Epidermis

• Outer layer of cells that protects the internal stem tissues

• A layer of cuticle coats the epidermis to protect against dessication and UV radiation

• Stomata are dotted along the epidermis for gas exchange

  • In monocots, like grasses, stomata occur on both sides of leaf

  • In eudicots, like trees, stomata are only on the abaxial side of leaf

Mesophyll layer

• The layer of parenchyma cells involved in photosynthesis and gas exchange

• In Eudicots, this layer is separated into two layers: palisade layer and spongy layer

Palisade layer

• A layer of chlorenchyma cells, where light interception for photosynthesis occurs

• This layer is toward the adaxial, or upper, side of the leaf

Spongy layer

• A layer of aerenchyma cells, where gas exchange for photosynthesis occurs

• This layer is toward the abaxial, or lower, side of the leaf

Vascular Bundles or Veins

• The veins of the leaves consists of vascular bundles

• The vascular bundles are composed of primary xylem and primary phloem, which formed from the shoot apical meristem and the procambium

What is the morphology of leaves?

Blade

• The flattened, photosynthetic portion of the leaf 

Petiole

• The thin, stalk-like portion; sometimes called the stalk

• The petiole connects the blade to the stem

• Not all leaves possess a petiole (=apetiolate) 

Stipules

• • The leaf-like outgrowths from petiole near stem

  • Most leaves do not have stipules (=non-stipulate) 

Veins

• • Veins are the visible vascular bundles running through the leaf