But in cold countries the humidity in animals is more of a watery nature, and hence is readily congealed. Water animals have a shorter life than terrestrial creatures, not strictly because they are humid, but because they are watery, and watery moisture is easily destroyed, since it is cold and readily congealed. For the same reason bloodless animals perish readily unless protected by great size, for there is neither fatness nor sweetness about them. Further they have an oiliness and a viscosity which makes them retain their moisture in a form not easily dried up, even though they are dry and earthy. But we must discover the reason why trees are of an enduring constitution, for it is peculiar to them and is not found in any animals except the insects.
Plants continually renew themselves and hence last for a long time.
New shoots continually come and the others grow old, and with the roots the same thing happens. But both processes do not occur together. Rather it happens that at one time the trunk and the branches alone die and new ones grow up beside them, and it is only when this has taken place that the fresh roots spring from the surviving part. Thus it continues, one part dying and the other growing, and hence also it lives a long time. There is a similarity, as has been already said, between plants and insects, for they live, though divided, and two or more may be derived from a single one.