Xenobiotic growth refers to the phenomenon that secondary metabolites produced by plants inhibit the growth, development and elimination of other plants through information during plant growth. Based on the above definitions, Which of the following are not classified as:. ['Black walnut leaves contain walnut quinone, which can inhibit the growth of other plants.', 'The farmer sprayed the herbicide and killed the surrounding rice seedlings.', 'Apples and pears can release gaseous ethylene from fruits, branches and leaves, causing the surrounding plants to wither and fall early.', 'A hormone secreted by pine roots can inhibit the growth of birch.']