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Ch 7: Leaves - Coggle Diagram

- - - - Having this located near the surface permits maximum absorption of light and ohitisynthesis.
- - - - This flat portion of the leaf is the Leaf Blade or the Lamina.
        
        The blades lower side is called the Dorsal Side or Abaxial Side and larger veins protrude from this side like backbones.
        
        The upper side of the leaf is called the Ventral Surface or Adaxial and is usually smooth.
        
        A leaf blade may be either simple or compound. A Simple Leaf has a blade of just one part.
        
        Within a leaf are Veins or bundles of vascular tissue. These distribute the water from the stem into the leaves and simultaneously collect sugars produced by photosynthesis and carry them to the stem to use or store elsewhere.
        
        In basal angiosperms and edicts, they occur in a netted pattern called Reticulate Venation.
        
        In monocots with long, Strap-shaped leaves, the larger veins run side by side with few obvious interconnections. This is Parallel Venation.
        
        Where a Compound Leaf has a blade divided into several individual parts.
        
        A compound blade has many small blades called Leaflets. Each of these are attached to a Petiolule to the extension go the petiole, the Rachis
        
        Leaves may be Palmately Compound with all the leaflets attached to the same point.
        
        They can also be Pinnately Compound with leaflets individually attached to the Rachis.
      - Leaflets are always arranged in two rows, never spiraled, whorled, or decussate phyllotaxy.
    - - If the leaf is small and narrow there may be no Petiole. The leaf is then called a Sessile Leaf instead of a Petiolate
        
        In many Monocots they typically lack a Petiole and instead the leaf base wraps around the stem to form a Sheathing Leaf Base
      - Usually in the Petiole is an Abscission Zone perpendicular to the petiole. These cells are used in cutting off the leaf when its life is over.
        
        These cells release enzymes that weaken the cells walls. As the leaf twists in the wind it breaks off and the adjacent cells around the area swell and become corky, forming a Leaf Scar.
        
        In many monocots, ferns, and cycads, this zine is not formed. Instead a protective corky layer protects the living stem tissue but the dead leaf stays on the plant until it eventually decomposes.
- - - - Larger Veins often have a mass of fibers above, below or both called the Bundle Sheath Extension
- - - - On the lower surface these prevent rapid air movement and slow water loss from the stomata.
      - In any position these make walking on and eating the leaves difficult for insects. Many grandular trichomes secrete powerful stinging compounds that prevent even large animals from eating the leaves.
        
        Poisonous granular trichomes in stinging nettle and other species prevent mammals from eating leaf tissue but also protect leaf-borne insects small enough to walk, feed, and reproduce between these trichomes.
      - These provide shade on the upper surface of the leaf. Deflecting excessive sunlight. Common in desert plants.