A system for measuring penetration of radioactive ions across roots of intact plants.

A technique was developed for estimating penetration of P(32) across roots of intact plants (Phaseolus vulgaris) by measuring the level of isotope in the xylem stream. Penetration was defined as movement from the root surface to the xylem sap. The xylem sap measurement for P(32) was made in the stem as the material ascended the plant in the transpiration stream. Stems were held near 0 degrees to arrest metabolic concentration of isotope adjacent to the xylem column. A 3 layer environment control system was constructed to allow stem chilling in a manner that would not interfere with the environments of the roots or foliage. Despite these precautions, some extra-xylary build-up of (32)P occurred in the chilled stem. The mathematical function of the extra-xylary fraction was derived, and the difference between this value and total P(32) in the stem represented xylem sap isotope.