Except where it is terminal it arises, like the leaf-shoot, in the axil of a leaf, which is then known as a bract.
In the male flower the receptacle is "concrescent" or inseparate from the bract in whose axil it originates.
Thus a bract may be regarded, with Haeckel, as a modified umbrella of a medusa, a siphon as its manubrium, and a tentacle as representing a medusan tentacle shifted in attachment from the margin to the sub-umbrella; or a siphon may be compared with a polyp, of which the single tentacle has become shifted so as to be attached to the coenosarc and so on.
Their cones are composed of thin, rounded, closely imbricated scales, each with a more or less conspicuous bract springing from the base.
The female flower consists of a cup-like receptacle, inseparate from the ovary, and bearing at its upper part a bract and two bracteoles.