Actually what is missing there in that vent line is a vent valve..it appears it has broken and fallen out. The missing piece is a two way poppet valve that fits in the space between the open line you see and the spiggot coming out of the tank. Those old plastic bits will need to be removed to install the new valve. The line you see goes up to the carbon cannister under the driver's side fender. It allows fumes to be drawn up into the carbon cannister, or conversely allows fresh air(through another valve) back into the tank to replenish the volume as needed. No surprise you are having fume problems.

You might get away with just an elbow instead of the vent valve...I have done this while tracing the cause of fumes in a different car with the same basic fuel system.