Study Notes on Morphology of Flowering Plants

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INTRODUCTION


  • You know that flowering plants are multicellular organism.
  • They grow by cell division and their morphological features and traits are genetically determined.

  • Even through the angiosperms show such a large diversity in external structure they are all characteristics of presence of roots, stem, leaves, Flowers and fruits.
  • Morphology deals with the study of forms and features of different plant organs like roots, stem, leaves, flower, seeds fruits etc.
  • Morphology play a key role in the classification of angiosperm. In this unit you will learn about the important morphological features of the flowering plants.
  • We shall learn how to describe a flowering plant, using examples are modified to serve specific needs including defence from their enemies.
  • You will get some idea of the economic importance of selected plant families.

THE ROOT


  • Roots are cylindrical, underground and non-green part of the plants. It is generally the descending portion of the plants axis I.e., it grows downwards into the soil.
  • It lacks nodes, leaves buds but gives rise to endogenous lateral branches. Roots move in the direction of gravity (geotropism) and against the direction of light (phototropism).
  • Hence, the roots are said to be positively geotropic and negative phototrophic Plants have well developed root systems.
  • The main roots and it’s lateral form the root system. There are three types of root system.

TAP ROOT SYSTEM

The primary root is directly elongated from the radicle and grow inside the soil. (E.g. Dicots).

  • It lateral roots of several orders that are referred to as secondary, tertiary roots etc.
  • The primary and its branches constitute the tap root system.

FIBROUS ROOT SYSTEM

  • In monocotyledonous plants, the primary root is short-lived and is generally replaced by number of find fibrous roots.
  1. These roots originate from base of the stem and constitute the fibrous toots system ad seen in wheat plant.

ADVENTITIOUS ROOT SYSTEM

  • Some plants have specialised roots called adventitious roots. These roots develop from any parts of the plant other than the radicle e.g. Grass, Monsters Banyan tree.

MAIN FUNCTION OF ROOTS

  • Absorption of water and minerals from the soil.
  • Provide Anchorage to the plants parts.
  • Storage of reserve food material.
  • Synthesis of plant growth regulators.

REGIONS OF THE ROOT

  • ROOT CAP-The apex of the root is covered by a thimble-like, structure called root cap, it is multicellular and is made up of parenchymatous cells.
  • REGION OF MERISTEMATIC ACTIVITY- This layer is few millimeter above the root cap, the cell of this layer are thin walled, small, with sense protoplasm.
  • REGION OF ELONGATION-The cell proximal to the meristematic region undergo rapid elongation and enlargement and are responsible for the growth of roots in length.
  • REGION OF MATURATION- The cells elongation zone gradually differentiate and mature. Hence, this zone proximal to region of elongation is called the region of maturation.

MODIFICATION OF ROOTS

  • The roots are mainly involved in absorption of water and minerals from the soil.
  • Roots in some plants undergo modification in their shape and structure in order to perform function like respiration, storage and protection.
  1. STORAGE ROOTS- In some plants the primary tap roots is modified to store food and assumes various shapes e.g. tap root of carrot, turnip, radish, beet and adventitious roots of sweet potato get swollen and store foods.
  2. RESPIRATORY ROOTS- In some plants such as Rhizopus growing in swampy areas, many roots come out of the ground vertically upwards to get oxygen for respiration. Such roots are called pneumatophores.
  3. PROP ROOTS- They Aries from the branches of stem for providing mechanical support to heavy branches, as pillars e.g. banyan trees.
  4. STILT ROOTS- They Aries from lower nodes of stem to support main axis and enter the soil obliquely e.g. sugarcane, maize.

STEM


  • The plantsaxis that bears buds and shoots with leaves  and, at its basal end, roots.
  • The stem conducts water, minerals, and food to other parts of the plant.
  • it may also store food, and green stems themselves produce food.
  • The region bearing leaves present at regular intervals on the stem and it’s branches are called nodes.
  • the part of stem present between the two nodes are called internodes.
  • A bud is defined as the young immature, under developed, compact shoot.
  1. TERMINAL BUD- The bud present at the tip of the stem is called terminal bud.
  2.  AXILLARY BUD- The leaf makes an angle with the upper part of the stem, the angle made between the leaves and upper part of the stem is called the axil.

