This sample is a cross section through wood from a type of oak (Quercus pubescens).
The video first shows “late wood”, which is formed towards the end of the tree’s yearly growth phase, then you can see the growth ring boundary, which is followed by an area with large holes. These large holes are pores that the tree uses for water transport between the root system and the tree top/ branches. They are characteristic for “early wood”, which is formed early during the growth season.
The slide was prepared by cutting the wood into very thin slices using a machine called a sliding microtome (essentially a very precise knife). Next, the slices were stained with two dyes – Safranin and Astra Blue. Astra-blue stains cellulose* blue (in the absence of lignin**). Safranin stains cell nuclei and cell walls containing lignin red (highly lignified wood fibers may appear pink).
*Cellulose is a polysaccharide – a complex sugar – deposited in the cell walls of plant cells.
**Lignin is an organic polymer that is present in all woody plants and gives them rigidity.
Here is a link to a book on plant anatomy that we found useful: http://www.forstbuch.de/SchweingruberCrivellaroWEB.pdf
The specimen was kindly provided by Elisabeth Wächter.