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SeedPlants213-page16 - | Many Archegonia form in Ovule |...

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Seed-Dispersing Plants - 16 Sample Life History of a Pine Year One:Sporogenous tissue is initiated and enclosed within bud scales. Year Two: Spring A. Male: Maturation of male microsporangia (male cones) Each cone scale equals one microsporophyll. | Meiosis | Microspores forming male gametophyte or pollen grain (2 prothallial cells, 1 generative cell, 1 tube cell, and "wings") | Dispersal by wind to female B. Female Maturation of female megasporangia Each cone is a reduced branch system with 2 ovules per cone scale | Ovule (Megasporangium with nucellus, integuments and micropyle) Meiosis | Megaspore C. Pollination A period of dormancy (about 6 months) follows pollination Year Two: Late in Season Megaspore develops in Female Ovules | Free nuclear divisions of megaspore tissue
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Unformatted text preview: | Many Archegonia form in Ovule | Eggs form Year Three Early Season A. Fertilization Eggs + Sperms | Zygotes | Many embryos start developing | One embryo per ovule survives and matures | Seed B. Seed Maturation Ovule integuments form seed coat Embryo has many cotyledons Nucellus provides nutrients Cone scale (or fleshy aril in Yew) protects Year Three Late Season Seed Release Cone scales usually open to release seeds in fall Some cones stay sealed until appropriate condition for germination occurs (such as in Redwoods, which germinate best after fire) Some cone scales are deciduous, as in true firs. Some cone scales are fleshy, such as the aril of yews...
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