Vent hose??

Hi...i have a mariner 115....1993...out of the lower unit, or just above it is a small hose. it just kind of sticks up out of the water line near the outboard and is plugged..i just moved, and my shop manual is in storage so i cant look it up....i want to go out this weekend but that hose got cut somehow. does anyone know what it is...and can i just plug it with anything and be safe? Here is a pic of the hose. Thanks