Physodes are membrane bound, spherical bodies containing phlorotannins. They stain black with osmium, blue with Toluidine Blue O, red with neutral red, orange with fast red GG and are autofluorescent under violet and UV excitation (Clayton and Ashburner 1994; Schoenwaelder and Clayton 1998a, b; Schoenwaelder 2002a). Small light refracting bodies (probably physodes), were first described many years ago by Nägeli (1847) and Rosanoff (1868) (see Ragan 1976). Since then, many others have described them by many different terms including, brown algal bodies, fucosan granules and tannin bodies. It was Crato (1892) who first used the term physode, to describe the typically round to elliptical, mobile, vesicle-like, strongly light refracting bodies that he observed in cytoplasm of brown algae and other algae (Schoenwaelder 1996; Schoenwaelder 2002a). Brown algal physodes are vesicles containing predominantly phenolic compounds, specifically phloroglucinol and derivatives of phloroglucinol (Ragan and Glombitza 1986). Brown algal polyphenolics, occurring in a single structural class-the phlorotannins, are thought to be synthesized via the acetate-malonate pathway (Targett and Arnold 1998). Their chemical structure has been investigated in many species of brown algae (Glombitza and