gittin 22

plants with no roots in the ground

and people who cannot understand what they are writing.

a get (divorce document) can only be written on something that is detached from the ground. it is discussed if a plant in a perforated pot is considered detached or attached. also on this page is the mishna that outlines that anyone can write a get, including imbeciles, deaf-mutes and minors. people who are usually not considered halachically capable of understanding.