In diameter, with little yolk, and the embryos provided with large trophic vesicles (Willey).
Held together by the adhesion of the cell-walls at the surface of Protosiphon and Botrydium, on the one hand, are minute vesicles contact.
A characteristic feature of the more massive species is the occurrence of air-vesicles in their tissues.
In Fucus vesiculosus they arise in lateral pairs; in Ascophyllum they are single and median; in Macrocystis one vesicle arises at the base of each thallus segment; in Sargassum and Halidrys the vesicles arise on special branches.
Other granules, easily mistaken for the " starch " granules, are also found in the cells of Phaeophyceae; these possess a power of movement apart from the protoplasm, and are considered to be vesicles and to contain phloroglucin.