The acorn had ripened and ceased its growth. It no longer attracted sap through its base of attachment, and the latter consequently became dry and brittle. Possibly its feeding tubes were choked; at any rate, it is certain that it underwent a sort of death and was no longer able to keep the acorn in place. The process was much like that which occurs in the shedding of leaves, with, however, the very noteworthy difference that the acorn itself was still alive. We have not, however, done with our oak twig. The acorns which it bore were only appendages to an appendage, and it now becomes the turn of the cups themselves and the whole of the long foot-stalk on which they are mounted to become detached. These are no part of the tree, and are of no use to it. They were developed in order to bear flowers and fruit; that function they have now discharged, and they must die. Life is preserved only by the discharge of function, or at any rate the effort to discharge it. Utter inactivity leads to death, and death leads to separation from the living and to decay. You see that the whole foot-stalk is brown and shrunken and evidently dead. This condition ends abruptly where the foot-stalk joins the stem. At this spot, if you look carefully, you will see that there is a ring of constriction, marking definitely where detachment is in progress. This was the spot at which the production of the whole appendage began, and here a sort of joint was left at which the final detachment was destined to occur. Just one word of caution, that we must not carry our distinctions too far. After all, they are to some extent matters of degree. The joint which separates the appendage from the twig on which it is produced can hardly be termed a true joint, for certain structures run in unbroken continuity from the stem to the appendage. These are the fibro-vascular bundles by which the appendage is fed and also fixed in place. These bundles are usually quite visible in the scar-surface left when a leaf or fruit is broken off. They are “the nails in the horse-shoe” of the leaf-scar of the horse chestnut. Still, it is certain that a sort of joint is present, and that the structures are continuous in a very different sense from that of a stem or true branch. You may observe this difference in my acorn-bearing twig, for there are two acorn cups, and one has been produced by a branching out from the stem of the other. This little branch is smoothly continuous with the parent branch, and shows no preparation for detachment whatever.