title: An ultrastructural study of homoclonal and heteroclonal encounters between stolons in Podocoryne carnea M. Sars (Hydroidea, Athecata).
abstract: The various phases of homo- and heteroclonal encounters between stolons of Podocoryne carnea M. Sars have been studied with the light and electron microscope. The first clone-unspecific actions and reactions to an imminent encounter between the outgrowing tip of stolon and the subterminal part of an opposed homologous organ consists in a thickening of the ectoderm of both opponents. Presumably by enzymatic means the "attacking" stolonial tip dissolves the cuticular periderm of the "attacked" stolon, which in turn counteracts by synthesizing new periderm at the site of contact. In homoclonal encounters this counteraction is overcome by the lytic efforts of the advancing tip such as to allow it to anastomose with its opponent. In heteroclonal encounters, however, the periderm secretion enacted by the "attacked" stolon successfully counteracts the lytic activities of the "attacking" tip which eventually desists from its efforts and proceeds by moving over or alongside its reluctant opponent without having produced a fusion. In no cases is the recognition of "self" or "non-self" a consequence of direct contacts between cellular surfaces. The information, of still unknown nature, must in this instance be exchanged across the cuticular periderm which covers the stolons.
mesh_terms: D000818:Animals; D002450:Cell Communication; D002999:Clone Cells; D006829:Hydra / Q000254:growth & development / Q000648:ultrastructure*; D008854:Microscopy, Electron