Yellowish pigments, or carotenoids, become visible as the green no longer masks them. Proteins and waste materials from this metabolic activity, is transported from the leaf. An abscission zone appears at the juncture that the tree rejects the leaf. Abscission cells form in the stem for the purpose of the tree to force the leaf off the tree. Within several days of receiving a hormonal message, abscission cells form: a narrow bumpy fracture line.