Chapter 29

Chapter 29 - Chapter 29: The evolution of seed plants 29.1...

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Chapter 29: The evolution of seed plants 29.1 – How did seed plants become today’s dominant vegetation? o During the Devonian, in a hot environment, plants developed woody stems and xylem Called secondary growth o Progymnosperms first displayed secondary growth o By late Devonian plants had ferny foliage, but seeds o Seed plants include Gymnosperms (pines, cycads) Angiosperms (flowering plants) o As time goes on, seed plant sporophytes depend less on the gametophyte o Only earliest gymnosperms had had swimming sperm o Seed plants are heterosporous, but form separate microsporangia and megasporangia E.g. stamen and pistils o Microsporangia release pollen grains o Pollen have a very resilient surface made up of sporopollenin o Megaspores are not shed, they stay on the sporophyte and grow o Megasporangia are surrounded by sterile sporphytic structures forming an integument o The megasporangium and the integument is called the ovule – which becomes a seed o Pollination is the process of a pollen grain landing close to the female gametophyte of the same species o The pollen grain reaches a specific point and burrows into the megagametophyte creating a pollen tube o Once fertilized, the diploid zygote divides till it forms a multicellular seed o Seed coat develops from integument o The haploid female gametophytic tissue is the second generation o The center of the seed is the third generation
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This note was uploaded on 09/08/2011 for the course LS 1 taught by Professor Thomas during the Summer '05 term at UCLA.

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Chapter 29 - Chapter 29: The evolution of seed plants 29.1...

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