"The blindness of those who think it absurd to suppose that complex organic forms may have arisen by successive modifications out of simple ones becomes astonishing when we remember that complex organic forms are daily being thus produced. A tree differs from a seed immeasurably in every respect... Yet is the one changed in the course of a few years into the other: changed so gradually, that at no moment can it be said — Now the seed ceases to be, and the tree exists."