Conductors and Insulators. In a conductor, electric current can flow freely, in an insulator it cannot. Metals such as copper typify conductors, while most non-metallic solids are said to be good insulators, having extremely high resistance to the flow of charge through them.onductors and Insulators. In a conductor, electric current can flow freely, in an insulator it cannot. Metals such as copper typify conductors, while most non-metallic solids are said to be good insulators, having extremely high resistance to the flow of charge through them.
Butterhead lettuce. A type of head lettuce whose botanical name is Lactuca sativa var. heirloom. Two common types are Boston and bibb lettuce. Have small, round, loosely formed heads with soft, buttery-textured leaves ranging from pale green on the outer leaves to pale yellow-green on the inner leaves.
Iceberg lettuce and cabbage form large, round heads of light green or purple in the center of their thick, leafy foliage, of light or dark green. Broccoli and cauliflower have thick plant stems with large, compact flower heads of dark green, white, or even purple, formed at the top. Celery has light green, fibrous stems and delicate, leafy tops, but leaf lettuce, spinach, chicory, collard and Swiss chard are all leaf vegetables, although coloring varies.