Whether in the water, soil, or other terrestrial habitats, the fungi carry on their existence in the presence of other living organisms. Only when we take the fungi into the laboratory and establish pure cultures are the fungi truly separated during their growth from other organisms. This living together, which is the normal situation in nature for all living things, is referred to as symbiosis. Symbiosis is commonly studied by taking a particular organism, or group of organisms, and examining any special relationships that species of a different taxon may have with it. For example, the relationship of insects with pollination of flowering plants or the role of bacteria of the genus Rhizobium in nitrogen fixation by leguminous plants are types of symbiotic relationships that have intrigued scientists. These happen to be examples in which both members of the association benefit, but that is not necessarily the case in symbiotic relationships. The word symbiosis simply means living together, and does not imply any advantage or disadvantage to either member of the partnership.