FUNCTION OF THE STEM

  • Stem bears and supports leaves, flower and fruits.
  • It conduct water and minerals salts from roots to leaves and fruits.
  • The food manufactured in the leaves transported to the roots , fruits and organs of storage through the stem.

MODIFICATION OF STEM

The stems of some plants in modified to perform different function in order to help to adapt to the present environmental condition.

  • Underground stem- Stem is generally the aerial part of the plant I.e. it is present above the ground but in some plants it is modified for storing food material.
  1. Rhizome- it grow parallel or horizontal to soil surface, ginger and turmeric.
  2. Tuber- it is terminal portion of underground stem branch which is swollen on account of food accumulation of food, Potato.
  3. Corm- It grows vertically beneath soil surface, colocasia, gladiolus and crocus.
  4. Bulb- Stem is reduced and disc shaped, onion lily garlic.

 

  • Stem tendrils- In some plants the axiliary bud present on the stem modify to form tendrils. These are long, thin, thread like spirally coiled sensitive structure. E.g. pumpkins watermelon cucumber.
  • Thorn- The axillary buds of plants like citrus and Bougainville lose their ability to grow and form hard woody ad pointed structure called thorns.

SUB AERIAL WEAK STEM

  • Offset- Aquatic plants such as pistia and Eichhormia contain a lateral branch which bear short internodes.
  • Sucker- In plants like banana, pineapple the lateral branches originate from the basal and underground portion of the main stem.
  • Runners- It is elongated, prostate branch with internodes and roots at nodes e.g. grasses.
  • Stolons- In plants like mint and Jasmine a slender branch arises from the base of the main axis.
  • Aerial stem- Plants present in arid modify their stem into flattened or fleshy, cylindrical structure called phylloclade. These structure carry out function of photosynthesis.

THE LEAF


  • A leaf is a lateral, generally flattened structure borne on the stem.
  • It develops at the node and bears a bud in its axil.
  • It originates from the shoot apical meristem and arranged in an acropetal order of the stem.

PARTS OF LEAF

  • A typical leaf consist of Three parts-
  • Leaf base– The lowest basal part of the leaf by which the leaf is attached to the node of the stems called leaf base.
  • The lead base may bear two lateral small leaf like structure called stipules.
  • The base swells and is called pulvinus.
  • Petiole- The cylindrical stalk that joints the leaf base with the leaf blade (lamina) is called Petiole.
  • Lamina and leaf blade- It green expanded part of the leaf, Blade is supported by the veins and veinlets.
  • the prominent vein present in the middle of the leaf blade is called midrib.

VENATION

The lamina of leaf blade contains veins and veinlets. The arrangement of veins and veinlets in the lamina or leaf blade is termed  as venation.

  • Reticulate venation- The veinlets form a network. It generally occurs in dicots such as peepal, hibiscus.
  • Parallel venation- The venation where the veins run parallel to each other within a lamian. It generally occurs in monocotes. E.g. banana.

TYPES OF LEAVES

Different types of leaves which exist in nature are:

Simple leaf- The leaf in which the leaf blade is not divided or when incised.

Compound leaf- The leaf in which the lamina or leaf blade is completely broken into distinct leaflets is called compound leaf.

  1. Pinnately compound leaf- In pinnately compound leaf, the midrib forms a common axis called rachis. E.g. neem.
  2. These are can be unipinnate, bipinnate, Tripinnate and decompound.
  3.  Palmately compound leaf- In palmately compound leaf, the leaflets are attached to a common point I.e. at the tip of the petiole. Eg silk cotton.
  4. These may be unifoliate, bifoliate, trifoliate, quadrifoliate and multifoliate.

PHYLOTAXY- The pattern in which the leaves arranged on the stem on its branches is called phyllotaxy.

