TROPISTIC REACTIONS OF CERIANTHUS MEMBRANACEUS

1. Cerianthus shows stereotropism and if fed regularly will remain indefinitely in glass tubes. The animal retains turgor only so long as the entire surface of the body is in contact with the glass. 2. Cerianthus is positively geotropic as regards the foot and body. It will work upward into a glass tube suspended at an angle of 35° as a result of stereotropism, but if the tube is raised to an angle of 45° the foot turns back and the animal reverses its position in the tube so that foot is down, head, up. Thus at an angle of 45° stereotropism and geotropism very nearly balance each other. 3. Light increases the muscle tone of Cerianthus; this results in positive phototropism. I x t = K. where I is the intensity of the light, t is exposure time, and K, a constant, = 0.46. Where reaction time is considered, I (t + k) = K, in which I is intensity of light, t is reaction time, k = 0.25, and K = 28.29. The two equations prove the operation of the Bunsen-Roscoe law.