Depends, what kind of lines? It is possible to create vertical lines of arbitrary size using missiles or the ball; also, since it uses the standard kernel, it should be possible to change the background blocks on the fly, though there are no blocks implemented for that, yet.
I see. AFAIK, Pitfall uses the ball for implementing the vine; unfortunately, batari Basic does not support custom slopes for the ball; it is always drawn as a vertical line.