Photo of a leaf taken at Brookhaven National Laboratory, Upton, New York, after radioactive phosphorus 32 had been taken up by a Coleus plant. P 32 accompanies ordinary phosphorous food through the veins of the leaf. After the leaf has been placed against photographic film, the film is developed. Beta rays emitted by the P 32 leave light traces against the dark outline of the leaf as a whole. Photos of this kind can shed light on the concentration of phosphorous necessary to maintain a healthy plant under various conditions. The radioactivity pinpoints the take-up, and use, of phosphorus as food in different parts of a plant.