Science
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Bacteria-free hydra, cultured in sterile media, were fed bacteria-free larvae of Artemia salina. Normal growth and budding were obtained in symbiotic and aposymbiotic Hydra viridis. ⋯ An exogenous budding factor, which can be provided by nonsterile Artemia larvae, or even by some bacteria, appears to be required by these nonsymbiotic hydra. This factor is endogenous in Hydra viridis.