I recently saw an interesting microscope photo in an endgrain slice of spruce, nicely showing the structure. To my surprise, this was visible with a good magnifier too, and even through a “supermacro” photo. Subsequently I could take a couple macro photos trough the magnifier, getting even closer.
They could have looked a lot better if the wood was cut cleaner. I used a well sharpened knife but the key is to cut thin and slow, but I still pushed too quickly.
You can see that the “grain lines” have pretty much the same cellular structure as the fast growth, just that they are packed tightly and the cells appear to be closed. I suspect there is a high content of resin in the area, which gives the dark color and “cements” it. We all know how it feels to press a nail in a dark line (doesn’t really work, but in between, it goes all the way down).
Each dark line seems to act as a brace then.
I am wondering whether the fast growth areas correspond to the spring period when the tree produces new needles?