It is normal. I actually cut all the bottom leaves that touch the ground soon enough after transplanting, when new grows started and bottom leaves start to turn yellow. They do not get enough sun when new leaves open up, so plant stop feeding them. And as soon as you cut them plant starts grow more new leaves.

how old.. how big?? soil??? whats the weather been .. drought or torrential rains ???? what are other trees in the 'hood' doing... other trees stressed? more facts will give a better answers ... ken

I had precisely the same situation: a store-bought plant that was doing great for a while under fluorescent light (a CFL in a gooseneck lamp), then the lower leaves started yellowing, showing spots, etc. I took a really close look under a low-power microscope, and found out I had mites. These little suckers are nearly transparent, unlike the black ones that are relatively easy to spot. I believe that the plant cuts off nutrients to the infested leaves as a defense mechanism, since the mites can't suck the juices from a dry leaf. Use a miticide if you're OK with chemical treatments; Bayer's 3-in-1 has a particularly effective agent in it. If not, or if your state hasn't approved the stuff for sale (you cannot buy it in NY), you can try my approach: fill a bucket with soapy water (dish detergent, ca. 1/2 tsp per gallon), and shove the entire plant, upside-down, into the water. Slosh it around, and up-and-down, for about a minute. This removes the bugs, drowns the ones who won't let go, and I think it might even damage the eggs (tiny white specks on the bottom of the leaves.) Repeat once a week for at least 3 weeks (the mites have a 10-day life cycle), and maybe once a month after that to keep 'em down. The mites prefer a dry environment, so this treatment, along with misting, will prevent them from doing noticeable damage. I think the real problem with keeping these plants indoors is that the mites are not exposed to their natural predators, so their population can explode very quickly. They are incredibly persistent, and they will keep coming back time and time again if you don't manage to kill off every last one of them (and every last egg as well!) Unless you like having ladybugs crawling around the house, you're stuck with regular washing, or chemical treatments, to keep them under control. Here is a link that might be useful: Article on Spider Mites

Can you post a photo of the plant and tell us more about your water, fertilizing, and pest management regimen? Based on the information so far the problem could be any number of things. There several different disease possibilities each with their own cause and treatment but the odds favor other causes before jumping to the "must be a disease" conclusion. Dave