Warmed-over potatoes are one of the best supper dishes. Potatoes, either freshly cooked or served a second time, are good for any meal. How shall we have potatoes for supper?

Americans are said to have the potato habit. We are told sometimes that it might be better to use oftener in their place some other starchy food, perhaps rice or hominy. These do make a pleasant change, but if you prefer potatoes, you can use them as freely as you like; and there are many ways to prepare them to give variety. In spite of the fact that potatoes are attacked by insects and by diseases which the farmer must fight steadily, they are one of our staple foods.

Why are potatoes such an important food? Recall to your minds the substances in the foodstuffs that we talked about finding in milk and in bread made from wheat. Make the list on the blackboard or on paper or in your notebook, and check them as we talk about potatoes.

Study this chart (Fig. 55) of a potato, and see if you understand it. The perpendicular lines show what a large amount of water the potato has. State 78.3 per cent in a common fraction. There is so little of the fat and protein (see the dark lines toward the left) that we do not find the worth of the potato in these. Notice the word "carbohydrate." In per cent it ranks next to the water in quantity. This is a word that you will understand when you study chemistry, but we can learn about it now that, instead of saying starch and sugar, or speaking of the starches and the sugars, the word carbo-hydrate stands for both. You remember in the lesson on bread we spoke of the fact that starch and sugar are alike, and that one can be changed into the other. The chemist has found them so much alike that he uses this name carbohydrate for both. If you wish to do so, look in the dictionary and see from what other words this one comes.

Even before you study chemistry you can learn something more about starch and sugar. Burn some sugar until it becomes entirely black. Taste this black sub-stance. You think it does not look eatable? But it is what you eat whenever you take sugar or starch; its name is "carbon," and it is the same substance that you burn in the coal in the stove. The heat has driven off the water in the sugar, and left this black carbon1 behind. We need the carbon for fuel in our bodies. We can use it when we take it in sugar and starch, although, as pure charcoal or carbon, it is useless to us as a food. Here are two questions that Miss James asked her class, and, in finding out the answers, her pupils learned one of the most wonderful of nature's true stories :

Fig. 55. - The composition of a potato.

1 United States Department of Agriculture. Office of the Experiment Stations, A. C. True, Director. Chart prepared by C. F. Langworthy, Expert in charge of Nutrition Investigations.

"Where does the plant find the carbon to make into starch and sugar?" and

"From what source came the carbon of our coal?"

Here is another way to put the question. You may have heard your father and his friends talking over the question of fertilizers. If so, they have spoken of nitrogen, phosphorus, and potash. Probably they have complained of their cost. How much does your father pay per ton for the carbon for his crops?

Energy for us in the potato. The carbon is fuel for us. It occurs in the carbohydrates, starch and sugar. Starch and a little sugar are in the potato (18 per cent); therefore, the potato gives us energy. This is one value. Ten cents' worth of potatoes at sixty cents per bushel gives us more energy than ten cents' worth of bread, even.

1 See page 299.

Mineral value of potato. Look at Fig. 55 again. In that small space at the left is pictured the other prize in the potato, the mineral matter, - the ash that cannot be burned. There is a high percentage of potassium and calcium, and of phosphorus and iron, also. These the potato takes from the soil and stores away for the young plants that would grow from the buds. Our bodies need mineral matter, too.

So let us keep on growing potatoes, in spite of Colorado beetles and the blight and scab.

The cooking class was very much amused when Mar-jorie Allen told them what her little sister said at supper the evening after they had all studied the composition of the potato. Little Alice looked at the baked potato on her plate, and said, "Which end has the mineral matter? "She thought that the chart of the potato was an exact picture. The little chart shows you how much mineral matter there would be, if it were all by itself and not mixed with the other substances in the potato.

What is a starch grain? The illustration (Fig. 56) shows you a slice of potato, magnified, before and after cooking. At the left the small bodies are the starch grains. See how the heat of the boiling temperature of water changes their shape, unfolding or bursting them. The heat also softens the fiber of the potato. Thus, with these two changes made by heat, the potato is made more digestible.

How shall we cook our potatoes? The answer to this would make a long list, and you might begin to make this list by writing down the ways that you know.

The best way to cook the potato is one that keeps in the mineral matter. If we pare the potato, we lose the mineral matter near the skin, and allow a further loss as the potato cooks in boiling water. The best ways, then, are baking, steaming, or boiling with the jackets on. Potatoes cooked in either of these three ways can be made into other "tasty" dishes. Learn how to boil a potato well; and serve it plain sometimes.

Fig. 56. - Changes of starch cells in cooking: a, cells of a raw potato with starch grains in natural condition; b, cells of a partially cooked potato; c, cells of a thoroughly boiled potato.

New and old potatoes. Potatoes are "new," fully ripe, and old. The new potato is in market in July and August, and may be known by its very thin skin. The later potatoes have a thicker skin, but the color still is fresh. In the spring after its winter storage, the potato is "old." It seems a little less firm; the color of the skin is somewhat changed; perhaps, the buds in the eyes of the potato are beginning to grow. When cooked it has a stronger flavor and a rather darker color. If the potato has been frozen, it has. a sweet taste and the quality is waxy. Potatoes are sometimes poor in quality when the season is unfavorable, or when some potato disease is prevalent.