To protect themselves from drying out, plants and trees drop their buds, blooms and leaves. For cut flowers and potted plants this dropping is often the result of over-production of the growth hormone ethylene; the only known gaseous, naturally occurring plant growth hormone. Ethylene gas regulates the ripening/ageing of cut flowers, potted plants, fruits and vegetable fruits. Ethylene gas is therefore purposely used to promote the ripening of fruit and the blooming of potted plants.