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Ch 6: Tissues and the Primary Growth of Stems, No obvious selective…

- - - - The body of a herb has three parts, leaves, stems, and roots
      - Often lives less than a year (Snapdragons, Beans, Corn) Although some live longer than a year and grow for far longer. (Lilies and Irises)
        
        Plam Trees are large, perennial, and hard but don't actually have wood which makes them giant herbs
      - Its Primary tissues are its tissues.
      - The outermost surface of a Herbaceous stem is the Epidermis a single layer of Parenchyma cells. Differs from the human epidermis since the human epidermis is a lot thicker.
        
        Shields the plant from bacteria, fungi, and inects. While also preventing the loss of water.
        
        Other tangential walls are encrusted with Cutin which is a fatty substance that makes the wall impermeable to water.
        
        Cutin build up is a more or less pure layer called the Cuticle
        
        Under more severe conditions, a cuticle isn't even sufficient enough and a layer of wax may be present outside the cuticle.
        
        Cutin and wax resist digestive enzymes and provide defense against pathogens like bacteria and fungi.
        
        Unfortunately these also inhibit Co2 needed for photosynthesis making a totally impermeable epidermis would cause the plant to starve.
        
        However the epidermis contains pairs of Guard Cells with a hole Stomatal Pore between them
        
        2 more items...
        
        Interior to the Epidermis is the Cortex.
        
        Protoderm refers to Epidermal cells that are in the early stages of differentiation.
    - - Primary tissues are its tissues
      - Only consists of a primary plant body
      - All Herbaceous parts of plant body
      - Shoot and Root Apical Meristems
      - Composed of Primary Tissues; Epidermis, Cortex, Pith
    - - Woody plants (Trees and shrubs like Oaks, Maples, Roses, and Magnolias) Wood and Bark are Secondary Tissues
      - Derived from Meristems other than Apical Meristems
      - Composed of Secondary tissues; Wood and Bark
      - All woody and bark-covered parts of a plant
- - - - Mechanical Sclerenchyma subdivided into long fibers and short Sclereids both of these have elastic secondary walls.
        
        Sclereids short and more or less isodiametric. Acts brittle and inflexible. Masses of these form hard surfaces that are inpenetrable.
      - Conducting Sclerenchyma transport water and is one type of vascular cell.
  - - - Parenchyma Tissues that conducts nutrients over long distances a Phloem
    - - Chlorenchyma Cells are Parenchyma Cells involved in Photosynthesis. These have numerous chloroplasts and thin walls that allow light and CO2 to pass through to the chloroplasts.
        
        Grandular Cells are also Parenchyma Cells. These cells secret Nectar, fragrances, resins and oils. Typically contain few chloroplasts but have a raised amount of Dictyosomes and endoplasmic reticulum.
        
        Transfer cells are Parenchyma Cells that mediate short distance transport of material by means of large, extensive plasma membrane capable of holding many molecular pumps.
        
        These transfer large amounts of sugar and minerals into themselves, transforms them metabolically and then transports them back out.
- - - - The bud is covered by Bud Scales which are small, corky and waxy. These protect the delicate organs inside.
        
        At the very tip of each stem is a Terminal Bud
        
        Phyllotaxy is the arrangement leaves on a stem. This is important to the positioning of the leaves so they do not accidentally shade each other.
        
        The capacity for a plant to 'move around' or 'explore' is even more advanced in Stolons also called runners. The internodes on these are long and thin and leaves don't expand. Making these extend greatly without using much energy reserves.
        
        Rhizomes are fleshy horizontal stems that allow a plant to spread underground. (Bamboo, Irises, and Canna Lilies)
        
        Tubers are horizontal like Rhizomes, but only grow for a short period and are mainly a means of storing nutrients. (Potatoes) The word tuber is used for any bulky underground plant organ.
        
        Corms are vertical, thick stems with thin papery leaves.
        
        Nutrient storage is especially important to certain shoots like the Bulbs. These are short shoots with thick, fleshy leaves. (Onions, Garlic, Daffodils)
        
        Alternate-One leaf per node
        Opposite- Two leaves per node
        Decussate- Leaves located in four rows
        Whorled-Three or more leaves per node
        Spiral- Leaves aren't aligned with their near neighbor.
        Distichous-Leaves only located in two rows
      - Every Axil has a bud but very few make a branch. Most remain dormant or produce flowers.
      - May be advantageous for Axillary Buds to remain dormant so that all resources are concentrated in the growth of a vertical main shoot, the Trunk, which allows the plant to reach brighter light in the top of the forest canopy.
- - - - Individual cells that produce both primary and secondary walls before dying at maturity.
        
        However an entire region of primary and secondary walls is missing.
        
        During the final stages of differentiation, a large hole called a Perforation is digested through a particular site of the primary wall, often removing the entire end wall.
      - Entire stack of vessel elements is a Vessel.
    - - In the simplest tracheary element, only a small amount of secondary wall is present, organized into a set of rings, called Annular Thickenings
        
        With Helical Thickening the secondary wall exists as one to three helices interior to the primary wall.
        
        Scalariform Thickening provides more strength because the secondary wall underlies most of the inner sirface of the primary wall and is fairly extensive. The area where the wall is absent is called a pit.
        
        Reticulate Thickening the secondary wall is deposited win the shape of a net
        
        Strongest of thes is the Circular Bordered Pits. Virtually all primary wall is underlain with secondary wall. The pits that allow water movement are weak points in the wall, but the weakness is reduced by a Border of extra wall material around the pit.
      - Metaxylem is the largest Tracheary element because they had the longest time for growth before differentiation.
  - - - These end wall sieve areas with large sieve pores are Sieve Plates.
      - Controlled by Companion Cells these cells are often smaller than the accompanying conducting cell and have a prominent nucleus and dense cytoplasm filled with ribosomes. Loads sugars into and out of the sieve tube members.
    - - Associated with Albuminous Cells
  - - - The region just below the Apical Meristem is the Subapical Meristem
        
        The first Xylem to appear are called the ProtoXylem. Cells around them continue to grow and expand, but soon those just exterior to them also begin to differ, because these have expanded for longer time they develop into treachery elements that are even larger than the first.
        
        Because these cells have had the longest time for growth before differentiation they develop into the largest treachery elements of them all: Metaxylem
      - Similar process occurs in the outer part of each vascular bundle. The exterior cells mature as Protophloem and cells closest to the Metaxylem become Metaphloem