I'm officially calling this post misinformation. See the text of the opinion (emphasis mine). They literally say "Botanically speaking, tomatoes are the fruit of a vine". This is not about whether a tomato is a fruit or a vegetable according to specific botanical or common definitions, but about which definition to use for the purpose of the Tariff Act of 1883. It doesn't say that tomatoes are a vegetable. It doesn't say that botanically they aren't fruits. It says that for the purpose of the Tariff Act of 1883 they are vegetables, not fruits.
Nix v. Hedden, 149 U.S. 304 (1893)
[...]
MR. JUSTICE GRAY, after stating the facts in the foregoing language, delivered the opinion of the Court.
The single question in this case is whether tomatoes, considered as provisions, are to be classed as "vegetables" or as "fruit" within the meaning of the Tariff Act of 1883.
The only witnesses called at the trial testified that neither "vegetables" nor "fruit" had any special meaning in trade or commerce different from that given in the dictionaries, and that they had the same meaning in trade today that they had in March, 1883.
The passages cited from the dictionaries define the word "fruit" as the seed of plaints, or that part of plaints which contains the seed, and especially the juicy, pulpy products of certain plants covering and containing the seed. These definitions have no tendency to show that tomatoes are "fruit," as distinguished from "vegetables" in common speech or within the meaning of the tariff act.
There being no evidence that the words "fruit" and "vegetables" have acquired any special meaning in trade or commerce, they must receive their ordinary meaning. Of that meaning the court is bound to take judicial notice, as it does in regard to all words in our own tongue, and upon such a question dictionaries are admitted not as evidence, but only as aids to the memory and understanding of the court. Brown v. Piper, 91 U. S. 37, 91 U. S. 42; Jones v. United States, 137 U. S. 202, 137 U. S. 216; Nelson v. Cushing, 2 Cush. 519, 532-533; Page v. Fawcet, 1 Leon. 242; Taylor on Evidence (8th ed.), §§ 16, 21.
Botanically speaking, tomatoes are the fruit of a vine, just as are cucumbers, squashes, beans, and peas. But in the common language of the people, whether sellers or consumers of provisions, all these are vegetables which are grown in kitchen gardens, and which, whether eaten cooked or raw, are, like potatoes, carrots, parsnips, turnips, beets, cauliflower, cabbage, celery, and lettuce, usually served at dinner in, with, or after the soup, fish, or meats which constitute the principal part of the repast, and not, like fruits generally, as dessert.
The attempt to class tomatoes as fruit is not unlike a recent attempt to class beans as seeds, of which Mr. Justice Bradley, speaking for this Court, said:
"We do not see why they should be classified as seeds any more than walnuts should be so classified. Both are seeds, in the language of botany or natural history, but not in commerce nor in common parlance. On the other hand, in speaking generally of provisions, beans may well be included under the term 'vegetables.' As an article of food on our tables, whether baked or boiled, or forming the basis of soup, they are used as a vegetable, as well when ripe as when green. This is the principal use to which they are put. Beyond the common knowledge which we have on this subject, very little evidence is necessary or can be produced."
