Stem bending was determined by assessing the accompanying change in the position of the floral head. As the flower is perpendicular to the stem the upper surface of the floral head was initially about 20◦ with respect to the horizontal. When the stems started bending the angle of the floral head surface moved to more than 20◦ with the horizontal (Fig. 1, left). At one
point in time the upper surface of the floral head could be in a vertical position (Fig. 1, middle). When stem bending went further, the floral head surface moved to beyond vertical (Fig. 1, right). This was defined as stem bending.