Definitions

from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. The movement of an organism or a cell toward or away from a source of light.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. The movement of an organism either towards or away from a source of light

from the GNU version of the Collaborative International Dictionary of English

  • n. The influence of light on the movements of low organisms, as various infusorians, the zoöspores of certain algæ, etc.; also, the tendency to follow definite directions of motion or assume definite positions under such influence. If the migration is toward the source of light, it is termed positive phototaxis; if away from the light, negative phototaxis.

from The Century Dictionary and Cyclopedia

  • n. In botany, the taking by certain organisms or organs of a definite position with reference to the direction of the incident rays of light, as when the zoöspores of various plants (Hæmatococcus, Ulothrix, etc.) place their long axes parallel to the direction of the incident rays.
  • n. In biology, active migration of organisms, or of cells, in the line of rays of light affecting them — positive phototaxis if toward the source of light, and negative phototaxis if away from it. Compare photopathy.

Etymologies

photo- +‎ taxis (Wiktionary)

Examples

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