I am with you, father, with eyes and ears all open. I’ll tell you what it is, Willie, we shall have not only to be inside the tree, but to be able to stay there a few weeks or months to notice all. That is easy enough. We may as well fancy hundreds of years as millions of miles. Let us go to the pith. Around here are vessels in the sheath of the pith. The circles of wood are ranged outside. We will pass along one of the Medullary or pith rays, which you saw make the silver lines of the wood, and here we are at the Liber or inner bark. But what is this soft white wood next to it? This is the _Alburnum_, or white wood. When you tap a tree, the sap comes from this part. Now watch what is coming. I see--the Liber is separating from the soft Alburnum, and there comes a sticking substance of sap oozing between them. What is that? It is the _Cambium_, or _Albumen_; the white of egg is albumen. Look again. Ah! the cambium is softening the cellular tissue that bound the liber to the alburnum, and while that is growing outward, I find that the other parts are growing upward. Let us take a peep at the leaf buds. You see they feel the growing influence, and are letting fall bundles of woody matter, which pass into the cambium, and become attached to the liber. The cellular tissue passes in the mass around, along the medullary rays, and a new substance becomes attached to the liber. But that new substance is another alburnum, father, and our old alburnum is turned a quite hard wood. You see, then, that while the last year’s soft wood becomes a hard ring or layer, another is formed in its place alongside of the liber. The hard wood is dead compared with the softer kind. I think I understand that. But where does the nourishment come from? The sap when first rising is watery and nearly colourless. But after exposure to air and light in the leaf, and losing much water in evaporation, it becomes thicker, and, descending by the bark, is prepared, like blood, to renew and to form different parts of the structure. Is there any other movement of the fluids of a plant? Yes, there is a true circulation in the interior of all the cells. Does a tree form a fresh ring of wood every year? This depends upon the character of the tree. Some trees take many years in forming it. How is it that the layers of our Gum tree are not equal in thickness? That is influenced by the season. One year it was very cold or dry, and the tree made little wood. Another season, the rain was abundant, and the sun did his work well, and so the _concentric_ or ring-like layer was fuller. But I see that on one side of the tree, the bands are thinner than on the other. That was the side that received the cold wind. The greater the number of leaf-buds above a part of a stem, the greater the diameter. How does the bark manage when the tree forms new wood, and presses against the liber?