20_Maloof_angiospermsI_Outline

20_Maloof_angiospermsI_Outline - Lecture 20/ Plant Lecture...

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Lecture 20/ Plant Lecture 8: Angiopserms I 1) Additional features seen in some seed plants a) Double fertilization i) Typically pollen produces two sperm (1) Conifers: one fertilizes, one dies (not double fertilization) (2) Some gnetum: both fertilize different eggs (3) Angiosperms: one fertilizes egg (to make zygote and then embryo), one fertilizes “central cell” to make endosperm, a nutritive tissue to nourish the seedling. b) Loss of swimming sperm (relate to pollination): lost in conifers, gnetophyta, angiosperms c) Other gnetum hypotheses/characters d) Loss of archegonia: some gnetophyta, all angiosperms e) Xylem vessels: found in angiosperms and gentophyta i) Gnetum resemble the Angiosperms in many respects. This had led taxonomists to consider gnetophytes to be the closest living relatives of the angiosperms. How should these features be though of now?. (1) No Archegonia (2) Vessels and Fibers (3) Some strobili resemble inflorescences (flower clusters) (4) Double fertilization 2) The angiosperms have two additional features that are key synapmorphies: flowers and fruit a) Flowers: pollen delivery device. How does pollen get to the ovule? i) In most gymnosperms pollen is dispersed by wind. Seems inefficient. Most pollen will never make it, so vast amounts have to be produced. ii) The angiosperms mostly use animals to pollinate. The flower functions both to attract and reward animals for pollination. b)
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20_Maloof_angiospermsI_Outline - Lecture 20/ Plant Lecture...

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