You start with a cardboard tree, set it in water and watch as the water is absorbed (Oh! Good demonstration for a chemistry class, no?). 15 - 30 minutes later crystals start to grow on it. 5 - 6 hours later, it's covered! I googled and found a neat PDF by a David A. Katz that's a great help in understanding what's happening and what the crystals are.
From the PDF:
The blue-green colored powder consists of an alkaline salt, an ammonium salt, and water. A representative solution (but not the exact Magic® Tree formula)can be made from 6 tbsp. sodium chloride (not an alkaline salt), 1 tbsp. ammonia, 6 tbsp. water, and 6 tbsp. liquid laundry bluing (such as Mrs. Stewart’s Liquid Bluing ). In operation, the solution moves up the tree by capillary action. The tree is permeated by the solution, however,the branch tips, being tapered to a point, experience the most rapid rate of evaporation resulting in crystal formation. (NOTE: tbsp. = tablespoon)
We grew one at my parent's house and then bought more to bring home and to tuck into the neice and nephews Christmas gifts. Another one is growing as I type.
Since you're going to be buying the Evolution popup book I plugged a few days ago anyway you might as well order the Magic Tree as well.
Here's the handy link you'll want to use for the purchase - Magic Tree by Schylling
I'm pushy aren't I? But heck, I want some Amazon gift certificates. :)
Our neat moment for today was when the cat came in with a burdock nestled in the fur on his back.
We took it off, stuck it to each other and dissected it to get a good look at the seeds. Then we talked about how it stuck to everything and what that adaptation meant in terms of how burdocks spread. Neat stuff.