Father, what are these silver lines through the solid wood, coming from the pith centre?

They are the medullary or pith rays, and reach the liber or inner bark. They convey nourishment. Through them there is also a communication between the root and the leaf.

I want to ask a question about the leaf. Does it throw off anything as well as absorb?

You have been told that it absorbs oxygen from the air, and also carbonic acid gas—that is, carbon and oxygen. This carbonic acid floating in the air is absorbed in the day-time, though the leaf exhales, or breathes out, oxygen gas while the sun shines.

Does it not do so at night?

No; then the leaf throws out some carbonic acid gas undigested. There is this use of the oxygen being taken in by the leaf, that it acts beneficially upon the sap to thicken it, &c.

What is the true shape of the leaf?

The course of veins or branching vessels. The fleshy part of the leaf is of cellular tissue.

I have heard that our leaves differ from English ones: how are they different? I know they do not fall off in autumn.