Crocus flowers are among the first flowers of Spring, often emerging long before the danger of snow and freezing weather has passed. Once a bud is mature, the flower will open on warm sunny days. The growth of epidermal cells of the inner and outer tepal (or petals) surfaces of flowers like the crocus and tulip are differentilly responsive to temperature. When warm, cells on the inside surface grow faster than cells on the outside surface, which causes the tepals to spread outward and thus opens the flower. When cold, like at night, cells on the inner surface slow their growth and cells on the outer surface grow relatively faster causing the flower to close. The flowers in this movie were filmed outdoors on a sunny spring morning. As the air temperature warmed, the flowers began opening. The elapsed time in depicted in this movie was about 70 min from the time the camera was activated (frames were captured at ten second intervals).