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Plants of wheat, ryegrass, red clover, white clover, and N eptunia amplexicaul'is (a selenium accumulator) were grown in nutrient solutions containing 75Se-selenite ion. The uptake of 75Se was measured and the root and shoot tissues fractionated to examine the products of selenite assimilation.Over a period of 10 days the uptake of 75Se-selenite from culture solutions was of a similar order (expressed per gram fresh weight) for all five species.Characteristic differences were observed between species in the distribution of 75Se in different fractions. The highest ethanol-soluble concentration of 75Se was found in N eptunia, in which at least two unidentified seleno-compounds were present in appreciable amounts. Selenite was predominant in the ethanol extracts of wheat, whereas those from the pasture species contained selenium analogues of several common sulphur-containing metabolites.An appreciable unidentified fraction was present in ryegrass extracts.Aqueous extracts made after alcohol extraction contained selenite, as well as material which was immobile in chromatographic and electrophoretic systems and was probably elemental Se.Extensive protein incorporation of 75Se in seleno-amino acids was observed in ryegrass, wheat, red clover, and'white clover. Protein incorporation of 75Se occurred to a much smaller extent in N eptunia.

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