Abstract
The composition and significance of physodes, brown algal subcellular bodies characterized by reactivity with vanillinhydrochloric acid, have been the subject of debate for the past century. This research is critically reviewed, and it is demonstrated that although physoides are primarily composed of phloroglucinol derivatives, they may contain other tannins and terpennes. The recent discoveries of homologous series of phloroglucinol polymers in brown algal extracts provide an attractive chemical rationalization for the observed heterogeneity of physodes.