The terms stress and stress resistance are used in the same way for plants as for man and other animals. Stress (= State of tension) signifies the effects of a “load” on the organism, caused by the influences of external factors (stress factors) which lead to an impairment or reduction in metabolism or development. The difference between stress and a stress factor is, in general parlance, frequently ignored; in the following we will always use the term stress in the sense of a complex syndrome produced in the organism by one or more stress factors.