From the Royal Dairy Newsletter, "Royal Post", Longmont CO, Spring 1997:
The Tomato - A fruit or a Vegetable?
The Conquistadors discovered the tomato in Mexico in the 16th century. They returned to Europe with tomato seeds, and the tomato became very popular in Italy and Spain, but not in England. The British were convinced that tomatoes were poisonous. [ed. note: Tomatoes were known as "The deadly nightshade."]
In the 19th century, they became popular in this country when the Creoles in New Orleans used them in their delicious gumbos and jambalayas - convincing a doubtful population that they were a versatile and tasty vegetable.
However, the tomato is actually a fruit! The confusion exists because the Tariff Act of 1883 placed a 10% duty on all vegetables entering the country, but allowed fruit to enter duty free. The New York Customs Collector saw an opportunity to increase revenue and declared the tomato a vegetable.
Importers angrily sued and their case reached the supreme court where Chief Justice Horace Gray, speaking on behalf of the unanimous bench, ruled that "although botanists consider the tomato a fruit, tomatoes are eaten as a principal part of a meal, like squash or peas, (and all grow on vines), so it is the court's decision that the tomato is a vegetable."