[plt-scheme] Memory / Garbage Collection

Can someone describe how the garbage collector works?  I saw in the
documentation that it's "conservative" but I don't know what that means
exactly.  I'm guessing that it doesn't handle structures that "point to
themselves".  I'm developing a genetic programming tool (which generates a
lot of temporary data) and I have a memory leak.  I'm using the Windows
version 202.

When I monitor how much memory Dr. Scheme uses, it starts off at 30M, and
continues to climb (sometimes in large 'clumps').  I am, to the best of my
knowledge,  releasing all references to the data structures.  In fact, the
memory stays allocated even when I click "execute", which seems like it
starts a totally fresh copy of the interpretter.

Also, I've tried to run the procedure (dump-memory-stats), but it doesn't
seem to do anything (it just grinds for a minute), not producing any output.

Can someone offer some advice?  Thanks, -Zach