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Leaves (Evolutionary Aspects of Foliage Leaves (Main Function:…

- - - - Netted Pattern
        
        Appears in angiosperms and eudicots
    - - Run side by side down the length of the leaf
        
        Appears in Monocots
  - - - Makes the leaves leave
      - It's turning over a new leaf
  - - - Loss of water through epidermis
    - - Must be reasonably waterproof
        
        Prevention of This
      - Must allow entry of carbon dioxide
        
        Due to This
    - - Epidermal Cells
        
        Flat and Tabular
        
        Lining of the cell
      - Guard Cells
        
        Surrounds Stomata
      - Trichomes
        
        Hair-like structures on surface of leaf
        
        Deflect Excessive Sunlight
        
        Common in desert plants due to this
        
        Makes walking or chewing on the leaf difficult for insects
        
        Glandular Trichomes have qualities that can prevent even large animals from eating the leaf
    - - Due to different microclimates
      - Ex. Fewer stomata on upper side of leaf, which prevents fungi from infecting the plant
        
        Speaking of stomata, they tend to be more abundant in 'crypts'
        
        Crypts: Sunken parts of epidermis
        
        Stomata are found here due to the fact that water can go from one stoma to another
  - - - Palisade Mesophyll
        
        Main photosynthetic tissue of most plants
        
        Large Surface Area
        
        Usually one layer, but can be up to four layers thick in areas with intense sunlight
        
        Upper portion of leaf cell
        
        Some plants have Palisade Mesophyll on both portions of leaf cell
      - Spongy Mesophyll
        
        Lower portion of leaf cell
        
        Allows carbon dioxide to diffuse quickly from stomata into the rest of the leaf
  - - - Branches out into lateral veins
        
        Branches out into minor veins
        
        Important for releasing water from xylem and loading sugar into phloem
        
        Some species will have minor veins that have only xylem and others that have only phloem
        
        Only has conducting cells
        
        Needs a large surface area with palisade and spongy mesophyll, which nonconducting cells would hamper
        
        Practically the same as the midvein
      - Involved in Conduction
      - Contains primary xylem on upper side and primary phloem on lower side
    - - Composed of many fibers
      - Wrapped around Vascular Tissue
      - More difficult for insects to chew
    - - Mass of Fibers
      - Common on larger veins
      - Makes blade more rigid
      - Aids movement of water
      - Cooler than the bundle sheath
    - - Vascular bundles
      - Begin as separate vascular bundles in the body of the leaf
        
        Merges into one trace as they travel towards the petiole
      - Different bundle patterns do not have an obvious evolutionary advantage over one another
  - - - Possibly due to this, it has a few weird things going on with it
        
        The arrangement of tissue is different at the two ends of the cell
        
        Similar epidermis to lamina, but fewer stomata and trichomes
        
        Mesophyll resembles cortex in that it's compact and not too aerenchymatous
        
        Aerenchymatous just means the presence of aerenchyma
        
        Contains noticeably more collenchyma when supporting a heavy lamina
    - - Stipule Functions
        
        Protect shoot apical meristem while the leaf is undeveloped
        
        Can contribute in photosynthesis
      - Dies Young
- - - - Venus Fly Trap
        
        A.K.A. Dionaea muscipula
- - - - Smooth Margins
    - - Large Serrations
    - - Basically arrow-headed shapes that run down the length of the leaf
    - - Numerous segments jutting outward from a central piece
    - - Small, more numerous serrations
- - - - A thick leaf wouldn't put all it's chloroplasts to use, since light penetrates only a short distance due to the efficiency of those same chloroplasts
    - - Simple
        
        One Part
        
        Larger simple leaves are buoyant
        
        More common in small to medium sized plants
        
        May be due to higher percentage of photosynthetic cells
      - Compound
        
        Two or more parts
        
        One type of adaptation to prevent tearing in the leaf
        
        Individual parts are called leaflets
        
        Leaflets are connected by petiolule to the rachis, an extension of petiole
        
        Always arranged in two rows
        
        Helps Prevent Infestation
        
        More common in large plants
  - - - Shading would defeat the purpose of main function
    - - Possible for small or long leaves
        
        Ex. Aeonium
        
        Desert Plant
        
        Self-shading leaves still make use of chloroplasts due to intense sunlight
      - Monocots tend to have sessile leaves
        
        Ex. Grasses, Irises, Lilies
        
        In these leaves, the leaf base wraps around stem to form sheathing leaf base
- - - - Cells within protoderm grow outward to become leaf primordium
        
        Leaf primordium quickly outgrows shoot apical meristem
        
        As the leaf primordium continues to grow, it establishes the midvein and lamina
        
        After this final stage is complete, the product is essentially a small but fully functional leaf
        
        It will continue to grow to maturity
        
        In a compound leaf, the establishment of the lamina means growing the first two rows
        
        Cells that will become stomata, trichomes, and vascular bundles begin differentiation
        
        Consists of leaf protoderm and leaf ground meristem
        
        All cells in leaf primordium are meristematic
        
        Meristematic: Rapid division of cells to create new tissue
        
        Some cells in the center differentiates into what will become the xylem and phloem, which connects with the stem to create the veins
  - - - Gives leaf primordium a hook-like shape in early development
      - In later development, the leaf primordium wraps itself around shoot apical meristem to become a sheathing leaf base
        
        The conical leaf primordium begins development into the lamina
        
        The shoot apical meristem then forms new stem tissue and begins production of the next leaf primoridium to repeat the process
        
        The outer surface of this tube is called the abaxial epidermis
        
        The inner surface of this tube is called the adaxial epidermis