Lisa Marshall, age 9, of Santa Maria., California, for her question:

Are oak apples poisonous?

A so called oak apple has a strong., bitter taste. Besides, there is a wormy grub inside it. Sometimes a hungry squirrel breaks it apart and eats the whole thing. He does not mind eating a few wormy grubs and the bitter taste does not seem to bother him at all. Ages ago, people in Asia and Europe thought that anything that tasted so bad must be good medicine. So they brewed up oak apples to make tonics and also served it to patients who got themselves poisoned.

Eating a so called oak apple may not poison a person. But it certainly has a horribly bitter taste. What's more, not many people fancy eating the wormy grubs that are inside it. Ages ago, Andy decided not to sample anything growing in the wilds. For another thing, any wild plant may be infested with microbes and many of them are full of secret poisons. Even non poisonous mushrooms found growing in the wilds are likely to contain grubs or insect eggs.

So to be on the safe side, Andy either grows his own vegetables or buys them in stores where they have been inspected. When exploring the great outdoors, he prefers to admire the wild growing things    and to leave them where they belong. He says that this is safer for them and for him too.

An oak apple is really a gall and not really an apple at all. It is a round, woody ball fixed onto a twig or a leaf of an oak tree. It is caused by an insect    but nobody can explain how he does it. The story begins when a little Waspy insect seeks a place to lay her eggs. She chooses a certain oak tree and drills a small hole in a twig. Into this tunnel she places one tiny egg and` goes on her way. Soon the egg hatches into a grub. In some mysterious way the youngster forces the tree to grow a wad of woody cells. Soon he is safely inside an oak apple.

The hungry grub feeds on tree sap. His oak apple home is also a pantry filled with his favorite food. Sealed inside, he eats and eats until he reaches his full size. Then he becomes a sleeping pupa and changes into a winged insect. His oak apple now feels like a prison. So he eats himself a tunnel and climbs outdoors  ¬where he spreads his wings and flies away.

Dozens of other insects play tricks like this on different trees. Their mysterious galls may be large or small, on the roots or on plants above the ground. Some types infest goldenrod plants; others damage wheat crops. Not all galls are caused by insects. Some are caused by slime molds and bacteria.

Dyes from oak apples are used to tan leather, color cloth and imprint tatoos on the skin. One type is very special. It is used to make the ink to print treasury notes for the United States and the Bank of England.