Removal of potassium from Hydra culture medium produces a decrease in intracellular potassium and a parallel decrease in asexual growth rate. Rubidium and caesium are ineffective as substitutes for potassium in the maintenance of growth rate. Increases in intracellular potassium parallel increases in growth rate up to a level somewhat below the normal steady-state level of intracellular potassium. The full potassium requirement for maximum effect on budding can be acquired from food or external medium. High levels of external potassium suppress budding but do not alter intracellular potassium levels.

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