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Flowers & Reproduction (Flower Structure & Cross-Pollination…

- - - - establish roots
    - - the ends become separated & act as individuals
- - - - either sperms or eggs, by meiosis
    - - 1 sperm & 1 egg are brought together, forming a new single diploid cell
      - grows to become a new individual that is diploid & resembles its parents
    - - trees, shrubs & herbs are part of this phase
    - - always diploid
      - have organs w/ cells capable of undergoing meiosis
    - - in this process they produce the diploid zygote
    - - small sperm cells (microgametes) that swim
      - large eggs (megagametes) that do not swim
  - - - at very end of the axis, where other flower parts are attached, is the receptacle
    - - sepals, petals, stamens & carpels
    - - some lack 1 or 2 & are incomplete flowers
    - - all the sepals together are referred to as the calyx
    - - together they make the corolla
    - - known as androecium
      - 2 parts:
        
        the filament (its stalk)
        
        anther, where pollen is produced
    - - 3 main parts:
        
        stigma
        
        style
        
        ovary
        
        Inside the ovary are placentae
    - - Megagametophyte
        
        Within the ovule the surviving megaspore develops into a megagametophyte
        
        technical term for a multinucleate megagametophyte is embryo sac
        
        The 7 cells are 1 large central cell
        
        with 2 polar nuclei, 3 small antipodal cells
        
        & an egg apparatus consisting of 2 synergids & an egg
      - Microgametophyte
        
        The microgametophyte (the pollen tube) is protected & nourished by the style tissue
        
        consisting of at most 3 cells located within the original pollen cell wall
        
        Microspores develop into microgametophytes
  - - - fusion of the protoplasts of the gametes,
        
        and karyogamy, fusion of the nuclei
    - - triploid, containing 3 full sets of genes
    - - Because both sperm nuclei undergo fusions
  - - - but always by both nuclear and cellular divisions
    - - part of which later becomes the embryo proper,
        
        the other part becomes a short stalk-like structure, the suspensor,
        
        which pushes the embryo deep into the endosperm
    - - developing into an embryo
    - - If endosperm is sparse or absent at maturity, the seed is exalbuminous
  - - - exocarp is the outer layer - the skin or peel
      - mesocarp is the middle layer - flesh
      - endocarp is the outermost layer
        
        may be tough like the stones or pit of a cherry or it may be thin
- - - - pollination of a carpel by pollen from the same flower or another flower on the same plant
  - - - is prevented if anthers and stigmas mature at different times
    - - older flowers could be self-pollinated by freshly opened flowers of the same plant
  - - - chemical reactions between pollen & carpels that prevent pollen growth
  - - - because they produce the critically important spores
  - - - brightly colored petals, fragrances, & nectar are a waste of material and energy
    - - mutations that resulted in pigments, fragrances, or sugar-rich secretions became adaptive
    - - a flower becoming adapted for visitation by a particular insect
        
        & the insect for efficient exploitation of the flower
  - - - landing on a compatible stigma is small, so huge numbers of grains must be produced
  - - - Burying the ovaries deep within the flower provides further protection
- - - - 1 small flower may be overlooked, but not a hundred close together
  - - - has only a limited potential for growth
    - - the lowest or outermost flowers open first
- - - - dehiscent
    - - indehiscent
    - - indehiscent fruits do not