ABSTRACT
When a hydranth is picked off the stolon another normally regenerates from the same spot.
When the nodal coenosarc is exposed to sea water the probability of hydranth regeneration is much reduced and stolons may grow.
A similar exposure of the coenosarc in the middle of an internode results in branch stolon growth at about the same frequency as at a node but hydranths do not grow.
Cutting the coenosarc does not affect the structure which grows, but where the stolon is cut at a node and a hydranth regenerates it does so at a distance of 0·3–0·6 mm from the node.
Grafting a hydranth into the side of the stolon at a node usually prevents hydranth regeneration but the inhibition ceases when the graft is made at distances greater than 0-3 mm from the node.
There is some evidence that hydranth regeneration is preceded by the development of a contractile growth region in the stolon.
A node has a latent morphogenetic capacity to enable hydranths to grow there, a capacity not demonstrated in the middle of an internode.
Local exposure to sea water reduces the morphogenetic capacity of stolon coenosarc for hydranth growth and increases it for stolon growth.
Hydranth growth may require the earlier formation of a contractile growth zone.
An existing hydranth usually inhibits the initiation of another hydranth at or close to its junction with the stolon, perhaps by preventing the formation of such a growth zone there.