To become more familiar with the conception of the ur-plant, let us bring the life-cycle of the plant before our inner eye once again. There, all the different organs of the plant-leaf, blossom, fruit, etc. – appear as the metamorphic revelations of the one, identical active principle, a principle which gradually manifests itself to us by way of successive heightening from the cotyledons to the perfected glory of the flower. Amongst all the forms which thus appear in turn, that of the leaf has a special place; for the leaf is that organ of the plant in which the ground-plan of all plant existence comes most immediately to expression. Not only do all the different leaf forms arise, through endless changing, out of each other, but the leaf, in accordance with the same principle, also changes itself into all the other organs which the plant produces in the course of its growth.