Just some thoughts about the grain in curly wood:
Any wood can be curly. Most people think of maple but walnut, cherry, ash, or a lot of other woods can have curl.
The grain fibers in curly wood run the full length of the wood, just like wood without curl does, with one difference.
Rather than being straight like regular wood, the grain in curly wood grows in a wavelike manner.
Take a look at my sketch below and notice how the fibers weave back and forth.
People who have worked with wood know that the end grain on a board readily soaks up a stain and doing so always makes it darker than the wood on the face of the board. Keep this in mind as you read on.
Because the grain is wavy on curly wood, every place a wave in the grain is cut off as it meets the surface, a small amount of its end grain is exposed.
This exposed end grain absorbs the stain easily.
On a good piece of curly wood, this will make a dark stripe that is perpendicular to the actual grain of the board.
In the areas where the grain is running parallel with the surface, the wood absorbs the stain just like a straight grained wood does making this area look lighter.
This will make a light stripe of wood that is perpendicular to boards grain direction.
Because the actual end of a piece of curly wood is just showing its end grain, it will never look curly or striped.
Knowing this, one can see why a piece of curly wood is no weaker than a piece of straight grained wood.
It sure is more interesting to look at though.