middle. Eg. Bamboo, Nerium

3.         Linear: - The lamina is long and narrow having parallel margins. Eg. Grass

4.         Ovate: - In this type lamina is egg-shaped having broad base with slight narrow top. Eg. Ocimum, Banyan, China rose

5.         Cordate: - Its shape is like a heart. Eg. Betel.

6.         Oblong: - Long and broad lamina. Eg. Banana.

7.         Sagittate: - The lamina is triangular in shape. Eg. Sagittaria.

8.         Spathulate: - Thelamina is broad spoon shaped. Eg. Calendula.

9.         Orbicular or Rotund: - In this type the lamina is spherical. Eg. Lotus.

10.      Elliptical or Oval: In this type the middle part of lamina is broad while the ends are narrow and oval. Eg. Guava, Jamun

11.      Oblique: - In this type midrib divides, lamina into two unequal halves. Eg. Begonia, Neem.