Despite many studies of foraminifers, very few suggestions have been made concerning the function of the test. If the adaptive significance of the test were known, this would provide a theoretical basis for understanding the ecological importance of test shape and construction.

Observation of the behavior of many shallow-water species in response to environmental changes indicates that the test may function as a chemical and physical buffer between the organism and the environment. Shallow-water foraminifers construct a test of much larger volume than needed merely to house the living protoplasm. Under conditions of stress, Sorites, Planorbulina, Bolivina, Discorbis, and miliolids occupy only the inner chambers of the test; the outer chambers may be filled with a less dense, highly vesiculate cytoplasm, or may be empty. If the individual chambers of the test are connected only through one or a few small openings, adverse osmotic effects produced by changes in salinity can affect the protoplasm only slowly. Complex tests may thus serve as a baffle to reduce t e rate of chemical diffusion.

Some chambers are sites of concentration of symbiotic algae. In Elphidium, algal-filled chambers are in communication with each other, but the apertures of the final chamber are sealed. The foraminifer communicates with the outside only through the tortuous passageways of the canal system except during relatively brief intervals of chamber addition. The test functions as a protected greenhouse for the foraminifers' symbiotic algae.

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