If a stem is severed from its root system:.
a. branches at the cut end will become positively gravitropic in response to the loss of an auxin sink in the root. Their apical meristems will take on root meristem identity once they contact the soil, due to ethylene accumulation.
b. axillary buds near the cut end will take on root meristem identity due to the disruption of strigolactone transport, and, because root meristems are not repressed by apical dominance, they will begin to grow. the shoot will die because stems cannot produce new root meristems.
c. auxin traveling down through the stem in the phloem will accumulate at the cut end and trigger the initiation of root meristem.