One group of the starchy vegetables contains more protein than others. These are known as legumes. They are peas, beans, lentils. They have a power all vegetables do not share. Other plants take the nitrogen compounds they make into protein from the soil. Legumes have on their roots small tubercles or nodules in which there are bacteria that enable them to take free nitrogen directly from the atmosphere and store it in such plants for food use. Peanuts are also leguminous. Clover though not a human food is a leguminous plant, therefore has this power. By taking the free nitrogen of the air thus and making it into plant protein such plants can return the nitrogen in themselves to the soil for the plants that cannot take it from the air. This has been one method of enriching the soil. There is in many vegetables much woody fiber forming coverings and inner structure of the plant. This fiber is called cellulose. Cellulose, starch, sugar are all together termed carbohydrates in Food Science, because the elements of which they are composed are alike These differ in their quantities and arrangement, and thus make the different carbohydrates - starch, sugar, cellulose. In general carbohydrates supply heat-energy. Sugar is the carbohydrate most readily assimilated by the human system. Starch needs preparation before it can be utilized. Cellulose is only slightly digested, if at all, and then only from very young plants. There is little actual cellulose in human foods as eaten.

Tubercles on clover root.