The A. defines the type of shortening of the stem and distinguishes aWistariatype and aPeriplocatype; the latter is caused only by the twisting of the stems among them. The shortening inWistariain the lowest parts of the stem is lastening even ten years after the beginning of the experience. The forces that constrast the shortening cause a condition of tension in the plant, which shortens again in a short time as soon as the obstacle is removed. The stem ofWistariaaccomplishes strong movements of twisting during its development. The rate of shortening is progressively incrcasing in the first years of life of the plant.