(12) Why is it that he says, “And in the fourth generation they shall return again hither?” (Genesis 15:16). The number four is more fit than any other number, for this reason, that as it is more perfect, and is the root and foundation of the perfect number ten; and it is according to the principle of the number four that all collected are to return hither, as he himself has said. But as he by himself is perfect, so also those of whom he is the father are evidently perfect. But what is it that I am saying? In the generation of animals the sowing of the seed has the first place; in the second place, comes the fact of each instrument being, in some manner, impressed by something akin to nature; thirdly, there is the growth after the first formation of the creature; fourthly, after everything else comes the perfection, that is to say, the birth. And the same principle and order prevail in plants; the seed is cast into the earth, then it pushes its way both upwards and downwards, partly in roots and partly in branches; after that it increases; and fourthly, it produces fruit; and in the same manner again the trees, when made, first of all produce fruit, which subsequently grows; then, as it becomes ripe, it changes colour; and, fourthly, and this is the last operation, it completes and perfects its work, the consequence of which is the use and enjoyment of it by men.