Gr 4-6 Like Birnam Wood at Dunsinane, instant forests spring up every December in vacant lots, churchyards, and parking areas, and in the scramble to find the ``perfect'' tree, one scarcely has time to wonder at their source. Patent has taken that time. She tells of the historical origin of the custom of Christmas trees, the gradual shift from ``wild'' to ``farmed'' trees, and provides a detailed look at a tree farmer's year of work. A closing chapter tells about the varieties of trees on the market. Numerous color photos brighten the literary landscape. This is for older readers than David Budbill's Christmas Tree Farm (Macmillan, 1974; o.p.), which has a picture book format and considerably less detail. Patricia Manning, Eastchester Pub . Lib . , N.Y.