David B. Mayrose, age 13, of Sioux City, Iowa, for his question:

Is the tomato a fruit or a vegetable?

This tantalizing problem has been known to disrupt the processes of human digestion. It tends to crop up at mealtime. Members of the family often take firm positions on opposite sides of a heated argument when the digestive system calls for a more amiable emotional climate.

According to Andy's mail, almost everyone gets into this argument sooner or later. If you take a firm stand that the tomato is a fruit because it bears the seeds of the tomato plant, you are correct. However, if you state adamantly that the tomato is a vegetable because it is meant to be eaten as a vegetable course, you are also quite correct. This' two sided quality suggests that the argument may be somewhat subtle.

Those who want to seek a decision in a higher court could call in a number of qualified experts to support either side of the case. All the biologists, in the role of experts, would claim that the tomato is a fruit. They would be supported by botanists, ecologists, geneticists and a host of experts in other branches of biology. In scientific terms a fruit is the part of a plant which contains the ripening seeds, and, as a scientist, every expert would have to claim that the tomato is a fruit.

A normal scientist, however, is also a human being with an everyday life like the rest of us. In this role he might be inclined to agree with another group of experts who claim that the tomato on the table may quite properly be called a vegetable. These are the semanticians,.lexicographers, perhaps a phonetist and other language experts..

The lexicographer, who creates dictionaries, would offer several meanings suitable for different occasions for both fruit and Vegetable. One meaning of the word vegetable may be applied to any part of a plant used as an item of human diet. The semantician stresses the precise meaning of words and the problem of making oneself understood. These experts would state that the stewed or salad tomato is a vegetable.

The phonetist could not settle the argument either way, and he might give rise to another one. He is an expert on pronunciation, and on this topic he offers us a choice. We may call this fruit or vegetable a tomayto or a tomahto. The preferred pronunciation in our country, however, is a tomayto, and it is the one most likely to be understood at the supermarket.