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Roots (Other Types of Roots and Root Modifications (Mycorrhizae…

- - - - During Autumn, some plants will die save for the taproot, where the carbohydrates are stored
        
        When Spring comes, these plants produce a new shoot from the carbohydrates stored
        
        Somewhat similar to hibernation in animals
      - Plants that don't die out during autumn may still use storage roots for the less productive period during winter
  - - - The length of a prop root can be meters long, and growth can take many months
    - - One example of this is the mangrove
      - These roots absorb minerals through the air to be transported to the subterranean roots, due to the unfavorable soil conditions
  - - - The root epidermis, called a velamen in orchids, is composed of many layers of dead cells that act as a waterproof barrier between the orchid's roots and it's surroundings
  - - - Follows the same path of prop roots, but pulls the stem down until the base of the shoot is at soil level or below
    - - This is helpful in cases where seeds germinate at soil level or for subterranean stems
  - - - Fungal hyphae penetrate the outermost part of the cortex but never actually invades the cells
    - - Hyphae pass all the way into the root cells to right before the endodermis
        
        Includes the invasion of cells but doesn't result in the destruction of the host plasma membrane or vacuole membrane
  - - - Plants therefore rely on different methods to acquire necessary nitrogen
        
        Some prokaryotes that use nitrogen by incorporating them as amino acids and nucleotides can be used by plants to obtain nitrogen when they die
        
        The process the prokaryotes use to convert atmospheric nitrogen into a usable form is called nitrogen fixation
        
        Nitrogen-producing bacteria of genus Rhizobium enter the roots of a small number of plants by way of an infection thread
        
        When inside, the bacteria multiplies rapidly
        
        This fills the plant cells with bacteria capable of converting nitrogen into usable compounds
        
        The plant cells provide the sugars required for the process, and both parties benefit
        
        Must be noted that this process isn't necessarily voluntary. Both parties are just acting in the manner that led to their forerunner's survival
        
        During this stage, the bacterial enzymes can be damaged by oxygen.
        
        The plant produces a chemical called leghemoglobin that binds to oxygen and keeps the enzymes safe
        
        Entry of the bacteria is through the root hairs
  - - - The parasitic cells then make contact with the host xylem, and no other cells
        
        The result of this is a vessel consisting of both host and parasite cells
        
        The parasite then conducts it's own photosynthesis
  - - - Fruit of fully grown strangler fig is eaten by a bird, then it deposits the seed on another tree
        
        The seed germinates. It's roots spread down the length of the host tree, sustaining itself from rainwater for months or years
        
        Upon reaching soil, the roots grow quickly underground while those still above ground grow woody. The strangler fig soon encases the host tree
        
        Eventually the host tree dies from being shaded or due to stunted growth, and the strangler fig becomes a self-supporting tree
- - - - Selectively advantageous because the leaves that grow from the shoot should not transpire more than the roots absorb, which would be a waste of energy
- - - - Present in the seed
  - - - Common in monocots and eudicots
      - Radicle dies during or after germination in this case
      - Fibrous root systems are made up of adventitious roots
        
        Adventitious roots do not come from pre-existing roots nor are they radicles
        
        Adventitious roots increase the absorptive and transport capabilities of the root system
  - - - Result is localized growth, which means only one area grows at a time
      - The root apical meristems are protected by a thick layer of cells
        
        This is because soil has dangerous particles on a microscopic level for something as sensitive as an apical meristem
        
        This thick layer is called the root cap
        
        The root cap is constantly worn away and must be reinforced by more cells
        
        The golgi apparatus of root cap cells produces a polysaccharide called mucigel that makes it easier for the root to dig into the soil
        
        Teamwork makes the dream work
        
        Behind the root cap is the zone of elongation
        
        Expansion occurs here
        
        Very short, at three millimeters long
        
        Behind the zone of elongation is the root hair zone
        
        This is where many epidermal cells sprout outward as trichomes
        
        In case we forgot what trichomes are, they are the most interesting part of the plant in my most unbiased opinion
        
        3 more items...
        
        Only form in parts of the root that isn't elongating
- - - - As these cells get closer to the edge of the root cap, their endoplasmic reticulum shrinks, their starch grains are digested, and their golgi body produces large amounts of mucigel
    - - These cells develop dense starch grains and their endoplasmic reticulum shifts towards the front of the cell
        
        This process allows the cells to detect gravity
  - - - This is due to no irregularities, unlike the shoot
    - - This area is called the quiescent center
      - It is believed this area is a reserve of healthy cells due to their relatively strong resistance to harmful agents
        
        When a part of the root is seriously damaged, the quiescent center becomes active and reestablishes a new apical meristem
        
        The center of those cells then becomes the new quiescent center
  - - - Lifespan for individual root hairs is only a few days
      - Water pressure, called root pressure, builds up due to root hair's absorptive efficiency
        
        The strong endodermis prevents the root pressure from resulting in a leakage of water
    - - The walls of the endodermis has different qualities depending on the area it is found
        
        The walls closest to to the cortex and vascular tissue are not too different from average primary walls
        
        The walls on the borders of other endodermis cells are waterproof
        
        Along the entirety of the endodermis, these walls form a layer within the endodermis cells called the Casparian strips
        
        This is the specific part of the endodermis that controls what minerals enter the xylem water stream
        
        Without the endodermis, any mineral inside the intercellular space could move into the xylem
        
        The Casparian strips are also impermeable
        
        Due to this, only minerals that are absorbed by endodermal protoplasts make it into the vascular tissue
        
        The vascular tissue is only in any real danger of unwanted minerals when the endodermis is immature
        
        Some endodermis cells consist of only Casparian Strips
        
        These cells are called passage cells due to a past misunderstanding
        
        Currently thought to be underdeveloped cells
    - - Cortex
        
        A mass of mostly parenchyma cells between the epidermis and endodermis
        
        Constitutes most of the space in the root hair zone
      - Epidermis
        
        The outer layer of dermal cells
      - Endodermis
        
        The inner layer of dermal cells
      - Vascular Tissue
        
        Cells enclosed within the endodermis
    - - In some monocots, strands of xylem and phloem are distributed in ground tissue within the endodermis
      - Xylem forms a mass in the center. Surrounding the mass of xylem are strands of phloem
        
        This is the arrangement of the vascular tissue in most plants except some monocots
      - Besides differences in arrangement, vascular tissue of the root hair zone is akin to those found in the stem and leaf
      - The cells enclosed in the endodermis that aren't xylem or phloem are collectively called the pericycle
        
        The pericycle is made up of parenchyma cells
        
        Lateral roots sprout from the pericycle
- - - - As this happens, the endodermis will either be torn or create a thin layer over the primordium
        
        Ultimately, this will result in the destruction of the endodermis
      - By the time the root primordium makes it's way out of the parent root, it would already have it's own root cap
        
        The rest of the process continues as it did for the parent root