What are 2 mutualistic relationships that involve plants?

Question

I would like to know two mutualistic relationships (both benifit) that involve plants.
If you could mention a few examples, that'd be great.

Answer 1

Plants of the pea family, leguminous plants, have hundreds of little round structures called nodules on their roots. The roots secrete a chemical substance which stimulates certain bacteria to grow and divide. These bacteria which live inside the root nodules can take nitrogen from the air and make nitrates. These nitrates are needed by the plant for growth. In return the bacteria are protected in the root nodules and gain certain nutrients from the plant which are necessary for their own growth.

Even some plants have a darker, parasitic side. Common cow-wheat (Melampyrum pratense) is semi-parasitic on the roots of a number of plants including blaeberry (Vaccinium myrtillus), while lousewort (Pedicularis sylvatica) and yellow rattle (Rhinanthus minor) are found on grasses. Parasitic plants can increase the diversity of plant species in an area by keeping more dominant species in check.

Answer 2

Lichen has an interesting mutualistic relationship, its a fungi that provides the living space for photosynthetic algae, which in turn makes the food. The combined organism can live in hot and dry places that neither an algae or a fungus can normally live. Such organisms are some of the the most cold and heat tolerant on earth. The can be found in deserts and in the arctic circle.

Answer 3

One of the most interesting cases of mutualism I know of is that of coral. Corals are tiny animals that produce hard calcareous shells around themselves, and usually build them on the shells of corals that have already died - thus, coral reefs. They have a form of algae inside them, called zooxanthellae. The algae photosynthesize (use CO2 and H2O and energy from the sun to make sugar and O2), and provide some of the sugar to the coral as food. The CO2 they use comes from the respiration of the coral's cells ("burning" sugar in the presence of O2 to make energy), and the coral can also use the O2 the algae produce. The algae take some other waste products from the coral and break it down into nitrogen and phosphorus, which are nutrients for the algae. There's an interesting web site at
http://www.onr.navy.mil/focus/ocean/habitats/coral1.htm