1. The main reason is that pears produce ethylene, which is a kind of plant hormone substance with ripening effect; So when pears and persimmons are put together, the ethylene produced by pears will ripen persimmons and make them soft.

2. Ethylene is a compound consisting of two carbon atoms and four hydrogen atoms. Two carbon atoms are connected by a double bond. Ethylene exists in some tissues and organs of plants and is converted from methionine under the condition of adequate oxygen supply. Ethylene is the basic chemical raw material of synthetic fiber, synthetic rubber, synthetic plastics (polyethylene and polyvinyl chloride) and synthetic ethanol (alcohol), and it is also used to make vinyl chloride, styrene, ethylene oxide, acetic acid, acetaldehyde, ethanol and explosives, etc. It can also be used as a ripening agent for fruits and vegetables, and it is a proven plant hormone.