  • Phyllotaxy is of three types these are following.
  • Alternative phyllotaxy- Single leaves present at each nodes in an alternate fashion eg sunflower.
  • Opposite phyllotaxy- A pair of leaves Aries at each nodes on opposite side eg Guava
  • Whorled phyllotaxy- In this phyllotaxy more than two leaves aries at each node in an whorled circle eg nerium.

MODIFICATION OF LEAVES

  • Leaves are generally responsible for the devlopment of plants body which process the phenomenon of photosynthesis, transpiration gaseous exchange etc.
  • At some times these condition are unfavourable, leaves get modify and perform other function such as storage, protection, defence, etc.
  1. Leaf tendrils- In some plants, leaves modify into long slendar, thread like, sensitive structure called tendrils. Eg, peas, sweat peas.
  2. Leaf spines- In some plants as aloe, cactus etc. leaves modify into small , sharp-pointed structures called leaf spines.
  3. Storage Organ- In some plans such as Onion garlic, etc. Fleshy leaves store food and hence forms the storage organ in plants.
  4. Phyllodes- In certain plants such as Australian Acacia the leaves are small and short lived.
  • These have green coloured leaves like structure which perform the function of photosynthesis These are know as phyllodes.

INFLORESENCES


  • These are the group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branch.
  • It is modified part of the shoot of seed plants where flowers are formed.
  • The modifications can involve the length and nature of the internodes and the phyllotaxis.
  • The variations in the proportions, swellings, adnationsconnations and reduction of main and secondary axes.

FUNCTIONS OF INFLORESCENCE

  • These are complex structures with many functions.
  • They are present in flowers in such a ways that allow for the transfer of pollen and optimization of the plant’s reproductive success.
  • They provide nutrition to the development of fruits and flower.

TYPES OF INFLORESCENCE

  • Raceme: The flowers are with pedicels of about the same length, which are attached along the elongate and unbranched peduncle of the inflorescence (eg: lily )
  • Panicle: The flowers are with pedicels, which are attached along the branches arising from the peduncle of the inflorescence (eg: oats, rice, fescue)
  • Corymb: The flowers are with pedicels of unequal length, which are attached along an unbranched, elongate peduncle, forming a flat-topped inflorescence (eg: hawthorns).
  • Umbel: The flowers are with pedicles, which are all attached at about the same point at the end of the peduncle this is specifically called a simple umbel (examples: onion,
  • Head: The flowers do not have pedicels, and they all cluster tightly on the expanded tip of the peduncle (eg-sunflower, daisy, marigold)
  • Cyme: The flowers with pedicels are located at the ends of the peduncle and lateral branches as well as along the length of the lateral branches
  • Catkin: The flowers have no pedicels, are unisexual, and are at tacked along the length of the peduncle (eg: hazelnut)
  • Spadix: The flowers have no pedicels and are attached along the length of the thickened or fleshy peduncle.

THE FLOWER


  • The flower is the reproductive unit in the angiosperm. It is a modified shoot meant for sexual reproduction.
  • It consist of four whorls which are successively arranged them on the thalamus or receptacle.
  • The four whorls present in a flower are calyx, corolla, androecium and gynoecium.

SYMMETRY OF FLOWER

  • The arrangement of the flower organs around the axis of a flower is know ad floral symmetry.
  • Actinomorphic flower (radial symmetry)- when a flower can be divided into two equal radial half 8n any radial plane passing through the centre eg- mustard.
  • Zygomorphic flower (bilateral symmetry)- When a flower can be divided into two similar halves only in one particular vertical plane. (eg-pea)
  • Asymmetric flower (irregular)- When flower cannot be divided into two similar half bay any vertical plane through the centre eg canna.

