Abstract
The duckweed Spirodela oligorrhiza was cultured at both pH 5 and 7·2 in sterile nutrient solutions containing 75Se-labelled selenite or selenate. At both pH values, selenite was absorbed and assimilated about three times more readily than selenate_ Colloidal selenium-75 at pH 7·2 was also investigated and found to be metabolized to a considerable extent. The labelling patterns observed were very similar for all three inorganic forms of selenium, with a predominance of selenomethionine incorporated into proteins.