These types of movements are also called as tactic movements. The movements occur in response to some unidirectional external stimuli. Depending on the nature of the stimuli like light, temperature, chemicals etc. movements occur here.
(i) Chemotactic movement or chemotaxis – Antherozoids of Bryophytes and pteridophytes move towards the archegonia under the influence of sugars, mucilages and malic acid etc. produced by the disintegration of neck canal cells and ventral canal cells. Such movements are called chemotactic movement.
(ii) Phototactic movement or phototaxism – Some unicellular flagellated algal cells move either towards the source of diffused light (positive phototaxis) or away from the source of bright light (negative phototaxis).
(iii) Thermotactic movement or thermotaxism – many algal species such as Chlamydomonas move from cold water to warm water and from very hot water to water of medium temperature.
(iv) Thigmotaxis movement – It is the movement due to contact with the foreign body, e.g. coiling of a tendril around the support.