Oh, those white things in the middle behind the boards are pipes with holes drilled in. Someone in the comments on that site suggested it, it helps get water all teh way to the plants on the bottom.
Dr. Seuss~DLH (brother's cat)~June 2007-
Misty~DSH (my cat & Mooby's mom)-?- Sept. 15, 2014
MooBoots(Mooby) ~ DMH(Mom's cat)~July 21, 2008-
Sunshine~ Golden retriever X white german sheperd (Dad's dog)~October 24, 2008-