Phototropism in Amaryllis Flower Stalks

August 30, 2017



Photographer: Menashe Davidson
Summary Author: Menashe Davidson

As shown above, amaryllis flowers in bloom have a majestic presence. In early spring, after a required winter rest period, their bulbs typically produce one to three stalks (scapes), each with four trumpet- shaped flowers. I grow them in containers outdoors and at the beginning of each spring; beautiful flowers decorate the entrance to my home in Rishon Lezyon, Israel. Since I make sure these plants are well cared for, they produce beautiful blooms year after year -- the stalks reach a height of 25-30 in (65- 75 cm). In general, the larger the bulb, the bigger the flowers.

This year I moved one container of amaryllis just 6 ft (1.8 m) from its original site, placing it beside the entrance door but without direct sunlight (at right in top photo). Though these plants were healthy in every way, I noticed that their stalks bent in a direction where the sunlight was strongest (at right in bottom photo) in contrast to the erect stalks in other containers growing in their original space (at left in bottom photo). A tropism phenomenon is a response of a plant to a directional stimulus. In this case, the phenomenon is referred to as phototropism because the stalks are bending toward a light source. Experiments have proved that phototropism involves a mobile signal that allows more auxin to be transported down the shady side of the stalk, causing this side to grow more, bending the flower in the direction of the light source. Photos taken on April 19 and 22, 2017.