PARTS OF THE FLOWERS

  • Calyx- It is the outermost whorl of the flower and members are called sepals. Sepals are green leaf-like structure that protect the flower in the bud stage
  • Corolla- Corolla is the second whole of the flower. The individual leaf segment of the corolla is said to be petals, different shape of corolla are tubular, bell shaped, funnel shaped etc.
  • Androciem- It is a third whorl of Flowers Aries from inner wall of corolla, It is the male reproductive part which is composed of stamens.
  • A stamen consist of filament and anther, anther is usually bilobed.
  • Adhesion of stamens- The stamen attached to the other parts of floral organs such as petals, sepals, etc. When a stamen is attached to the petal, then it is called epipetalous.
  • Cohesion of stamens- The stamens may be free or united. When the stamen are free then they are called polyandrous and when stamen are united in a single bundle, then it is called monoadelphous.
  • Gynoecium- Gynoecium is a female reproductive part of the flower which is composed of one or more carpels. Carpels may be free or fused.
  • When carpels are free then they are said to be apocarpous eg- lotus and rose, and carpels are fused then they said to be synocarpous. Eg- mustard.
  • Carpel have three parts mainly-
  • Ovary- It is a basal and swollen part of the carpel. It is the lower part of the carpel which bears one or more ovules.
  • These ovules after fertilisation mature into seeds. The ovule attached with flattened cushion-like structure called placenta.
  • The ovary contain one chamber called unilocular, if two chamber called bilocular and if three it’s called trilocular.
  • Style- The Tube-like structure which connect the stigma to the overt is called style.
  • Stigma- Stigma is generally situated at the tip of the style, Stigma acts as the receptive organ for pollen grains during pollination.

PLACENTATION

An ovary have one or more then one placenta. The arrangement of ovules on placenta within the ovary.

  • The different types of placentation arrangement are marginal, axile, parietal, free central and basal.

THE FRUITS

The flowering plants or the angiosperms are characterised by the presence of a fruit. After fertilisation the ripened or mature ovary is called fruit.

PARTS OF FRUITS

A fruit mainly  consist of two parts namely fruits wall and seeds.

  • Fruit wall- Fruit wall or pericarp develops from wall of the ovary. It can be dry or fleshy.
  • If the pericarp is thick and fleshy it differentiates into three different layers namely.
  • Epicarp(outer cover), Mesocarp(middle layer), Endocarp(innermost layer).
  • If a fruit develop from ovary is called true fruit formation, and if it developed from other part of floral plant is called fasle fruits.

 

THE SEEDS

  • The ovules develop into seeds after fertilization. A seed is made up of a seed coat and an embryo..
  • The embryo is made up of an embryonal axis and one or two cotyledons.(as in gram and pea).
  • STRUCTURE OF DICOTYLEDONS SEED.
  • Seed coat- Outer protective covering of the seed is called seed coat,
  • which develop from integument of ovules.
  • The seed coat have two layer testa and tegman. Hilum is scar on seed coat through which developing seed were attached to the fruit.
  • Above the hilum small pore know as micropyle.
  • Embryo– Embryo is the most important part of the seed. Embryo consist of an embryonal axis and two cotyledons.
  • At the two end of embryonal axis are present the radicle and plamule.
  • Endosperm-  Endosperm is formed as a result of double fertilization. In some seeds such as castor it is a food storing tissue.


STRUCTURE OF MONOCOTYLEDONOUS SEED

  • In the seed of cereals such as maize the seed coat is membranous and generally fused with the fruit wall.
  • Below the grain covering are present two structure, endosperm and embryo .
  • The endosperm is bulky and stores food.
  • The outer covering of endosperm separate the embryo by a proteinous layer called aleurone layer.
  • Endosperm is consist of one large and shield shaped cotyledon known as scutellum and a short axis with a plumule and a radicle.
  •  The plumule and radicle are enclosed in sheaths which are called coleoptile and coleorrhiza respectively.

PERISPERMIC SEED

  • Mostly nucellus is consumed after fertilization due to absorption of food by the endosperm and embryo.
  • The nucellus remains persistent in the seed and is called
  • These seeds are called perispermic seed. Eg Piper nirgun.

REFERENCES

  1. https://ncert.nic.in/ncerts/l/kebo105.pdf