Control group for sound wavelength germination experiment

[Craig Galbraith]

I am wondering if anybody out there can help me...

I am designing an experiment on the effects of two different wavelenths 
on the germination of Pinus banksiani seeds (Jack pine).  I will be 
presenting two tones of different wavelengths to 5 and 5 petri dishes
of seeds.  The problem is:
	how should I set up a control group?

I am thinking along the lines of a plastic shield, but I'm not too sure
if that will suffice.

Any help would be greatly appreciated.

Craig Galbraith
University of New Brunswick, Saint John
j5oa at jupiter.sun.csd.unb.ca