Richard Leuthauser, age 9, of Sauquoit, New York, for his question:

Why cannot oaks and elms be tapped for syrup?

Chances are, you can list the names of 20 different trees. If you decide to study the world's trees, you will learn the names of many hundreds of them. And every type of tree is different from all the others, especially in the small details. Trees, of course, do not have red blood like ours to carry nourishment to their boxy cells. This work is done by sap, and every type of tree has a different kind of sap. The sap in a Christmas tree is tacky and it has a fresh smell, somewhat like tar. This pine tree sap has a lot of gummy resin. It helps to seal out the cold so that the tree can stay green through the winter.

One tree that grows in the tropics has a milky, rather gummy sap. We drain off its sap and treat it to make rubber. This rubber tree has several cousins with rub¬bery sap that is not quite so useful. Oaks and elms have watery sap with hardly enough sugar to taste. All our lovely maples have slightly sugary sap. But one and only one has the right kind of sap for making maple syrup. In early spring, the sap of the sugar maple is so rich that we can use it to make thick syrup and a wide assort¬ment of sugary candy.