Stamp of the day: birch wood

Yesterday I was teaching about plant anatomy, about the cells and structures inside plants that make plants work and make them alive.  Wood is an amazing thing, made up from lignified plant cells that become hard, sturdy, and dead and can hold up giant trees through snowstorms and summer rains. Wood is dead xylem, the part of the vascular tissue that transports mostly water up into the top of the plants.  The yearly rings in wood from temperate regions are because the xylem made in spring are made from large diameter cells, lots of water is needed then.  In the summer and fall, then the xylem cells are smaller, and the tissue becomes tighter and darker, and you get the dark band for that year. 

Here are some fantastic photos of plant anatomy, and this Swedish stamp show wood from birch, which you can of course use for firewood.