Abstract: Light and electron microscopy were used to study the involvement of phenolic compounds in the early development of the Northern Hemisphere fucoids, Fucus serratus (L.), Fucus spiralis (L.) and Himanthalia elongata (L.) S. F. Gray. Phenolic compounds, packaged within physodes are a major cytoplasmic component of brown algae. Physodes accumulate at the zygote periphery early in development and are secreted into the primary zygote wall. At germination, physodes accumulate at the rhizoid tip. Physodes, together with other wall components, contribute to the development of the cell plate. Good evidence already exists for the involvement of phenolic compounds in the development of Southern Hemisphere fucoids, and this study shows that phenolics play a similar role in the Northern Hemisphere. Consequently, their perceived role as herbivore deterrents in Northern Hemisphere species may be a consequence of their role in wall construction.