Creating a transparent gradient: Transparency tool not available
I'm trying to create a gradient that fades into an image, but all tutorials I've seen show an option in the gradient toolbar for a Transparency box to be checked. I have no such box. Where do I find it so that I can pull this effect off? Or is there a better/easier way to do it?
What I'm trying to do (you can see where the gradient line ends, which the client did and I'm trying to fix by rebuilding):

What my Gradient options bar shows (no Transparency checkbox):

What tutorials show (Transparency checkbox next to Dither):

