Berldy, jasmindudic: Wood grows to the sides of the tree trunks. Trees grow by putting seeds on top of wet soil while having enough space above. Xpand multiplies the touching elements when receiving power.
Well, update! Have fun playing Bach in The Sandbox. Also, I still have to find a way to update the save system to save note frequencies and such. You'll have to tune them by hand, although I'll work on it today.
@petso66: Because it's faster to check only for seed-wet soil contacts than to check for water-touching-soil-with-a-seed-underneath. Also, because it's much more common to have lots of water than lots of seeds and I rather check only for the few seeds than for all the water pixels you people love to draw :)
 "The Sandbox")
 "SandTest")