Loretta Sharp, age 11, of St. Catharines, Ont., Canada for her question:

HOW MANY DIFFERENT TREES ARE THERE?

One would think that old Andy could report a definite answer to this simple question. Not so. Nobody has made an accurate one by one count of all the tree species that belong to the earth. No, this is not one of those mysterious Top Secrets. True, there are a couple of believable excuses. But, let's face it, this important job has been neglected.

Naturally several renowned plant experts were willing to make estimates. These educated guesses ranged from 20,000 to 50,000. The most thoughtful estimate, in Andy's opinion, was 40,000. However, our plant experts really are geniuses, forever working to produce new and superior species. Hence, if we knew exactly how many tree species exist now, the number would have  to be updated next year and each year thereafter.