My last column talked about how to grow and shape the perfect Christmas tree, taking it from a small plant to the centerpiece of a holiday celebration. But what about the tree itself?High value is placed on needle retention and an evergreen smell to get revelers through four-plus holiday weeks. Thus, people often select a Balsam or Fraser fir. I'd like to throw another name in the hat - or forest: the Canaan fir (pronounced "ka-nann" with emphasis on the last syllable).