A Hierarchy of Histo-Incompatibility Inhydractinia Echinata

Hydractinia represents a simple system in which to study induction, cellular-recognition mechanisms, and hyperplastic growth. 2. Among various strains isolated from nature, there is a tissue incompatibility upon contact which results in the production of hyperplastic stolons (overgrowth) in one or both colonies of any binary combination of strains. The induction of hyperplasia probably involves surface-bound molecules produced by the ectoderm. 3. A hierarchy of hyperplastic potential was established in two groups of ten strains each. A correlation between colonial morphology and rank in the hierarchy was noted. 4. Consistency of morphology and intermediate forms of incompatibility between related strains (i.e., parent-offspring, half-sibs) suggests genetic control of histo-incompatibility and hyperplastic growth.