ABSORPTION AND MOVEMENT OF RADIOPHOSPHORUS IN BEAN SEEDLINGS

Preliminary results using the radioactive isotope of phosphorus (P32) as a tracer atom in Red Mexican beans (2) demonstrate the value of the method and its general application to plant physiological problems. Wherever it is desirable to follow the path or metabolism of single atoms, this procedure will prove extremely valuable. The equipment used for the detection and measurement of the radiophosphorus consisted of a NEHER-HARPER high speed Geiger counter circuit (14) in connection with a direct-reading counting rate meter for random pulses as designed by GINGRICH, EVANS, and EDGERTON (5). A Geiger counter tube with a very thin glass window (4) proved satisfactory. The samples to be measured were held in cellophane cones which in turn were suspended in the concave sensitive area of the counter tube. Only a relatively small percentage of the total beta radiation emitted by the radiophosphorus entered the cathode cylinider of the counter tube; however, the geometric conditions remained constant for all determinations, and the counts per minute recorded represent a constant percentage of the total emanation. Results represenit comparative amnounts rather than absolute quantities. The radiophosphorus was obtained through the courtesy of Dr. E. 0. and Dr. E. H. LAWRENCE, of the Division of Radiation, University of California. It was made by bombarding 8-million volt deuterons against red phosphorus, which in turn was converted into sodium phosphate. The radiophosphorus-containing nutrient solution was made as follows: