Abstract
Visible response to injection of flower heads of perennial sow thistle plants with herbicidal concentrations of 2,4-D appeared only in the uppermost regions of the plants. The herbicide moved downward through peduncles supporting treated heads, then it moved upward through neighboring peduncles. Apparently this pronounced ascent of herbicide was associated with transport of plant solutions to regions of rapid development and transpiration.On the other hand, response to injection of severed stems of flowering sow thistle plants was not limited to the region of treatment. The herbicide moved downward in treated stems, upward in their intact lateral branches, leaves, and flowers, and extensively downward and laterally in the root system.Significance of this multidirectional movement is discussed.