That's why I am not answering anymore :no::laughing:. I will let someone else take a crack at it. I summed it up, its a deformity. Imaging the growing part of the tree as a sock like you are wearing. Your pant leg is the bark, your leg is the already mature heartwood. Pull the sock up tight and you have straight grain. Now scrunch the sock down and you have curly grain.Sorry,but one answer leads to 10 more questions.
What causes it, if anyone knew for sure there would be "curly maple" orchards. It cannot be bred, or reproduced or cultivated in a manageable way to produce curly stock. If it could it would not be so rare, it is a freak of nature.
I think you need to start from the basics, then maybe you can wrap your head around the unusual. Here is my homework for you. http://www.amazon.com/Understanding-Wood-Craftsmans-Guide-Technology/dp/1561583588
Maybe some of the others have good reference material suggestions to?