SYMBIOSIS

designates the biological partnership frequently found between organisms of different types. Among the best known cases of mutualistic symbiosis, (7.e. an a ociation from which each party derives benefit) are the relationships between algoid, and fungoid lichens, between radiolarians and their symbiotic algae, and that between the legumes Aad the bacteria of their root tubercles. In the last case the presence of the bacteria make it po ible for the plant to utilize the free nitrogen present in the soil; in other species the plant must be supplied with nitrogen combined in a soluble salt. Antagonistic symbiosis or parasitism such as occurs with parasitic fungi, is frequently difficult to differentiate accurately.