In Dictyota, Sphacelariaceae and Fucaceae there is a definite apical cell.
Large coarse algae, such, for instance, as the Fucaceae and Laminariae, do not readily adhere to paper, and require soaking for some time in fresh water before being pressed.
Algae of more delicate texture than either Fucaceae or Laminariaceae also occur in the region exposed by the ebb of the tide, but these secure their exemption from desiccation either by retaining water in their meshes by capillary attraction, as in the case of Pilayella, or by growing among the tangles of the larger Fucaceae, as in the case of Polysiphonia fastigiate, or by growing in dense masses on rocks, as in the case of Laurencia pinnatifida.
In Fucaceae and Laminariaceae the inner tissue is differentiated into a conducting system.
Among Phaeophyceae it is well known that the oospore of Fucaceae germinates directly into the sexual plant, and there is thus only one generation.
The vesicles of Fucaceae and Laminariaceae prevent the sinking of the bulkier forms. But why certain Fucaceae favour certain zones in the littoral region, why certain epiphytes are confined to certain hosts, why Red and Brown Algae are not better represented in fresh water or Green Algae in salt, - these are problems to which it is difficult to find a ready answer.
In Fucaceae an apical cell is situate at the surface of the thallus in a slit-like depression at the apex.
Dictyotaceae resemble Fucaceae in their pronounced oogamy.