The Open Door Web Site
Part XIX : Colonizing and Populating Habitats : Seeds and Spores Index
COLONIZING AND POPULATING HABITATS
The Bryophytes: Liverworts
These are small plants which never grow more than a few centimeters tall. Their roots, if they have any at all, are very small and simple. The bryophytes are always found growing where conditions are wet or where the climate is wet for a part of the year. This is important because as we shall see it helps them to reproduce.
The liverworts are plants which are very delicate. They can easily dry out and die. Their bodies are flat and broad and they grow in dense mats over rocks beside streams and waterfalls.
In the early spring, as the amount of daylight increases and the temperature rises, liverworts start to grow a long stem with a ball-shaped end to it. This ball will gradually turn black or brown and, eventually, it will burst open. The ball is called a spore case or sporangium (pl. sporangia). When the spore case bursts open it releases thousands of microscopic spores into the air. The liverworts produce spores to be carried in the air currents. When the spore lands on the soil, if the conditions are suitable it will germinate and grow into a new liverwort plant.
The spore case which grows out of the liverwort is the product of fertilization. One part of the liverwort's thallus produces sperm cells. On another part of the thallus egg cells are produced. The sperm cells swim across the surface of the liverwort in a film of water. This explains why liverworts need to be near water or covered in water a large part of the time. Without water they cannot reproduce. So that the sperm cells can find the egg cells they are attracted to the egg cells by a chemical.
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