AEBI 210 Lecture Notes - Phloem, Megaspore, Gymnosperm
8 Jan 2013
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Document Summary
Seed plants are heterosporic megaphylls which have microspores and megaspores. A megaspore is contained within a nucellus (fleshy megasporangium) Have pollen which brings the male gamete to the female one. Do not require water for fertilization to occur. The method of reproduction for most extant plants. A seed has an embryo and food supply within a resistant coat. A fertile nucellus envelope near integuments contains a megagametophtye. Progymnosperms had wood and secondary phloem, but reproduced by free spores. Embryo developed in the megagametophyte inside the megaspore. An integument surrounds the megasporangium, but has a micropyle (small opening) The apex of the megasporangium was modified to receive pollen. This new unit is called the ovule, which develops into the seed. The female gametophyte is always protected by the sporangium. The male gametophyte has evolved into a 3 or 4 celled pollen grain. Two sperm cells grow inside the pollen grain.
