Collier's New Encyclopedia (1921)/Apple
APPLE, the fruit of the pyrus malus, a species of the genus pyrus. All the different kinds of apple trees now in cultivation are usually regarded as mere varieties of the one species which, in its wild state, is known as the crab tree, pyrus acerba. The Romans are said to have had 22 varieties of the pyrus malus, or cultivated apple tree. At the present time it is, perhaps, the most widely diffused and valuable of all fruit trees. About 1,000 varieties are cultivated in the United States, where the cultivation of the fruit on an extensive scale has become one of the most profitable industries.
The apple is regarded by botanists as the type of the kind of fruit to which they have applied the term pome. The eatable part has a more or less aromatic, sweet, or sub-acid taste, and contains starch, grape-sugar, and malic acid. Malic acid, extracted from the apple, has long been used in medicine, and is largely employed as a mordant in dyeing.