Thigmotropism in Organs of the Bean Plant (Phaseolus vulgaris L.)

When each vegetative aerial organ of the young bean plant is unilaterally mechanically perturbed by gentle rubbing, it exhibits positive thigmotropism. The internodes undergo only moderate thigmotropism, but leaves and petioles bend much more, especially when they are rubbed on their abaxial surfaces. When the abaxial surface of one petiole is rubbed, it bends down, but the opposite petiole bends upward at the stem-petiole pulvinus. These observations are interpreted in terms of the vining habit of bean plants.