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SeedPlants213-page13 - are wind pollinated and many produce...

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Seed-Dispersing Plants - 13 The male strobili, or cones, are formed by spirally arranged microsporophylls, on the strobilus axis; Each microsporophyll of the male strobilus has two microsporangia. The gametophyte stage is greatly reduced and retained within both male and female sporangia (often called pollen sac and ovule for some reason). Male gametophytes form pollen grains. The mature pollen grain consists of four cells: two prothallial cells, a generative cell and a tube cell, which grows the pollen tube through which the sperm migrates to the egg once pollen is successfully delivered to the female gametophyte. Sperm is formed from the generative cell. Conifers
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Unformatted text preview: are wind pollinated and many produce distinctive winged pollen. Male strobili Strobilus xs Microsporangium Pollen The female gametophyte, which develops from the megaspore, contains two or more archegonia. The surrounding megasporangial tissue is modified into the integument layers, which protect the gametophyte and eventually form the seed coat, and the nucellus layers from which the gametophyte obtains nutrients. In pines, the female gametophyte takes one year to develop after pollination. The pollen grain germinates at pollination and grows the pollen tube, but the generative cell does not form sperm until the female gametophyte is mature....
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