Physical Movements: The structures involved in this type of movement are mostly dead. Xerochasy: Structures like the wall of fruits, sporangia, capsules, have differential wall thickenings. During dry weather conditions, they loose water to atmosphere. Because of this, the thick walls contract as a result they break open along with the line of dehiscence, where the cell walls are thin and susceptible. Hydrochasy: Certain structures, made up of hydrophilic substances, are capable of imbibing water as well. Due to imbibition of water they swell. Due to imbibition of water peristomial teeth in Moss capsules, elators in equisetum, etc. show movements. In fact such movements help in the dispersal of spores.
Vital Movements: Plant movements due to the activity of living structures are called vital movements. They are further classified into different kinds. In some plants, particularly unicellular algae, the entire cell moves from place to place or from one position to the other or the protoplasm by itself shows continuous flux by physical displacement. In others, where the plant body is fixed in the soil, certain structures show bending or curvature movements. Furthermore, some of the movements are auto regulated and propelled by innate mechanisms but other movements are induced by stimuli. In this case the entire living cell is involved either in the movement of protoplasm or the entire body of the plant cell from one place to another. These movements may be autonomous and induced.
