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Leaves (External Structure of foliage leaves (Petiole (stalk) pic #…

- - - - dorsal surface
      - larger vein like a backbone
        
        abaxial side
    - - Ventral surface
      - usually rather smooth
  - - - irises
      - lilies
      - Grasses
      - agaves
      - Yuccas
    - - leaf base wraps around the stem
        
        forms a sheathing leaf base
        
        can flutter without a petiole
  - - - has a blade of just one part
      - largest is the Victoria water lily pic
      - larger one are composed mainly of photosynthetic cells
    - - has a blade divided into several individual parts
      - "pretorn"
      - small many blades
        
        leaflets
        
        each attached by petiolule
      - Petiolule
        
        to an extension of the petiole, the rachis
- - - - Portulacaeae pic
      - Aizoaceae
      - families Crassulaceae pic
    - - lack of air spaces make the mesophyll transparent
      - allowing light to come through
  - - - with this extended lifetime and prolonged productivity, sclerenchymatous leaves are feasible, and their hardness makes then more resistant to
        
        fungi
        
        freezing temps
        
        animals
        
        UV rays
  - - - Agathis
      - Araucaria
      - podocarpus
    - - thuja
      - Cupressus
- - - - that extends upward as a narrow cone pic
- - - - consisting of a large percentage of flat tabular, ordinary epidermal cells guard cell and trichomes may be abundant
    - - water lost through the epidermis
  - - - along the upper surface of most leaves is a layer of cells
      - which main photosynthetic tissue of most plants
      - cells are separated slightly so that each cell has most of its surface exposed to the intracellular spaces
      - are often only one thick layer, but in regions with intense, penetrating sunlight, it may be three of four layers thick
    - - the large surface gives maximum area for dissolution
        
        tightly pack cells could not absorb enough carbon dioxide for efficient photosynthesis
    - - open, loose aerenchyma that permits carbon dioxide to diffuse rapidly away from stomata into all parts of the of the leaf interior
  - - - also called a midvein
      - from which lateral veins emerge that branch into narrow minor veins
    - - many fibers arranged as a sheath
      - makes it difficult for insects to chew into vascular tissues
    - - midrib and lateral vein are involved mostly in construction
    - - examples
        
        tannin
        
        starch storage
        
        Mucilage
  - - - example
        
        rhubarb
        
        celery
        
        palm
        
        water lilies
    - - are transitions between the stem and the lamina
    - - 1 or more bundles
        
        called leaf traces
- - - - should be flat and thin for maximum absorption
      - most tissues should be alive and differentiated into chorophyll-rich chlorenchyma for photosynthesis
    - - elevate leaves and conduct material to and from them among other activities
      - Maximum conduction and support with minimum expenditure of construction material require a cylindrical stem
      - also much of the stem all of its tracheary elements and most fibers must die to be functional
    - - Agave pic
      - Yucca pic