The History of Land PlantsCase 3: How have plants changed?
Seed plant, boldly growing where no plant has grown before.
Why are seeds better than spores?
Although spore coats allowed plants to live on land, reproduction (the fusing of egg and sperm) still has to happen in water (see moss and fern posters). So spore-bearing plants cannot reproduce without rain or other sources of water, and must live near water.
A number of plants evolved a different method of reproduction including the seed plants. The female spore that makes the egg is surrounded by tissue and retained on the plant making an ovule (or pre-seed). Pollination occurred when the male spore with the sperm is blown on to the ovule, and grows a tube into the egg. Fertilization occurs when the sperm reaches the egg. This new structure is a seed with a protective seed coat, food and an embryo (see pine and lily posters).
The result is that seed plants are less dependent on water than non-seed spore-bearing plants. Once seed plants evolve their fossils begin to be found in areas that are farther from water and are drier. The seed allowed green plants to invade all the terrestrial habitats found on earth, except ice.
To see close-ups of the specimens in this display, click here. Monster Plants That Created Coal Flowering Plants: The New Revolution
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