Question
My violets look fine on the top, but the lower leaves become limp and die.  This continues until the entire plant dies.  This only seems to happen to the violets that have smooth (not curly) leaves. My violets were blooming profusely, then suddenly started to die from the bottom up.  They are in a north window and had been doing well for several years.

Answer
Pat,  is it at all possible that you might have a disease or a fungal infection in your plants? The fact that is affecting all of your plants makes me suspect that. unfortunately, if it truly is a fungal infection the only treatment is to dispose of all of the affected plants. I know that is devastating! Look carefully at the leaves underneath the leaves to see if you can find any sign of insects. This can be treated  while fungal infections cannot be treated. Fungal infections spread to other plants that are nearby, and are really tragic and the outcome.  It sounds suspicious to me because you say they are all affected, and that it happened kind of suddenly after they were all flowering well. So, get a magnifying glass and look for some kind of little insects no matter how small, then go to the nursery store and purchase an anti-insect medication or spray.  If you cannot find any sign of an insect, whitefly, aphid or any kind of an insect then you can try pulling one of the plants out very carefully to examine its root system. If the roots appear to brown, soft, or a little mushy it certainly sounds like a fungus. If you need further help please let me know