For this project, I asked the students to go out and photograph trees and plants. I stressed the importance of framing the leaves against a blank background (like the sky or a blank wall) so that they could really tell the difference between the positive and negative space. We then tweaked them in Picasa and printed them out as high contrast black and white photos.
Working from the photo of their choice, the students drew the outline of their plants/leaves. They then had to tear black paper into tiny pieces and glue it down to fill in the positive space that makes up their plant. Next, they printed out a few pieces of patterned paper that they then tore to fill in the negative space/background.