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Tuesday, 31 January 2017

Anatomy of flowering plants III


Dicotyledonous Stem
  • Epidermis is the outermost layer of dicot stems having thin layer of cuticle, may contain trichomes and hairs.
  • Cortex is divided into three sub layers- outer hypodermis (collenchymatous), middle cortical layer (parenchymatous) and inner endodermis, which is rich in starch grains so, also known as starch sheath.
  • Vascular bundles are conjoint, open, endarch with protoxylem. Pith is the parenchymatous with intercellular spaces.
Dicots Stem (TS)
Monocotyledonous Stem
They have sclerenchymatous hypodermis, large number of scattered vascular bundles surrounded by sclerenchymatous bundle sheath. Vascular bundles closed and conjoint. Phloem parenchyma is absent.

Dicotyledonous Leaf (Dorsi-ventral)
  • Vertical section through lemima shows three regions- epidermis, mesophyll and vascular system.
  • Epidermis covers both upper (adaxial) and lower (abaxial) surface. Abaxial surface have more stomata.
  • Mesophyll  bears  chlorophyll  to  carryout  photosynthesis,  are made  up  of parenchyma. Spongy parenchyma are spherical and loosely arranged but palisade parenchyma are elongated.
  • Vascular system includes vascular bundles, which are seen as veins and midribs. Vascular bundles are surrounded by thick bundle sheath cells.
Dicots leaf (VS)
Monocotyledonous Leaf (Isobilateral)
  • Monocots leaves are similar to dicots leaves anatomically except stomata are present on both surfaces of epidermis and mesophyll cells are not differentiated as spongy and palisade cells.
  • In grasses, some adaxial epidermal cell with veins modify into large, empty, colourless cells called bulliform cells. These cells make the leaves turgid when water absorbed and curls in case of water stress.


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