Overly frequent stimulations are no longer perceived by the plant and can even reduce its sensitivity. At another level,this sensitivity of rose to mechanical stress that is, in fact, triggered by relatively little stimulation, should serve as a warning to the experimenter of the risk of falsifying test results if the plants are handled too much when they are measured. This “observer” effect was revealed by De Boeck et al. (2008)ในต้นปอปลาร์