Anatomy of Flowering Plants

Anatomy and functions

  • Anatomy of Dicot Root: Young dicot root has an optical growing point made up of primary permanent tissues. Which is cylindrical in outline and passes following tissue.
  • Epiblema / Piliferous layer / Rhizodermis: Consists of trichoblast that helps in absorption.
  • Cortex: Thin walled parenchymatous cells [rounded eg: Cicer / Singular Eg: Sunflower]. Which contain inter cellular spaces.
  • Endodermis: Biological checkpoint of cells because of presence of Casparian strips that is formed due to suberin/lignin deposition restricting apoplastic pathway.
  • Pericycle is found next to endodermis (layered - Eg: Sunflower)(2/more layered - Eg: Mulberry)
  • Pericycle → part of vascular combium
    Pericycle → cork cambium
    Pericycle → lateral roots.
  • Vascular strand contains 2-6 alternately arranged bundles of xylem and Phloem.
  • Vascular bundles for radial arrangement.
  • Xylem bundles → Tetrarch (gram, sunflower)
    Xylem bundles → Triarch (Pea)
    Xylem bundles → diarch (Tomato)
  • In between 2 adjacent Xylem bundles and Phloem there exist a conjunctive parenchyma tissue called vascular combium.
  • Pith is generally absent and if it is present there is no intercellular space.
  • Anatomy of mono cot root:
  • In a mono cot root there is no distinction between young and old root as they show no secondary growth.
  • Epiblema and cortex layer resembles dicot root
  • Casparian strip soon gets indistinguishable because of additional thickening of Endodermis.
  • The cells opposite to protoxylem ends remain primary called Transfusion cells or passage cells.
  • Pericycle is uniseriate in maize and multiseriate in similar and it does not give rise to cambium.
  • Several radial, Xylem and Phloem bundles arrange in alternate way where it is 20-30 bundles in maize and 100 or more in palm and so the condition is called polyarch.
  • Pith stores food with no Intercellular spaces.
  • Anatomy of dicot stem: Various tissues of dicot stem arrange themselves is concentric rings where in outline if it is circular for sunflower and angular for cucurbita.
  • Epidermis: In sunflower, unbranched multi cellular hair (or) trichomes are present and contain stomata.
  • Cortex is of 3 main types:
    (i) Hypodermis [Made of collenchyma tissue with inter cellular spaces]
    (ii) General cortex [With intercellular spaces containing chloroplast and also passes running oil ducts called glandular cells]
    (iii) Endodermis is a waxy layer containing barrel shaped cells with no inter cellular space and casparian strips, but contain starch [starch sheath]
  • Pericycle is heterogeneous containing both parenchyma and sclerenchyma (bundle cap) exception [Cucurbita - homogeneous]. Sclerenchymatous pericycle is also called hard bast.
  • Arrangement of Xylem and Phloem is conjoint / collateral and open
  • Arrangement of Xylem and endarch
  • A narrow strip of primary meristematic cells called cambium is between Xylem and phloem which is also called Fascicular cambium, whose functions to give rise to secondary Xylem and phloem.
  • Medullary rays or pith rays are the strips of parenchyma present between adjacent vascular bundles that connects pith to pericycle / cortex which allows radial conduction of food and water.
  • Pith forms the centre of the stem. [cucurbita → central cavity]
  • Anatomy of Monocot Root:
  • Various tissues are not arranged in concentric fashion, where the stem is solid [maize] or fistular [grass]
  • Epidermis - Outer walls have the deposition of silica and cutin and the dumb bell shaped stoma is also present for gaseous exchange.
  • Hypodermis is made of sclerenchymatous fibers that acts as heat screen.
  • Ground tissue is not distinguished into cortex, endodermis etc., where as the whole is made of parenchyma.
  • Large number of vascular bundles are scattered in the ground tissue and it is termed as Atactostele.
  • Vascular bundles → conjoint / closed.
  • Bundle sheath cells surrounding Xylem and Phloem is absent in asparagus.
  • Anatomy of leaf:
    ⇒ Leaf is of 3 different types → (i) Dorsiventral, (ii) Isobilateral, (iii) Unifacial
  • Dorsiventral mesophytic leaf:
  • The upper epidermis / adamial epidermis has no chlorophyll but cuticle and hairs may be present.
  • The lower epidermis / abquial type bear large number of pores called Hypostomata
  • Mesophyll is arranged into palisade and spongy parenchyma.
  • Palisade : Compactness ∝ light intensity
                   Marrow inter cellular space.(ICS)
                   Chloroplast is the main seat of photosynthesis
  • Spongy: Many shapes where chloroplast is less and the cells are loosely arranged with large I.C.S.
  • The vascular bundles are conjoint and collateral where X and P lies on the same radius.
  • Xylem contain all its 4 components but fibers are rare for phloem.
  • In the midrib, mesophyll is absent.
  • Isobilateral leaf:
  • Epidermis is single layered in both sides of leaf, where it is compactly arranged with cuticle.
  • At some places, bulliform / motor cells for the rolling / unrolling leaves are present.
  • Stomatal presence: Amphistomatic condition
  • The leaf contains no palisade and the whole layer resembles spongy.
  • Mesophyll is chlorine chymatous.
  • Large number of closely placed small and large vascular bundles are parallel to one another with bundle sheath cells being chlorenchymatous.
  • Xylem exhibits endarch condition.
  • Other leaf types:
  • Multilayered epidermis [Eg: Ficus, Begonia, Nerium]
  • Xerophytic leaves [spongy parenchyma is reduced] / sunken stomata.
  • Spongy sandwiched between palisade : Nerium
  • Epistomatic activity in Nymphal.

View this video for the topic from 0:59 to 51:09

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