STARCH (assibilated form of stark, stiff, strong, AS. sleare, OHG. stare, Ger. stork, strong, stiff, Goth. ga-sta iirknan, to dry up; con nected with Lith. stregti, to become rigid, Pers. sat erg, strong). A form of carbohydrate (see CAmi0nynnATES), occurring as stored food in many plants. Its composition corresponds to the empirical formula but its molecular for mula, and, of course, its constitution, are as yet unknown. The number of atoms in its molecule is probably very large. Starch is formed as a condensation product from sugar by the action of certain specialized portions of the protoplasm of plant cells. The typical starch-farmers are leucoplasts (q.v.), which occur in all cells where starch is permanently stored. But the chloro plasts of the leaves may form starch when the green cells become overloaded with sugar. Thus leaves are often found to contain large quantities of starch, especially at the end of a long period of bright illumination. The sugar formed by the
process of photosynthesis (q.v.) is constantly dif fusing away into other parts of the plant, but during periods of bright light it is formed more rapidly than it can diffuse, and it is then con densed by the chloroplasts to form starch. Dur ing periods of darkness or of weak illumination, when the photosynthetic process ceases or lags, the starch of leaves is reconverted into sugar by the enzyme diastase (q.v.), and then diffuses to other regions of the plant. Thus leaves seldom contain starch in the morning or on cloudy days. But by far the greater part of the starch found in any plant is organized into grains by leuco plasts. By the action of these bodies, sugar which comes from the green leaves is condensed or polymerized into starch. Starch is thus formed in all parts of plants, being especially plentiful in tubers, in thickened roots, and in the endo sperm and embryo of seeds.