Glue may work but only for a short time - I had a similar problem just a couple of weeks ago with a large 19" square plastic lid of a plant propogator - very badly cracked and split asunder - but still in one piece.
I bought some very expensive (£9 a roll) super strength Gaffer Tape - clear with white lines running along it.
I used it both on the inside and the outside of the lid - I also used some Super Glue but in truth the glue is doing nothing (all over my fingers and the kitchen worktop) - it's the tape that holds the thing rigid.
My tape came from a UK DIY store B&Q.
Good luck...
Peccavi, February 2010
