The action of an organism or a cell toward or far from a source of light.
The motion of an organism either toward or far from a source of light
The impact of light in the motions of reduced organisms, as numerous infusorians, the zoöspores of specific algæ, etc.; in addition, the tendency to follow definite directions of movement or assume definite jobs under these types of influence. If migration is toward the foundation of light, it is called good phototaxis; if away from the light, bad phototaxis.
In botany, the taking by particular organisms or organs of a certain position with regards to the path associated with the incident rays of light, as when the zoöspores of numerous plants (Hæmatococcus, Ulothrix, etc.) place their particular long axes parallel toward path for the event rays.
In biology, active migration of organisms, or of cells, into the line of rays of light influencing all of them — positive phototaxis if toward the source of light, and unfavorable phototaxis if away from it. Compare photopathy.