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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