Quantitative analysis of an inhibitory gradient field in the hydrozoan stolon

An inhibitory field which emanates from the mobile tips of elongating stolons of colonial hydroids has been identified and analyzed. It extends proximally with decreasing intensity for about 400-700 μm and ensures that branching sites occur at appropriate distances along the stolon. The local strengths of inhibition within the field have been measured with a new method which permits high temporal and spatial resolution. Kinetic studies reveal three characteristics. First, inhibition decays rather rapidly after removal of its source. The half life is about 30 min. Second, loss of inhibition immediately triggers initiation of future tip formation. Third, restoration and spreading of inhibition are slow processes which take 8-24 h to recover 90% of the original inhibitory levels.