The unicellular freshwater flagellate Euglena gracilis regulates its position in the water
column by means of phototactic and gravitactic behavior. Recent experiments have revealed
that the cells switch between negative and positive gravitaxis depending upon
environmental stimuli such as solar radiation. In this study, the effect of increased salinity on
gravitaxis in Euglena gracilis was investigated. In some experiments it was found that salt
concentrations up to 5 g L− 1 (in some experiments 10 g L− 1) increased the motility, velocity …