best flowers for growing in a wall

Need a better description of the location you want to grow in - you say "in" a wall - is it drystone, no soil, is it double walled with soil in the mid section, how big is it, do you just want low growing stuff?

How about Valerian ( aka kiss-me-quick) that's a good hardy one that seems to happily live in/on walls.

We have a low brick wall at the front of our house with some soil filled in - I'm determined to plant more wallflowers in it next year, well, i've already sown seed in a tray so have tiny plants and will plant out soon/end of summer for Spring flowering hopefully. They have a great scent and last awhile too. The ones I have are not perennials though.

Otherwise - Aubretia (mauve), and another one beginning with s, name escapes me! If I remember I'll pop back later... ha, Saxifrage!