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Ch23: Seed Plants I: Seed Plants Without Flowers (Gymnosperms), Concepts,…

- - - - trees are monopodial, one main trunk w/many branches (wood composed of tracheids) annual rings, summer wood, spring wood all visible (large tracheids in spring, narrow in summer)
      - rays are thin/tall, have both ray parenchyma and ray tracheids
      - resin canals run vertically among the tracheids, horizontally among the rays
      - tough bark
  - - - pollen cones are simple cones, single short unbranched axis (microsporophylls)
      - microspore mother cells undergo meiosis and form microspores, then each of these develop into small gametophytes w/4 cells
        
        these gametophytes are shed as pollen and carried by wind
        
        conifer pollen arrives before eggs are mature, massive pollen tube digests a pathway
        
        zygote does not immediately form in conifers, some cells need to elongate first (suspensor) and push the other cells deep into the megagametophyte. These other cells (proembryo cells) develop into the embryo
      - seed cones (compact cones) consist of shoot and axillary buds, short axis bears cone bracts (instead of sporophylls) and each bract has an axillary bud that bears the megasporophylls
        
        axillary bud megasporophylls are fused laterally creating an ovuliferous scale
        
        inside the sporangium, 1 large megaspore mother cell undergoes meiosis, 3 resulting cells degenerate, 1 remains as the megaspore