known as chlorophyll, green, xanthophyll, yellow, and erythrophyll, red. The mingling of these three distinct colors in the plant coloring matter forms the various tints which are seen in fruits and which render them so attractive to the eye.
The sugars in fruit include both the common sugar (sucrose) and invert sugar, which contains equal quantities of dextrose and levulose. As the sugar is more or less abundant in proportion to the other ingredients the fruit is more or less sweet. The different fruits contain different quantities of sugar,—the richest perhaps is the grape which often in a state of complete maturity may have from 25 to 30 percent of sugar. Apples contain from five to 15 percent of sugar, and peaches and pears somewhat less. In fact this range in sugar will cover nearly all the fruits, large and small, as well as most of the berries. The quantity of sugar contained in each of the fruits will be especially noted in treating of them individually. One of the most important constituent of fruit from a palatable point of view is found in its organic acids. These vary in different classes of fruits. The most common organic acid in fruit is malic, which is the chief acid in the apple and allied forms. In citrus fruits, such as the lemon and orange, citric acid is the principal organic acid. In grapes the principal organic acid is tartaric. More than one of these acids is, however, usually contained in a single fruit, and other organic acids than those named are found in small quantities in various fruits. The three mentioned may be regarded as the typical acids in fruits. These acids, if prepared chemically and administered in a pure state, have practically no food value at all, and cannot be considered as wholesome material to place in the stomach. When, however, they are eaten in their natural state in combination with the potash and other bases which fruits contain, and mingled, as Nature has done, with the other constituents, they add not only to the palatability but also to the wholesomeness of the product. This is only another illustration of the fact that natural products are often wholesome and desirable where artificial products of the same kind chemically are hurtful and undesirable. Many fruits contain considerable quantities of a carbohydrate allied to some extent in its composition to sugar and starch but which has the property of setting to a semi-resilient mass known as jelly. This constituent in fruit is known as pectin or pectose and is present in greater or less quantities in almost all fruits. It is by the utilization of this component of fruit that the jellies which are so common an article of food are prepared. While in its physical properties the jelly of fruits has some resemblance to the gelatine or jelly of animals, its chemical composition and nutritive values are entirely different. The gelatine or jelly of animals is essentially a nitrogenous product while the pectin or jelly of fruit is essentially a carbohydrate product. The two, therefore, are not to be confounded.
Nutritive Uses.—The edible fruits are not only valuable on account of
