The polarity of movement of gibberellin through sections cut from near the root tips of Zea mays L. was studied, using methods like those we previously used in roots for auxin and in petioles for auxins, cytokinins, and gibberellic acid (GA-3). One IJ-g GA-3 was added in a donor agar block and gibberellin activity in the receiver agar at the opposite end of the section was measured directly with a modified barley endosperm bioassay. The movement of gibberellin was away from the root tip (basipetal) and thus opposite in direction to the polarity of auxin through such root sections. The time-course of basipetal movement was dissimilar to that for gibberellin or auxin movement through petiole sections. It took 14-18 hr for gibberellin activity equivalent to 6 ng GA-3 to collect in the basal receivers on roots. Apical receivers showed activity equivalent to 1.6 ng GA-3 at 14-18 hr. Less than 0.01 ng equivalent GA-3 was collected from sections to which GA-3 was not added, so the 6 and 1.6 ng were almost entirely due to the added GA-3. These general conclusions were confirmed with an experiment using 14C-GA-3. A decline in activity in receivers was found in some experiments at 18 hr, paralleling earlier results with GA-3, IAA, and adenine in petioles and IAA in roots.

The polarity of movement of gibberellin through sections cut from near the root tips of Zea mays L. was studied, using methods like those we previously used in roots for auxin and in petioles for auxins, cytokinins, and gibberellic acid (GA‐3). One μg GA‐3 was added in a donor agar block and gibberellin activity in the receiver agar at the opposite end of the section was measured directly with a modified barley endosperm bioassay. The movement of gibberellin was away from the root tip (basipetal) and thus opposite in direction to the polarity of auxin through such root sections. The time‐course of basipetal movement was dissimilar to that for gibberellin or auxin movement through petiole sections. It took 14‐18 hr for gibberellin activity equivalent to 6 ng GA‐3 to collect in the basal receivers on roots. Apical receivers showed activity equivalent to 1.6 ng GA‐3 at 14‐18 hr. Less than 0.01 ng equivalent GA‐3 was collected from sections to which GA‐3 was not added, so the 6 and 1.6 ng were almost entirely due to the added GA‐3. These general conclusions were confirmed with an experiment using 14C‐GA‐3. A decline in activity in receivers was found in some experiments at 18 hr, paralleling earlier results with GA‐3, IAA, and adenine in petioles and IAA in roots.