When ocean water rises above 20-21° C. in the Woods Hole region the hydranths of Tubularia crocea are lost and the coenosarc retreats into the perisarc. The colonies remain in this dormant condition until the temperature drops in autumn. Growth is then resumed. The dormant colonies can be stimulated to produce hydranths in three days by keeping them at 18.4° C. It is thought that temperature is the principal agent in the disappearance and reappearance of active colonies.