The necessary beginning to our inquiry is a statement of the difficulties about these points.
Plants too have in some cases a long life, while in others it lasts but for a year.
Perhaps in the case of certain maladies a diseased state of the body and shortness of life are interchangeable, while in the case of others ill-health is perfectly compatible with long life. We find this distinction affecting not only entire genera opposed as wholes to one another, but applying also to contrasted sets of individuals within the same species. Races inhabiting warm countries have longer life, those living in a cold climate live a shorter time. Likewise there are similar differences among individuals occupying the same locality. Since fire and water, and whatsoever is akin thereto, do not possess identical powers they are reciprocal causes of generation and decay.