Most people know that if you cut the tip off of a branch, the rest of the branches below it will grow stronger, giving the plant a 'bushier' look. This apical dominance is regulated primarily by the production of auxin in the terminal bud, which is translocated downward to the buds on the branches below it. By interfering with tryptophan synthesis, glyphosate interferes with the production of auxin, which reduces or eliminates apical dominance in a plant. At normal rates of application, glyphosate is not absorbed through dead bark cells. Bark that is dark gray or black has layers of dead cells between the exterior of the bark and the living cells inside.
Many woody plants have living cells in the outer bark when they are young.
These living cells are recognizable by the pigment in them. Maples, oaks, honeylocust, lindens, and many others all have green, yellow, or pink bark when young. Glyphosate can be absorbed into these living bark cells. It can then be translocated in the bark. The distance it is translocated depends on the thickness of the bark and amount absorbed.